presentation geophysical methods

An official website of the United States government

Here’s how you know

Official websites use .gov A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS A lock ( Lock A locked padlock ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

JavaScript appears to be disabled on this computer. Please click here to see any active alerts .

Geophysical Methods

Geophysics is the study of earth through the collection and analysis of physical property measurements that are recorded at or near the ground surface. Thus, geophysical methods include a vast array of techniques that apply various principles of physics to investigate the physical properties of the subsurface.

Geophysical methods can be broadly categorized by the environment in which they are applied: 

• on the earth surface,
• within a borehole/well,
• or on a surface waterbody.

Each environmentally dependent category (i.e., surface-, borehole-, and waterborne- geophysics) can be further subdivided according to the underlying physics employed within the methodology.

The list below link to general theories and applications of the method type and provide a list of commonly employed geophysical methods. Each method type includes relevant information, examples, and references.

• Surface Geophysical Methods
• Borehole Geophysical Methods
• Waterborne Geophysical Methods

The remaining portion of this site covers topics that are useful in developing a more comprehensive awareness for the use of these methods.  Such topics include:

• the geophysical properties measured with geophysical methods,
• the inversion approaches used to process and analyze the data,
• a listing of environmental geophysics terms ,
• and a list of environmental geophysics references .
• Environmental Geophysics Home
• About Environmental Geophysics
• Dielectric Permittivity
• Magnetic Susceptibility
• Electrical Conductivity and Resistivity
• Electromagnetic Properties
• Electromagnetic Signal Attenuation
• Seismic Velocities
• Seismic Reflectivity
• Geophysical References
• Publications
• Related Links

Browse Course Material

Course info.

• Prof. Robert Van Der Hilst

Departments

• Earth, Atmospheric, and Planetary Sciences

As Taught In

• Planetary Science

Learning Resource Types

Essentials of geophysics, lecture notes.

The 5 chapters presented here started off as a set of rough lecture notes and are updated every year.

Chapter 1: The Earth in the Solar System ( PDF )

1.1 Solar System Formation, Accretion, and the Early Thermal State of the Earth 1.2 Rotation and Angular Momentum 1.3 The Sun 1.4 Planetary Formation 1.5 Early Thermal State of the Earth 1.6 Radioactive Decay 1.7 Radiometric Dating 1.8 Radioactivity as a Heat Source 1.9 Meteorites and the Bulk Composition of the Earth 1.10 Chondrites 1.11 Secondary Processing 1.12 Achondrites 1.13 Irons and Stony-Irons 1.14 The Terrestrial Planets 1.15 One-dimensional Earth’s Structure 1.16 Lateral Heterogeneity in the Mantle

Chapter 2: The Earth’s Gravitational Field ( PDF - 1.0 MB )

2.1 Global Gravity, Potentials, Figure of the Earth, Geoid 2.2 Gravitational Potential due to Nearly Spherical Body 2.3 The Poisson and Laplace Equations 2.4 Cartesian and Spherical Coordinate Systems 2.5 Spherical Harmonics 2.6 Global Gravity Anomalies 2.7 Gravity Anomalies and the Reduction of Gravity Data 2.8 Correlation between Gravity Anomalies and Topography 2.9 Flexure and Gravity

Chapter 3: The Magnetic Field of the Earth ( PDF - 1.7 MB )

3.1 The Main Field 3.2 The Internal Field 3.3 The External Field 3.4 The Magnetic Induction due to a Magnetic Dipole 3.5 Magnetic Potential due to More Complex Configurations 3.6 Power Spectrum of the Magnetic Field 3.7 Downward Continuation 3.8 Secular Variation 3.9 Source of the Internal Field: The Geodynamo 3.10 Crustal Field and Rock Magnetism 3.11 Magnetization 3.12 Other Types of Magnetization 3.13 Magnetic Cleaning Procedures 3.14 Paleomagnetism 3.15 Field Reversals 3.16 Qualitative Arguments that explain the need for Core-mantle Coupling 3.17 Reversals: Time Scale, Sea Floor Spreading, Magnetic Anomalies 3.18 Magnetic Anomaly Profiles

Chapter 4: Seismology ( PDF - 1.1 MB )

4.1 Historical Perspective 4.2 Introduction 4.3 Strain 4.4 Stress 4.5 Equations of Motion, Wave Equation, P and S -waves 4.6 P and S -waves 4.7 From Vector to Scalar Potentials - Polarization 4.8 Solution by Separation of Variables 4.9 Plane Waves 4.10 Some Remarks 4.11 Nomenclature of Body Waves in Earth’s Interior 4.12 More on the Dispersion Relation 4.13 The Wave Field - Snell’s Law 4.14 Fermat’s Principle and Snell’s Law 4.15 Ray Geometries of the Wave Field 4.16 Travel Time Curves and Radial Earth Structure 4.17 Radial Earth Structure 4.18 Surface Waves 4.19 Sensitivity Kernels 4.20 Excitation of Surface Waves 4.21 Dispersion: Phase and Group Velocity 4.22 Dispersion Curves 4.23 Seismology: Free Oscillations

Chapter 5: Geodynamics ( PDF )

5.1 Heat Flow 5.2 Heat Flow, Geothermal Gradient, Diffusion 5.3 Thermal Structure of the Oceanic Lithosphere 5.4 Thermal Structure of the Oceanic Lithosphere (cont.) 5.5 Bending, or Flexure, of Thin Elastic Plate 5.6 The Upper Mantle Transition Zone

You are leaving MIT OpenCourseWare

Manual on Subsurface Investigations (2019)

Chapter: chapter 4. geophysical investigations.

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

35 C H A P T E R 4 Geophysical Investigations Introduction Geophysical investigations are used to estimate the physical properties of the subsurface by measuring, analyzing, and interpreting seismic, electrical, electromagnetic, gravitational, and magnetic fields measured at the ground surface or within boreholes. Investigations conducted from the ground surface typically provide information about the subsurface both laterally and to some depth; while most of the borehole investigations, with some exceptions, provide detailed information about subsurface materials only in the immediate vicinity of the borehole or between boreholes. In special applications, it is also possible to gather geophysical measurements of the earth over water or from airborne platforms. Geophysical methods are often useful during the initial phases of a site investigation program to efficiently gain an understanding of the overall subsurface conditions, including stratigraphy and the location and size of potential anomalies. The locations of subsequent borings and soundings can then be optimized to investigate areas of concern identified from the geophysical surveys. Geophysical methods are also useful to estimate the engineering properties of subsurface materials directly. For example, seismic methods may be used to directly measure the shear wave velocity (Vs) profile of near-surface soil and rock formations, which is required to determine the Site Class for seismic analyses (AASHTO 2011). Direct measurements of the electrical resistivity of soils via geophysical methods are useful for evaluating potential corrosion of steel pile foundations (Decker et al. 2008). Compared to more traditional forms of subsurface exploration (i.e., borings and soundings), geophysical methods offer several advantages (Wightman et al. 2003, Anderson et al. 2008, AASHTO 2017): • Because surface geophysical methods are noninvasive, they provide the ability to cover a large area in a time- and cost-effective manner to gain an understanding of the overall subsurface conditions. As noted above, this enables optimizing the locations of borings and soundings during subsequent phases of a subsurface exploration program or interpolating between existing borings and soundings. This is particularly true for linear projects (e.g., highway construction). • Geophysical methods are robust in the sense that they are based on fundamental physical principles with relatively little reliance on empiricism. In many cases, the methods used for geotechnical applications leverage the extensive experience gained with similar methods developed for resource (e.g., oil, gas) exploration. • Surface geophysical methods are also useful for sites where borings and soundings are difficult or impractical, such as gravel deposits or contaminated soils. The equipment used for many geophysical tests is highly portable, which may allow testing at sites that are not easily accessible (e.g., a heavily wooded area) using conventional drilling equipment. It is also important to recognize the limitations of geophysical methods to avoid using them in situations where there may be a low probability of success: • Geophysical methods are more likely to yield good results when (i) there is a large contrast in seismic, electrical, electromagnetic, gravitational, or magnetic properties between lithologic units or between an anomaly and the surrounding soils and rocks, and (ii) the subsurface features of interest are of sufficient size relative to their depth that they are within the limits of detection for a particular geophysical method.

36 • The interpreted subsurface conditions may not be unique for many geophysical methods; there may be multiple, physically plausible interpretations for the stratigraphy or location and size of anomalies that all yield the same measured geophysical response. For example, a structural low in bedrock topography; a small, air-filled void in the bedrock; or a larger, water-filled void in the bedrock may all produce the same magnitude of gravity anomaly. • Sites that have a stiff, surficial layer overlying a weaker layer or an electrically resistive layer over a conductive layer pose a challenge for many surface geophysical tests. For example, many seismic methods do not work well on concrete pavements because of the large stiffness of the pavement compared to the base and subgrade materials. In part because of these limitations and in part because geophysical methods are less familiar to many geotechnical engineers than conventional site investigation methods (e.g., SPT, CPT), it is essential that geophysical investigations be conducted by personnel who are trained and experienced in near-surface geophysics. Finally, in all but a few applications (e.g., reconnaissance-only investigations), the results of geophysical investigations should always be complemented by direct observation of subsurface conditions by means of borings, soundings, test pits, trenches, outcrops, and other geological information. This ground truth information will help ensure that interpreted subsurface conditions derived from geophysical methods are as accurate as possible. The combined use of a geophysical investigation with direct observation is a robust approach to developing an accurate ground model for a project. Planning a Geophysical Investigation There are a number of surface and borehole geophysical methods available to choose from when planning a geophysical site investigation. Selecting one or more methods for a project can be guided by answering the following questions (Anderson et al. 2008): • What are the physical properties of interest? • Which methods respond to the physical properties of interest? • Which methods can provide the required levels of detection and resolution for the subsurface features of interest? • Which methods can perform well given conditions at the project site? • Which methods provide complementary information to help improve interpretations based on the observed data? • What direct observations (e.g., borings or soundings) should be performed to constrain the interpretation of geophysical data? • Which methods are most cost effective, and is the overall geophysical investigation cost effective? Anderson et al. (2008) provide additional discussion and examples for each of these considerations. Surface Geophysical Methods This section summarizes surface geophysical methods—seismic, electrical, electromagnetic, and potential-field methods—that can be used for a variety of subsurface-investigation objectives for transportation-related projects as shown in Table 4-1. Further guidance is provided in ASTM D6429. For many applications, more than one method may be capable of achieving the objective. In these cases, an experienced geophysicist can evaluate what methods have the highest likelihood of success for a particular project based on site-specific conditions.

37 Table 4-1. Matrix of surface geophysical methods in relation to investigation objectives Objective Seismic Electrical and Electromagnetic Potential Field R ef ra ct io n an d R ef le ct io n Su rf ac e W av e R es is tiv ity El ec tr om ag ne tic G ro un d- Pe ne tr at in g R ad ar M ic ro gr av ity M ag ne to m et ry Se lf- Po te nt ia l Lithology and stratigraphy      Bedrock topography        Water table    Rippability  Shear wave velocity profile  Fault detection      Void and cavity detection       Subsurface fluid flow   Ferrous anomalies    Conductive anomalies     Corrosion potential  Sources: Fenning and Hasan (1995), USACE (1995), Sirles (2006), FHWA (2006), Anderson et al. (2008) There are many readily available references that describe these geophysical methods in detail (e.g., USACE 1995, Wightman et al. 2003, Sirles 2006, Anderson et al. 2008), and additional information is available in the ASTM guides and standards listed in Table 4-2. The focus in this section is to briefly summarize the key features of the surface geophysical methods that are used for transportation applications and provide examples of the results obtained for each. Table 4-2. ASTM guides and standards for surface geophysical investigations Geophysical Method ASTM Guide or Standard Standard Guide for Selecting Surface Geophysical Methods D6429 Seismic Refraction D5777 Seismic Reflection D7128 Electrical Resistivity D6431 Soil Resistivity G57 Frequency-domain electromagnetics D6639

38 Geophysical Method ASTM Guide or Standard Time-domain electromagnetic D6820 Ground-penetrating radar D6432 Microgravity D6430 Source: Sirles (2006) 4.3.1 Seismic Methods Seismic methods use measurements of the velocity of mechanical (i.e., stress) waves propagating through the ground to infer stratigraphy from contrasts in seismic velocity between layers and to evaluate the small- strain stiffness (i.e., modulus) of subsurface materials. Depending on the specific method, either body (i.e., compression and shear) waves or surface (i.e., Rayleigh) waves are used. Typical ranges of the compression (or P) wave velocity (Vp) and shear (or S) wave velocity (Vs) for earth materials are shown in Figure 4-1. 0 5,000 10,000 15,000 20,000 25,000 Compression Wave Velocity, Vp (ft/s) Water Clay Sand Till Weathered Rocks Intact Rocks Steel

39 Source: Bourbie et al. (1987), USACE (1995), Mavko et al. (1998), Santamarina et al. (2001), FHWA (2002) Figure 4-1. Typical ranges of compression (top) and shear wave velocity (bottom) The compression wave velocity is directly related to the constrained modulus of the material: = where M = the initial tangent constrained modulus = the total mass density of the material Similarly, the shear wave velocity is directly related to the shear modulus: = where G = the initial tangent shear modulus The compression wave velocity is greater than the shear wave velocity, with the ratio depending on the Poisson’s ratio of the material. Because the strain levels associated with the propagation of seismic waves through the ground are very small for most seismic methods, the constrained and shear moduli correspond to the initial tangent (i.e., maximum) stiffness. These simple, fundamental equations are the basis of one of the most attractive features of seismic methods⎯in situ measurements of compression and shear wave velocity may be used to directly measure the small-strain moduli of soil and rock, which are useful for evaluating deformations related to serviceability limit states. In saturated soils, the measured compression wave velocity often reflects the properties of the pore fluid in the voids (Allen et al. 1980). As such, measurements of compression wave velocity in saturated soils are 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 Shear Wave Velocity, Vs (ft/s) Clay Sand Till Weathered Rocks Intact Rocks Steel

40 often of limited value for determining the properties of the soil itself. In these cases, the shear wave velocity is a more useful quantity because it is mostly unaffected by the presence of fluid in the voids. 4.3.1.1 Seismic Refraction and Reflection When compression and shear waves encounter an interface between two dissimilar materials, some of the energy is reflected by the interface and some is transmitted (i.e., refracted). The characteristics of the reflected and transmitted waves are governed by the physics of wave propagation in layered media (e.g., Ewing et al. 1957). The seismic refraction test is based on measuring the travel time of critically refracted (i.e., angle of refraction = 90°) compression or shear waves along the interfaces between different lithologic formations. Seismic refraction data is collected using a linear array (spread) of vertical geophones to record first arrivals of compression waves generated from a weight drop or explosive source. Although seismic refraction tests can also be conducted using shear waves, it is less common. The geophones are connected via a geophone cable to an engineering seismograph. The production rate can be increased significantly by using a towed land streamer rather than placing the geophones individually. The land streamer consists of geophones attached to a sled or high-strength sleeve, and it allows the entire array to be moved simultaneously while maintaining a fixed spacing. Energy sources range from sledgehammers for shorter arrays and shallow depths to explosive sources for longer arrays and deeper depths. For each geophone spread, multiple source locations (shot points) at the ends and in the center of the spread are used; more shot points should be used if large lateral variations in subsurface stratigraphy are expected. Seismic refraction processing steps include filtering to reduce the effect of unwanted noise, selecting the first-arrival time for each geophone and shot point, and plotting the travel times vs. geophone offset. Several methods are available to interpret the data, including the simple intercept-time method, Generalized Reciprocal Method, and seismic refraction tomography. The Generalized Reciprocal Method (Palmer 1981) is widely used because it provides the depth and seismic velocities of refractors below each geophone location and can accommodate nonplanar refractors (i.e., layer interfaces) and lateral variations in seismic velocity within a single geophone spread. The most important limitation of these interpretation methods is the hidden layer problem that occurs when either (i) a low-velocity layer underlies a high-velocity layer (i.e., velocity reversals) or (ii) there are thin layers with insufficient velocity contrasts. Seismic refraction tomography (White 1989, Zhang and Toksoz 1998) is a more advanced interpretation method capable of calculating a two-dimensional (2D) velocity structure by minimizing the difference between predicted and observed first-arrival travel times. It is supplanting the intercept-time method and Generalized Reciprocal Method for geotechnical applications because the aforementioned hidden-layer problem is minimized. The most common application of the seismic refraction test is to evaluate the stratigraphy of various lithologic units, particularly the interface between soil and rock because of the contrast in seismic velocity between these two materials. An example is shown in Figure 4-2 of using the measured vertical and lateral variation of compression wave velocity to estimate the depth to bedrock. The black plus signs indicate the depth to bedrock observed in soil borings.

41 Source: Geosyntec Consultants, Inc. Figure 4-2. Example seismic refraction tomography test results Seismic refraction is also used to estimate the rippability of bedrock (Caterpillar Inc. 2000) based on the compression wave velocity using relationships like that shown in Figure 4-3. Source: Caterpillar, Inc. Figure 4-3. Estimated D8R ripper performance from seismic velocity The seismic reflection method is based on measuring the travel time of seismic waves that are reflected by the interface between different lithologic units. Geotechnical applications of seismic reflection (often called shallow or high-resolution seismic reflection) have benefited from the experience gained from the extensive use of the method for resource exploration. Seismic reflection data are also collected using a linear array of geophones, a seismograph with a corresponding number of channels, and an appropriate energy source. Like the seismic refraction test, land streamers are commonly used to expedite testing. Energy sources used include blank shotgun shells fired using a Buffalo gun, explosives, and swept- frequency sources (e.g., Vibroseis). The processing of shallow seismic reflection data is often complex and requires considerable skill and experience. Processing steps may include the following: • Filtering and scaling each record • Muting to remove ground roll (i.e., surface waves) • Making static corrections for elevation changes and variable thickness of near-surface zones

42 • Correcting for normal move-out • Migrating to correct for dip of subsurface reflectors Subsequent data interpretation can be subjective. Other data, such as boring logs, may be used to generate synthetic seismograms to correlate with measured seismic reflection data to check the reasonableness of interpreted sections. The shallow seismic reflection method (Steeples and Miller 1990) is less common for geotechnical site characterization than other seismic methods, in part due to cost and the extensive data processing requirements. However, many near-surface geophysical practitioners have been successful in using shallow seismic reflection to map depth to bedrock, locate faults, image abandoned mines, and identify areas prone to subsidence from sinkholes (e.g., Hunter et al. 1984, Steeples and Miller 1990, Miller and Steeples 2008, Pugin et al. 2009). An example of mapping the interface between soil and bedrock is shown in Figure 4-4. Figure 4-4(a) shows the processed depth section, while Figure 4-4(b) is the interpreted section identifying the bedrock surface. Note the borehole located at about 4,500 meters that correlates well with the seismic reflection section. A second example is shown in Figure 4-5 of a seismic reflection section along an interstate highway that was used to identify the location and lateral extent of sinkholes. The sinkholes are located at approximately stations 1340 and 1500. Source: Pugin et al. (2009) Figure 4-4. Seismic reflection section showing depth to bedrock

43 Source: Miller and Steeples (2008) Figure 4-5. Seismic reflection section showing sinkhole locations 4.3.1.2 Surface Wave Methods Surface wave methods use the dispersive nature of Rayleigh (i.e., surface) wave propagation in a vertically layered medium to develop 1D shear wave velocity profiles. Surface-wave tests may be conducted using an active source, such as a sledge hammer or dropped weight; it is also possible to use large, swept-frequency vibrators (e.g., Vibroseis) to generate low-frequency Rayleigh waves that enable deeper profiling. A linear array of vertical, low-frequency geophones is used to record data. Like seismic refraction and reflection, a land streamer can be used to expedite testing. Surface wave seismic data can be collected using passive sources of Rayleigh waves such as ambient noise. Passive sources generally produce energy at lower frequencies (e.g., 2 to 10 Hertz [Hz]) than most active sources and thus allow deeper profiling. However, passive tests may be impractical at some sites, especially those located in rural areas, because of insufficient ambient noise. For passive-source measurements, a 2D array of geophones is commonly used because the location of the source(s) of passive energy is usually unknown. An alternative approach, called the refraction microtremor (ReMi) technique (Louie 2001), uses a linear array of geophones. The passive ReMi technique assumes an omnidirectional wavefield that should be verified for each test (Foti et al. 2015). However, the ReMi method can also accommodate active collinear sources, similar to other active-source surface-wave methods. At many sites, it is advantageous to combine active and passive tests to obtain data over a broad range of frequencies.

44 The processing steps consist of (i) calculating an experimental dispersion curve that shows the variation of Rayleigh wave phase velocity with frequency (or wavelength) and (ii) performing an inversion of the experimental dispersion curve to obtain the profile. An example dispersion curve is presented in Figure 4-6. There are many variants of surface wave methods that have been developed, including the Spectral Analysis of Surface Waves (SASW) and Multichannel Analysis of Surface Waves (MASW) methods, among others. Typically, the differences between these variants include the type of source (active or passive), the shape of the receiver array (2d or linear), and the specific techniques used to calculate the experimental dispersion curve and perform the inversion to obtain the profile. Source: Geosyntec Consultants, Inc. Figure 4-6. Example Rayleigh-wave dispersion curve The inversion process results in a 1D profile. As noted previously, the profile is useful for seismic site response analyses (AASHTO 2011). Multiple 1D models generated from a series of array locations can be combined and presented as a 2D cross section of shear wave velocity. Because shear wave velocity is directly related to the stiffness of subsurface materials, 2D models are valuable in estimating the depth to rock and delineating loose zones in the subsurface. Figure 4-7 shows an example of using an MASW test to identify the top of a firm sand layer. Additional guidance on performing surface wave tests is available in Foti et al. (2015, 2018). Source: Geosyntec Consultants, Inc. Figure 4-7. Example 2D shear wave velocity cross section from MASW test

45 4.3.2 Electrical and Electromagnetic Methods Electrical and electromagnetic geophysical methods use the flow of electrical currents through the ground to evaluate subsurface characteristics. Electrical (or galvanic) methods commonly induce the currents via electrodes that are directly coupled to the ground and measure the resulting potential (i.e., voltage) difference via a separate pair of electrodes. But it is also possible to measure currents and potentials that occur naturally due to subsurface processes. Electromagnetic (or induction) methods use eddy currents that are induced in the ground by time-varying magnetic fields generated by an electrical current within coils that are not directly coupled to the ground. From these measurements, the vertical and lateral distribution of electrical resistivity (or its inverse– conductivity) can be calculated. Because the resistivity of earth materials is affected by mineralogy, porosity, chemistry of the pore fluids, and degree of saturation, electrical resistivity surveys can be used to define subsurface layering, locate cavities, and delineate the groundwater table. For example, clays tend to have low resistivities because of the presence of exchangeable cations in the pore fluids, while sands containing fresh water have higher resistivities. The resistivity of an earth material usually decreases as the moisture content of the material increases. The resistivity of selected earth materials is given in Figure 4-8. Source: ICE (1976), USACE (1995) Figure 4-8. Typical ranges of electrical resistivity 4.3.2.1 Resistivity Traditionally, an electrical resistivity array consists of four electrodes that are coupled to the ground. Two of the electrodes transmit an electrical current ( ) to the ground and the other two electrodes measure the change in potential ( ) in the earth materials between the current electrodes. The apparent resistivity ( ) is a function of the measured electrical impedance ( = ⁄ ): = where = the geometric factor that depends on the configuration and spacing of the electrodes Three configurations of four-electrode arrays have been commonly used in electrical resistivity surveys: (i) the Schlumberger array, (ii) the Wenner array, and (iii) the dipole-dipole array. These array configurations differ in their vertical and horizontal resolution; signal-to-noise ratio; susceptibility to 1 10 100 1,000 10,000 100,000 1,000,000 Resistivity, ρ (ohm-meters) Igneous rocks Metamorphic rocks Dense Limestone Porous Limestone Shale Sand, wet to moist Clay

46 electromagnetic coupling; and ease of field implementation, automated data acquisition, and interpretation. Additional array configurations are available for specific objectives (Zonge et al. 2005). The Wenner and dipole-dipole arrays readily adapt to modern automatic data acquisition systems employing multielectrode cables. The measured apparent resistivities are average resistivities of all the earth materials through which the electrical current flows. As the electrode spacing is increased, the electrical current flows through more material, and the apparent resistivities calculated from the field arrays represent averages over a larger volume. The measured apparent resistivities can be interpreted to evaluate subsurface features using several approaches of increasing complexity: • Pseudosections (profile plots of 2D apparent resistivity) are generated from the resistivity measurements. For relatively simple, nearly homogeneous profiles, the pseudosection gives a reasonable approximation of the vertical and lateral distribution of actual resistivities. Because computers have made more complex, accurate methods of interpretation possible, pseudosections are now primarily used for quality control during field acquisition. • Closed-form expressions are available that relate the apparent resistivity to the resistivity and thickness of individuals layers in a 1D, multilayer earth model. Algorithms have been developed that automatically adjust the resistivity and thickness of individuals layers until satisfactory agreement is obtained between the calculated and measured apparent resistivity values as a function of electrode spacing. • Electrical resistivity tomography or electrical resistivity imaging are based on using numerous combinations of four-electrode arrays from a large, multielectrode cable. For each four-electrode array, the calculated and measured pseudosections are compared, and the resistivities within a 2D or 3D model are adjusted until satisfactory agreement is obtained. The numerous combinations of arrays provide ample data to develop detailed models. An example of electrical resistivity imaging test results is shown in Figure 4-9. The low-resistivity materials are interpreted to be caused by (i) higher porosity due to weathering of carbonate bedrock and (ii) higher water content. Source: Geosyntec Consultants, Inc. Figure 4-9. Example electrical resistivity imaging results Induced polarization methods are closely related to resistivity methods, but they include an additional measurement called chargeability, which is a measure of the energy storage capacity of a material. The additional parameter aids with identifying anomalies and has proven effective for mapping landfills and contaminant plumes (Zonge et al. 2005).

47 4.3.2.2 Electromagnetic Methods Electromagnetic methods can be broadly divided into two groups: Frequency-domain electromagnetics (FDEM) methods and time-domain electromagnetic (TDEM) methods. In FDEM methods, a transmitter coil emits a sinusoidally varying current at a specific frequency. A receiver coil measures the secondary field generated by the induced eddy currents in the subsurface. The amplitude of the secondary field is usually expressed as a percentage of the primary field at the receiver. The phase shift caused by the time delay in the received field can also be measured. An alternative is to separate the received field into two components. The first component is in phase with the transmitted field, and the second component is 90° out-of-phase with the transmitted field. The in-phase component is sometimes called the real component, and the out-of-phase component is sometimes called the quadrature or imaginary component. The most common type of FDEM method for engineering applications is the terrain conductivity method (McNeill 1990). Terrain conductivity electromagnetic systems are instruments that use two loops or coils as transmitter and receiver, respectively. For shallow profiling, the two coils are located a fixed distance apart in a boom that is carried by one person. For deeper profiling, two people are needed: one person generally carries the transmitter coil, while a second person carries the second coil that receives the primary and secondary fields. Terrain conductivity meters are operated in both the horizontal and vertical dipole modes. These terms describe the orientation of the transmitter and receiver coils to each other and the ground, and each mode gives a significantly different response with depth. When used in the vertical dipole mode, the instruments are more sensitive to the presence of relatively conductive, steeply dipping structures; whereas in the horizontal dipole mode, the instruments are relatively insensitive to this type of structure and can give accurate measurement of ground conductivity near them. Because terrain conductivity meters read directly in apparent conductivity and most surveys using the instrument are done in the profile mode, interpretation is usually qualitative and used to identify anomalies. Any anomalous areas are investigated further with other geophysical techniques or borings and soundings. Information about the variation of conductivity with depth can be obtained by measuring two or more coil orientations or intercoil separations, or both, and using commercially available software to perform an inversion of the measured data to obtain a 1D profile of conductivity at the sounding location. Figure 4-10 shows the results of a terrain conductivity survey performed to identify areas of high conductivity corresponding to buried waste and contaminated soils prior to site development.

48 Source: Spotlight Geophysical Services, LLC Figure 4-10. Example terrain conductivity results A common TDEM resistivity sounding survey consists of a square transmitter coil laid on the ground and a receiver coil located in the center of the transmitter coil. The TDEM method measures the decaying secondary field induced in the subsurface by the current in the transmitter coil. By making measurement of the voltage out of the receiver coil at successively later times, measurement is made of the current flow and, thus, also of the electrical resistivity of the earth at successively greater depths. The measured apparent resistivity as a function of time can be interpreted using commercially available software to calculate a 1D profile of resistivity at the sounding location. 4.3.2.3. Ground-Penetrating Radar Ground-penetrating radar (GPR) uses an electromagnetic pulse transmitted from a radar antenna to probe the subsurface. The transmitted, high-frequency electromagnetic pulses are reflected from various interfaces within the ground, and the reflected pulse is detected by a receiver antenna. Reflecting interfaces may be soil horizons, the groundwater surface, soil-rock interfaces, man-made objects, or any other interface possessing a contrast in dielectric properties. GPR has found widespread use for transportation applications (Sirles 2006), and the following are common applications (Morey 1998): • Measuring pavement thickness • Locating voids beneath pavements • Evaluating delamination in bridge decks • Estimating depth to bedrock and the groundwater table

49 • Mapping underground utilities and other buried objects such as tanks and drums GPR antennas are designated by their center frequency and range from approximately 10 megahertz (MHz) for mapping deep subsurface stratigraphy to approximately 3,000 MHz for shallow rebar mapping. The antennas may be placed on the ground surface (i.e., ground-coupled) or suspended above the ground surface (i.e., air-launched). The latter is often mounted on a vehicle and used for pavement studies to allow surveys to be conducted at highway speeds. A typical mode of operation is the common-offset mode where the transmitter and receiver antennas are maintained at a fixed separation distance and moved along a survey line. Measurements are taken at specific distance or time intervals as needed. The reflected pulses are recorded as a function of time and may be converted to an approximate depth using an estimated velocity or the reflection time of a known feature such as a drain pipe. As the antennas are moved along the survey line, the output is displayed as a cross section or radar image of the subsurface. Resolution of interfaces and discrete objects is typically very good due to the short wavelengths associated with the electromagnetic pulses. However, the attenuation of the pulses in earth materials may be high, and depth penetration may be limited. This is particularly true in highly conductive soils such as clays where penetration may be limited to a few feet. In low-conductivity sands, the penetration depths are potentially much greater, up to approximately 150 ft (45 m). The majority of GPR applications use 2D sections that have been corrected for attenuation by applying a gain function. Further data processing, when needed, is similar to that used for seismic reflection data. Available processing steps include frequency filtering to remove noise, spatial filtering to remove horizontal noise, and migration to collapse diffractions and move dipping reflectors to their actual position. While 2D profiles are sufficient for most projects, 3D processing of GPR data collected along closely spaced lines can provide more accurate and quicker evaluation of specific targets, such as voids, and better visualization of subsurface features. Figures 4-11 and 4-12 present examples showing the use of a GPR test to identify the base of a fill layer and a void under a continuously reinforced concrete pavement. Source: Spotlight Geophysical Services, LLC Figure 4-11. Example GPR results showing base of fill layer

50 Source: Texas DOT Notes: CRCP: continuously reinforced concrete pavement Figure 4-12. Example GPR results showing pavement void detection 4.3.3 Potential Field Methods Examples of potential fields include gravitational, magnetic, and electrical fields. Several geophysical methods are based on measuring local changes in these potential fields for identifying subsurface features. 4.3.3.1 Microgravity Gravity methods involve measuring anomalies in the gravitational field of the Earth due to differences in the densities of materials in the subsurface. For example, an air-filled solution cavity has a different density than surrounding rock units, which would result in a gravity anomaly, or a low in the bedrock surface would appear as an anomaly when compared to the gravity readings in surrounding terrain. A gravity study to evaluate near-surface voids and loose zones is often referred to as a microgravity survey, indicating the magnitude of the gravity anomalies that are measured, typically in the microgal (µgal) range (1 µgal ≈ 10-9 g). Typical applications of microgravity surveys in transportation include mapping bedrock topography and identifying voids and loose zones caused by karst activity or underground mining. The resolution of a gravity survey depends on the sensitivity of the gravimeter and on the density contrast between different units in the subsurface. Microgravity surveys are conducted by taking measurements at specific stations along a line or at grid points. The stations should be spaced close enough each other to adequately define the subsurface conditions of interest. The elevation of each station must be obtained accurately, typically within ±1 in. (±2 cm) for a data accuracy on the order of a few µgals. The horizontal station accuracy is not as critical as elevation, and differential global positioning system (GPS) values are usually sufficient. The measurements are made by placing the gravity meter on the ground surface, leveling the meter (or use a self-leveling meter), and waiting for the reading to stabilize before recording the reading. At least once per hour, the gravity meter should be returned to a reference location (i.e., base station) to monitor temporal changes in the local gravitational field and check for instrument drift.

51 The processing steps for microgravity surveys include making corrections to the measured data for (i) instrument drift (using base station readings), (ii) Earth tides (using published models), (iii) latitude (using measured horizontal location), and (iv) elevation differences compared to a reference datum. The last process step in the list, comparing the elevation differences to a reference datum, is done in two steps: 1. A free-air correction to compensate for the change in gravity due to the elevation of a station above the reference datum 2. A Bouguer correction to compensate for the mass of soil or rock between the gravity station and the datum. The corrected value is the simple Bouguer anomaly and is the value typically used for data interpretation. Terrain corrections may also be required if the surrounding terrain is not relatively flat (Long and Kaufmann 2013). Processed microgravity data can be presented as a profile line (Figure 4-13) or, in the case of a grid study, as a contour map (Figure 4-14). Gravity anomaly sources can be modeled, if needed, but anomalies are often just used as a guide to select locations for drilling or excavation. Source: Spotlight Geophysical Services, LLC Figure 4-13. Example of a microgravity profile

52 Source: Spotlight Geophysical Services, LLC Figure 4-14. Example of a microgravity contour map 4.3.3.2 Magnetometry Magnetic surveys measure changes in the magnitude in the magnetic field of the Earth due to the presence of ferrous metal objects or by Earth materials that have high magnetic susceptibilities. Common targets for a magnetic survey include buried (ferrous) metal objects such as tanks, pipelines, and steel-cased wells; although the use of magnetometers has been replaced in some applications by electromagnetic induction metal detectors due to the higher lateral resolution of the metal detectors. Magnetic surveys can also be used to map the bedrock surface if the rock is known to have a high magnetic susceptibility. Examples of the latter include rocks that have unusually high magnetic susceptibilities (e.g., gabbro, basalt) as well as other types of rock that contain significant amounts of ferrous minerals (e.g., manganese, magnetite, hematite). Prior to conducting a magnetometer study, solar storm activity should be checked, as this may affect the Earth’s magnetic field. The National Oceanic and Atmospheric Administration (NOAA) Space Weather Prediction Center maintains a website that tracks and predicts solar activity. Magnetometer data can be collected at specific fixed stations but usually is recorded while the operator is walking along a survey line or grid using GPS for positioning. Data stations should not be located near any man-made object that can change the magnitude of the Earth's magnetic field (e.g., power transmission lines, automobiles, metal pipelines and fences, structural steel in roads and buildings). The operator should also avoid having metallic objects on their person (e.g., steel-toe boots, metal belt buckles). The total magnetic field is measured in units of nanoTesla (nT) by a single-sensor magnetometer and using a base station to record diurnal changes in the Earth’s magnetic field. The need for a base station can be eliminated by using a two-sensor gradiometer that measures the vertical or horizontal gradient of the field. The vertical gradient cancels out diurnal changes and resolves shallow metallic objects better than single-sensor magnetometer data because it measures the rate of change between the readings of the two sensors (the gradient) rather than the total field. Data processing steps will depend on the type of instrument used (i.e., single-sensor magnetometer or gradiometer). For both types, the data is initially filtered to remove high-frequency noise. For a single- sensor magnetometer, subtracting the base station readings from the readings at other stations removes the

53 time-varying changes in the magnetic field (and the value of the field at the base station location). Long- wavelength filtering (e.g., subtracting a best-fit polynomial) can be used to remove regional changes in the field over the area of the survey, producing a total field anomaly map. Due to the inclination and declination of the Earth’s magnetic field, magnetometer anomalies over a single magnetic object will appear dipolar, and the peak response will be offset laterally from the source of the anomaly. The reduction-to-pole processing available in commercial software corrects for inclination and declination and converts the dipole anomaly to a monopole anomaly that is centered over the anomaly. The use of a gradiometer eliminates much of the processing required for single-sensor data. However, the vertical gradient of the field, while highlighting the response from shallow ferrous objects, emphasizes the slope of the magnetic field so that the peak response is offset from the source of the anomaly. The results of a magnetometer survey can be presented as a profile line or as a contour map. The presented data should include the location of known metallic objects so that anomalies from these objects will not be mistaken as targets of interest. 4.3.3.3 Self-Potential The self-potential (SP) method, also called the spontaneous potential method, measures the naturally occurring voltage differences caused by water moving through a porous medium. A common geotechnical application for the SP method is to map seepage paths from dams and reservoirs (e.g., Jansen et al. 1994). Other applications include mapping groundwater flow around pumping wells or around faults. SP measurements are made using nonpolarizable (porous pot) electrodes that have a porous ceramic tip, contain a copper rod, and are filled with a conductive solution of copper-sulfate. A reference electrode is placed in a fixed location, while a rover electrode is moved from location to location. The two electrodes are connected to a high-impedance multimeter to measure the voltage difference between the two locations. Measurements are typically made by inserting the rover electrode in shallow hand-auger holes, 6 to 12 in. (15 to 30 cm) deep to contact moist soils. SP data are usually collected along parallel lines with measurements made at a fixed spacing such as 5 or 10 ft (1.5 to 3 m). In addition to variations caused by water seepage, measurements are affected by corroding metal, electrode polarization and drift, changes in moisture in the soil at the base station, and variation in natural telluric currents (Corwin 1990). Corrections must be made for these sources of noise. SP data can be plotted as a single curve or, if collected using a grid of lines, as a contour map. Typically, SP data are evaluated qualitatively, although quantitative methods exist (Corwin 1990). Borehole Geophysical Methods There are two general categories of borehole geophysical tests used for geotechnical subsurface explorations: (i) borehole-to-borehole and surface-to-borehole methods, and (ii) in-hole logging methods. The in-hole logging methods are often based on methods developed for resource exploration and adapted for near-surface applications. This section provides a summary of borehole geophysical methods that have applications for transportation-related projects as shown in Table 4-3. Further guidance is provided in the ASTM guides for borehole geophysical methods listed in Table 4-4.

54 Table 4-3. Matrix of borehole geophysical methods in relation to investigation objectives Objectives Se is m ic C ro ss ho le Se is m ic D ow nh ol e C al ip er R es is tiv ity Sp on ta ne ou s Po te nt ia l In du ct io n N at ur al G am m a G am m a- G am m a D en si ty N eu tr on P or os ity A co us tic T el ev ie w er Se is m ic L og gi ng 1 Lithology       Seismic wave velocity profile    Fracture location and characteristics   Density, porosity, and water content   Borehole diameter  Source: Paillet and Ellefsen (2005) Table 4-4. ASTM guides for borehole geophysical investigations Geophysical Method ASTM Guide Standard Guide for Conducting Borehole Geophysical Logging D5753 Mechanical Caliper D6167 Natural Gamma and Gamma-Gamma Density D6274 Electromagnetic Induction D6726 Neutron D6727 Crosshole Seismic Testing D4428 Downhole Seismic Testing D7400 Source: Sirles (2006) 4.4.1 Borehole-to-Borehole and Surface-to-Borehole Methods The seismic crosshole and downhole methods have been used in geotechnical engineering for many years to measure compression ( ) and shear wave velocity ( ) profiles, with the latter being of valuable for determining the site class (AASHTO 2011) or analyzing seismic site response. As noted previously, seismic velocities may also be used to calculate small-strain moduli in soil and rock.

55 4.4.1.1 Seismic Crosshole Method The seismic crosshole method is conceptually simple. Compression and shear waves are generated in one borehole, and the arrival of those waves is recorded in one or more additional boreholes by a geophone at the same depth. By moving the source and geophones(s) up and down the boreholes in unison, a profile of compression and shear wave velocity vs. depth can be generated. The boreholes are commonly 10 to 15 ft (3 to 4.5 m) apart and are typically cased to prevent collapse. Cement grout ensures good physical coupling between the casing and surrounding soil to enable seismic waves to be recorded accurately. Sources for compression wave surveys include electrical discharge sources and air guns for water-filled boreholes, and downhole hammers for both water-filled and dry boreholes. A source that clamps to the inside of the casing and generates a vertical shearing motion can be used for shear wave velocity surveys. One or more geophones are placed in the adjacent boreholes at the same depth as the source. Generally, measurements are repeated at 2-ft (0.6-m) depth intervals from the ground surface to 20 ft (6 m). Below 20 ft (6 m), measurements are usually taken at 5-ft (1.5-m) depth intervals to the maximum depth of the boreholes. Because the seismic wave velocities calculated from the observed travel times depend directly on the distance of travel between boreholes, it is critical to accurately measure this distance as a function of depth. The location of the top of each boring (i.e., top of casing) can be located by land surveying techniques; the borehole deviation can be measured using an inclinometer. The travel time of the seismic waves may be determined by identifying the initial arrival of compression and shear waves. Examples of recorded waveforms are shown in Figure 4-15, along with the selection of the arrival times of shear waves and the calculated travel time (Δt). Alternatively, the travel time can be determined via cross correlation; peaks in the cross-correlation function correspond to the time lag (i.e., travel time) between two or more geophones. The velocity is then determined using the calculated distance between boreholes at the corresponding depth. Although it is assumed that the measured wave velocity is for a seismic wave traveling directly between boreholes, it is important to consider that refraction through a higher-velocity layer above or below the source-receiver depth may produce the first arrival. One way to minimize the potential for refraction is to limit the distance between boreholes. Source: Geosyntec Consultants, Inc. Figure 4-15. Example seismic crosshole data

56 4.4.1.2 Seismic Downhole Method For seismic downhole measurements, a source on the ground surface is used to generate compression and shear waves, and arrivals are recorded by one or more geophones placed in a borehole. For tests conducted in soils, the borehole is usually cased to avoid collapse. Care must be taken in grouting the casing to prevent voids in the borehole annulus that can prevent the seismic waves from reaching the geophones. The source is located approximately 5 to 15 ft (1.5 to 4.5 m) from the borehole to reduce the potential for generating seismic waves in the casing itself. For shear wave measurements, a beam or plank in contact with the ground surface is struck to generate horizontally polarized shear waves. Automatic shear wave sources, such as the autoseis described in Chapter 5, may also be used. For compression wave measurements, a sledgehammer striking a metal plate on the ground surface is sufficient. The geophone is lowered down the borehole at 2-ft to 5-ft (0.6-m to 1.5-m) intervals. At each depth interval, the arrival of compression and shear waves is recorded. A limitation of the method is that the amplitude of the wave arrivals diminished with depth due to attenuation. If necessary, the records from multiple source activations can be added together (i.e., stacked) to increase the signal-to-noise ratio. Arrival times for the compression and shear waves are selected and used to calculate the corresponding wave velocity profile. If two or more geophones are used, the wave velocity may be calculated using a true- interval method where the travel time between the geophones is calculated for a single activation of the source. This is desirable because the two seismic waveforms should have similar shapes, making it easier to identify the arrivals and avoid the need for a source trigger. If only one geophone is available, a pseudo- interval travel time must be calculated as the difference between the source-to-receiver travel times when the single geophone is at two different depths. If the travel time is calculated over a small depth interval, the velocities are sensitive to errors in choosing arrival times. This may be overcome by using travel-time measurements at several adjacent depths to calculate an average velocity. The most common variant of the seismic downhole method in use is the seismic piezocone test described in Chapter 5. See Section 5.3.1.3 for further details. Figure 4-16 shows an example from a seismic piezocone test where seismic tests were performed at 3.3-ft (1-m) depth intervals to a total depth of approximately 260 ft (80 m). The red symbols indicate the first crossover point on each waveform, which is used to calculate the pseudo-interval travel time.

57 Source: ConeTec Figure 4-16. Example seismic downhole data 4.4.2 In-Hole Logging Methods In-hole logging methods use mechanical, electrical, electromagnetic, nuclear, acoustic (or sonic), and seismic measurements within a borehole (USACE 1995, Hearst et al. 2000, Paillet and Ellefsen 2005). Continuous borehole logs can be made by raising or lowering one or more tools in the borehole, and measurements made by the tools are plotted as a function of depth. With few exceptions, logs cannot be obtained from a cased section of borehole. Borehole logs can be correlated with samples taken from the borehole. Distinctive signatures of subsurface units can be identified on the logs and correlated between holes to generate detailed stratigraphic cross sections of a site. Borehole logging can be used to identify stratified sedimentary deposits such as sands, clays, and organic material; to identify rock units containing radioactive material; and to distinguish permeable sands from impermeable sands. 4.4.2.1 Mechanical Methods Caliper logs are logs of the mechanically or acoustically measured diameter of the borehole and represent one of the most useful and simplest techniques used in borehole geophysics. Mechanical calipers consist of a downhole probe with one or more feeler arms that contact the borehole walls and can detect irregularities on the walls as the probe is pulled up the hole. Mechanical calipers may be used in holes filled with air, water, or drilling fluid. Acoustic calipers consist of a probe usually containing transducers that emit acoustic waves and measure the travel times of the waves reflected from the borehole walls. Borehole diameters can be calculated if the seismic wave velocity in the borehole fluid is known. As such, acoustic calipers must

58 be used in boreholes that are filled with water or drilling fluid. Caliper logs may be used to detect fractures and are commonly used to correct other in-hole logs for borehole diameter effects. 4.4.2.2 Electrical and Electromagnetic Methods Borehole resistivity methods are similar to surface electrical surveys in that electrical current is imparted to subsurface formations, and voltage drops across the formations are measured. Single-point resistance logging consists of a single electrode in the borehole and a single electrode on the ground surface, both of which serve as current and potential electrodes. Normal-resistivity logging is a common multielectrode technique in which multiple current and potential electrodes are contained within the tool itself. The calculated apparent resistivity is sensitive to mineralogy, porosity, chemistry of the pore fluids, degree of saturation, and moisture content as discussed in Section 4.3.2. Spontaneous potential methods measure the electrical potentials established between formation fluids and the drilling fluid and the electrical potentials established at the boundaries of permeable subsurface layers. In both cases, the electrical potential is due to differences in the salinity across formational boundaries or between the formation fluids and drilling fluids. In many boreholes drilled for engineering purposes, natural formation waters are used as the drilling fluids and salinity differences between drilling fluids and formation fluids will not exist, limiting the usefulness of the spontaneous potential log. Similar to surface electromagnetic methods, induction logging uses a time-varying magnetic field generated by a current in a transmitting coil to induce eddy currents in the materials surrounding the borehole. In turn, the eddy currents create a secondary magnetic field that results in a voltage measured by the receiving coil. Induction logs measure conductivity, which is the reciprocal of resistivity. The measurement of conductivity usually is inverted to provide curves of both resistivity and conductivity. 4.4.2.3 Nuclear Methods Nuclear methods involve measuring natural gamma radiation in a formation or the backscatter of radiation as the result of bombardment of the formation by gamma radiation or neutrons. Natural gamma logs measure the natural radioactivity (due to the presence of potassium, thorium, and uranium) of geologic materials and are primarily used for lithologic identification. The natural radioactivity of a material (measured in counts per second) is proportional to the amount of clay minerals present, and, thus, the natural gamma log is ideal for identifying the presence of clay layers and seams. An example of a natural gamma log is shown in Figure 4-17. Also shown in Figure 4-17 are the results of the mechanical caliper and acoustic televiewer (discussed subsequently) logs.

59 Source: Geosyntec Consultants, Inc. Figure 4-17. Example mechanical caliper, natural gamma, and acoustic televiewer logs Gamma-gamma density logs use gamma radiation emitted from a source within the logging tool. As the gamma radiation passes through the formation, some of it is backscattered and measured by a detector in the tool. The degree of gamma radiation backscatter is directly proportional to the bulk density of a material. Neutron porosity logs are made with a source of neutrons in the probe and detectors that measure the backscatter from materials near the borehole. The degree of backscatter is proportional to the amount of hydrogen present, which is largely a function of the water content. In saturated materials, the water content is in turn a function of the porosity.

60 A disadvantage of gamma-gamma density and neutron porosity logs is that the radioactive sources present a health hazard and require permits and certification for transportation and handling. Some states also restrict their use when testing in drinking water aquifers. 4.4.2.4 Optical and Acoustic Televiewer Methods Optical and acoustic televiewers provide a continuous, 360° view of the borehole wall that allows rock mass discontinuities to be identified and characterized. Both devices can be oriented within the borehole so that the absolute orientation of features (e.g., bedding planes) can be measured. An optical televiewer (OTV) uses a camera to record high-resolution images of the borehole wall and includes lights for illumination. An OTV is best suited for dry boreholes or boreholes filled with clear water. Any conditions that produce cloudy or murky water or coatings on the borehole wall limit the usefulness of the OTV. If good images are obtained, it is possible to identify locations and orientations of joints, bedding planes, foliations, faults, shears, and other naturally occurring rock mass discontinuities. The acoustic televiewer (ATV) uses ultrasound pulses from a rotating sensor in an open, fluid-filled borehole to record the amplitude and travel time of the signals reflected at the (high-impedance) interface between fluids and the borehole wall. Because an ATV uses ultrasound rather than visible light, the borehole fluid is not required to be clear. Rock mass discontinuities in the wall of the borehole will change the amplitude of the reflected acoustic wave compared to the surrounding material. The method does not work well in soil because of the lack of a high-impedance boundary between the fluid and soil. ATV surveys are used to provide information regarding locations and orientations of joints, bedding planes, faults, shears, and other naturally occurring rock mass discontinuities. General geologic structure data derived from OTV and ATV data includes a structure log, arrow plot (tadpole), and stereonet plots (polar and rose). An example of travel time and ATV logs is shown in Figure 4-17. The corresponding interpretation of the data is shown in Figure 4-18, which includes the structure, tadpole, and 3D logs. Williams and Johnson (2004) provide a summary of optical and acoustic televiewers and describe how they may be combined and integrated with other in-hole logging methods.

61 Source: Geosyntec Consultants, Inc. Figure 4-18. Example interpretation of acoustic televiewer log 4.4.2.5 Seismic Methods The purpose of seismic logging methods is to measure the compression and shear wave velocity profiles using a tool containing both the source(s) and receivers suspended in a fluid-filled borehole. The borehole fluid provides the necessary coupling between the tool and the surrounding soil or rock. Compression and shear wave velocity are measured at frequent depth intervals (2 ft [0.6 m] or less) as the probe is lowered (or raised) in the borehole. In the geophysical literature, these methods are also often called acoustic or sonic methods. Herein, the term seismic is used to indicate that the primary use is measuring seismic wave velocity profiles. Seismic logging methods offer excellent resolution, and they are well suited for measuring seismic wave velocity profiles at great depths.

62 Early geophysical applications of seismic logging methods focused on measuring only the travel time of compression waves. Since the 1980s, it has been more common to use full waveform logging methods that compression, shear, and Stonely waves to be measured to gather more information. Stonely waves are surface waves that propagate along the interface between the borehole wall and borehole fluid. Full waveform methods usually use logging tools with multiple receivers to enable robust processing methods to be used to calculate seismic wave velocities and amplitudes from the recorded waveforms. A key distinction for geotechnical applications is the type of source used in the logging tool. Most early versions of the tool employed a monopole source, which generates a compression wave in the borehole fluid. Such devices are useful for evaluating fast formations, defined as follows: , > , where , = the shear wave velocity of the formation , = the compression wave velocity of the borehole fluid In a fast formation, it is possible to measure the shear wave velocity of the soil or rock directly because the high-frequency monopole P-wave partitions to P and S waves at the interface between the borehole fluid and borehole wall and are critically refracted along the borehole wall to one or more receivers. Geotechnical applications typically involve slow formations ( , < , ). In such cases, there is no critical refraction of shear waves, and, thus, it is not possible to directly measure the shear wave of the soil using a monopole source. Although the shear wave velocity may be inferred from an analysis of the dispersion of Stonely waves, it is preferable to use a dipole source in slow formations. A dipole source generates compression, shear, and flexural waves along the borehole, enabling direct measurement of the shear wave velocity. The most commonly used variant of seismic logging used for geotechnical site investigations is the P-S suspension log. Figure 4-19 shows an example of compression and shear wave velocity profiles obtained from seismic logging using a dipole-source tool.

63 Source: Geosyntec Consultants, Inc. Figure 4-19. Example results from seismic logging 0 2000 4000 6000 8000 Velocity (ft/sec) 1600 1200 800 400 0 D ep th (f t)

64 Chapter 4 References AASHTO. 2011. AASHTO Guide Specifications for LRFD Seismic Bridge Design. Second Edition, with 2012, 2014, and 2015 Interim Revisions. American Association of State Highway and Transportation Officials, Washington, DC. AASHTO. 2017. AASHTO LRFD Bridge Design Specifications. US Customary Units, Eighth Edition. American Association of State Highway and Transportation Officials, Washington, DC. Allen, F.A., F.E. Richart, Jr., and R.D. Woods. 1980. “Fluid Wave Propagation in Saturated and Nearly Saturated Sands.” Journal of Geotechnical Engineering, Vol. 106, No. GT3, pp. 235–254. Anderson, N., N. Croxton, R. Hoover, and P. Sirles. 2008. Geophysical Methods Commonly Employed for Geotechnical Site Characterization. Transportation Research Circular E-C130, Transportation Research Board, Washington, DC. Bourbie, T., O. Coussy, and B. Zinszner. 1987. Acoustics of Porous Media. Gulf Publishing Company. Caterpillar Inc. 2000. Handbook of Ripping. Twelfth Edition, Peoria, Illinois. Corwin, R.F. 1990. “The Self-Potential Method for Environmental and Engineering Applications.” in Geotechnical and Environmental Geophysics, Vol. I: Review and Tutorial. Ward, S.H., (ed)., Society of Exploration Geophysicists, Tulsa, OK, pp. 127–145. Decker, J.B., K.M. Rollins, and J.C. Ellsworth. 2008. “Corrosion Rate Evaluation and Prediction for Piles Based on Long- Term Field Performance.” Journal of Geotechnical Engineering, Vol. 134, No. 3, pp. 341–351. Ewing, W.M., W.S. Jardetzky, and F. Press. 1957. Elastic Waves in Layered Media, McGraw-Hill, New York. Fenning, P.J., and S. Hasan. 1995. “Pipeline Route Investigations Using Geophysical Techniques.” in Eddleston, M., S. Walthall, S. Cripps, and M.G. Culshaw, (eds), Engineering Geology of Construction, Geological Society Engineering Geology, Special Publication No. 10, pp. 229–233. FHWA. 2002. Subsurface Investigations – Geotechnical Site Characterization. Publication No. FHWA NHI-01-031, Federal Highway Administration, Washington, DC. FHWA. 2006. Soils and Foundations, Reference Manual – Volume I. Publication No. FHWA NHI-06-088, Federal Highway Administration, Washington, DC. Foti, S., C.G. Lai, G.J. Rix, and C. Strobbia. 2015. Surface Wave Methods for Near-Surface Site Characterization. CRC Press, Boca Raton, FL. Foti, S., F. Hollender, F. Garofalo, et al. 2018. “Guidelines for the Good Practice of Surface Wave Analysis: A Product of the InterPACIFIC Project,” Bulletin of Earthquake Engineering, Vol. 16, p. 2367. Hearst, J.R., P.H. Nelson, and F.L. Paillet. 2000. Well Logging for Physical Properties: A Handbook for Geophysicists. Geologists, and Engineers, Second Edition, Wiley and Sons, New Jersey. Hunter, J.A., S.E. Pullan, R.A. Burns, R.M. Gagne, and R.L. Good. 1984. “Shallow Seismic Reflection Mapping of the Overburden‐Bedrock Interface with the Engineering Seismograph—Some Simple Techniques.” Geophysics, Vol. 49, No. 8, pp. 1381–1385. ICE. 1976. Manual of Applied Geology for Engineers. Institution of Civil Engineers, London. Jansen, J., N. Billington, F. Snider, and P. Jurcek. 1994. “Marine SP Surveys for Dam Seepage Investigations: Evaluation of Array Geometries through Modeling and Field Trials.” Proceedings of 7th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems, Boston, Massachusetts, pp. 1053–1071. Long, L.T., and R.D. Kaufmann. 2013. Acquisition and Analysis of Terrestrial Gravity Data. Cambridge University Press, New York, New York. Louie, J.N. 2001. “Faster, Better: Shear-Wave Velocity to 100 Meters Depth from Refraction Microtremor Arrays.” Bulletin of the Seismological Society of America, Vol. 91, No. 2, pp. 347–364. Mavko, G., T. Mukerji, and J. Dvorkin. 1998. The Rock Physics Handbook: Tools for Seismic Analysis in Porous Media. Cambridge University Press, Cambridge, United Kingdom. McNeill, J.D. 1990. “Use of Electromagnetics for Groundwater Studies,” Geotechnical and Environmental Geophysics. Vol. I: Review and Tutorial, Ward, S.H., (ed)., Society of Exploration Geophysicists, Tulsa, OK, pp. 191–218. Miller, R.D., and D.W. Steeples. 2008. High-Resolution Seismic-Reflection Imaging of I-70 Sinkholes, Russell County, Kansas. Kansas Department of Transportation, Open-File Report 2008-18, October.

65 Morey, R.M. 1998. Ground Penetrating Radar for Evaluating Subsurface Conditions for Transportation Facilities. National Cooperative Highway Research Program Synthesis 255, National Cooperative Highway Research Program, National Academy of Science, Washington, DC. Paillet, F.L., and K.J. Ellefsen. 2005. “Downhole Applications of Geophysics.” Near-Surface Geophysics, Butler, D.K., (ed). Society of Exploration Geophysicists, Tulsa, Oklahoma, pp. 439–471. Palmer, D. 1981. “An Introduction to the Generalized Reciprocal Method of Seismic Refraction Interpretation.” Geophysics, Vol. 46, No. 11, pp. 1508–1518. Pugin, A.J.M., S. Pullan, J.A. Hunter, and G.A. Oldenborger. 2009. “Hydrogeological Prospecting Using P- and S-Wave Landstreamer Seismic Reflection Methods.” Near Surface Geophysics, pp. 315–327. Santamarina, J.C., K.A. Klein, and M.A. Fam. 2001. Soils and Waves: Particulate Materials Behavior, Characterization, and Process Monitoring. Wiley and Sons, West Sussex, United Kingdom. Sirles, P. 2006. Use of Geophysics for Transportation Projects. National Cooperative Highway Research Program Synthesis 357, Transportation Research Board, Washington, DC. Steeples, D.W., and R.D. Miller. 1990. “Seismic Reflection Methods Applied to Engineering, Environmental, and Groundwater Problems.” in S.H. Ward, (ed), Geotechnical and Environmental Geophysics, Society of Exploration Geophysics, 63, 1–30. USACE. 1995. Geophysical Exploration for Engineering and Environmental Investigations. Engineer Manual 1110-1-1802, U.S. Army Corps of Engineers, Washington, DC. White, D. J. 1989. “Two-Dimensional Seismic Refraction Tomography.” Geophysical Journal International, Vol. 97, No. 2, pp. 223–245. Wightman, W.E., F. Jalinoos, P. Sirles, and K. Hanna. 2003. Application of Geophysical Methods to Highway Related Problems. Report FHWA-IF-04-021, Federal Highway Administration, Washington, DC. Williams, J.H. and C.D. Johnson. 2004. “Acoustic and Optical Borehole-Wall Imaging for Fractured-Rock Aquifer Studies.” Journal of Applied Geophysics, Vol. 55, Issue 1-2, pp. 151–159. Zhang, J., and M. Toksoz. 1998. “Nonlinear Refraction Traveltime Tomography.” Geophysics, Vol. 63, No. 5, pp. 1726– 1737. Zonge, K., J. Wynn, and S. Urquhart. 2005. “Resistivity, Induced Polarization, and Complex Resistivity.” in Near-Surface Geophysics, Butler, D.K., (ed), Society of Exploration Geophysicists, Tulsa, Oklahoma, pp. 265–300.

TRB's National Cooperative Highway Research Program (NCHRP) Web-Only Document 258: Manual on Subsurface Investigations provides an update to the American Association of State Highway Transportation Officials (AASHTO) 1988 manual of the same name. This report reflects the changes in the approaches and methods used for geotechnical site characterization that the geotechnical community has developed and adopted in the past thirty years. The updated manual provides information and guidelines for planning and executing a geotechnical site investigation program. It may also be used to develop a ground model for planning, design, construction, and asset management phases of a project.

READ FREE ONLINE

Welcome to OpenBook!

You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

Do you want to take a quick tour of the OpenBook's features?

Show this book's table of contents , where you can jump to any chapter by name.

...or use these buttons to go back to the previous chapter or skip to the next one.

Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

To search the entire text of this book, type in your search term here and press Enter .

Share a link to this book page on your preferred social network or via email.

View our suggested citation for this chapter.

Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

Get Email Updates

Do you enjoy reading reports from the Academies online for free ? Sign up for email notifications and we'll let you know about new publications in your areas of interest when they're released.

• Engineering Geology
• Field Methods
• Historical Geology
• Hydrogeology
• Earth Interior
• Geologic Time Scale
• Plate Tectonics
• Geologic Lists
• Geological Wonders
• Igneous Rocks
• Extrusive Igneous Rocks
• Intrusive Igneous Rocks
• Metamorphic Rocks
• Foliated Metamorphic Rocks
• Sedimentary Rocks
• Metamorphic rocks
• Borate minerals
• Carbonates Minerals
• Halide Minerals
• Native Mineral
• Physical Properties
• Optical Properties
• Earthquakes
• Volcanic Eruption
• Privacy Policy

The Seismic Method

The seismic method is a crucial technique in geophysics that plays a significant role in understanding the subsurface structure of the Earth. It is widely employed in various fields such as oil and gas exploration, environmental studies, civil engineering, and geological research. Seismic methods involve the use of artificially generated seismic waves and their interaction with subsurface materials to create detailed images of the Earth’s interior.

The seismic method is a geophysical technique that utilizes the propagation of seismic waves through the Earth to gather information about its subsurface structure. Seismic waves can be artificially generated by various means, including striking the ground with a heavy weight, detonating explosives, or using specialized vibrational sources. These waves travel through the Earth and are recorded by sensors (geophones or accelerometers) at the surface or in boreholes.

The recorded data is then processed and analyzed to create seismic images, providing valuable insights into the composition, density, and geometry of subsurface layers. The seismic method is based on the principle that seismic waves travel at different velocities through different types of rocks and geological formations.

Importance in Geophysics and Exploration:

• Subsurface Imaging: Seismic methods are essential for creating detailed images of the subsurface, helping geophysicists and geologists understand the distribution of rocks, sediments, and other geological features. This information is crucial for a wide range of applications, including resource exploration and environmental assessments.
• Hydrocarbon Exploration: In the oil and gas industry, seismic surveys are fundamental for locating potential hydrocarbon reservoirs beneath the Earth’s surface. By analyzing the reflected seismic waves, exploration teams can identify structures that may contain oil and gas deposits .
• Civil Engineering: Seismic methods are employed in civil engineering to assess the geological conditions of a site before construction. This helps engineers understand potential risks related to earthquakes and design structures that can withstand seismic forces.
• Environmental Studies: Seismic techniques are used in environmental studies to investigate subsurface conditions, including groundwater aquifers , soil properties, and potential contamination. This information is critical for environmental impact assessments and remediation projects.
• Natural Hazard Assessment: Seismic methods are vital for studying and monitoring natural hazards such as earthquakes and volcanic activity. Understanding the subsurface structure and fault lines helps in assessing seismic risks and implementing measures to mitigate potential disasters.

In summary, the seismic method is a versatile and powerful tool in geophysics and exploration, providing valuable information about the Earth’s subsurface for a wide range of applications across various industries.

Basic Principles of Seismic Method

Seismic instruments and equipment, seismic data acquisition, seismic data processing, applications of seismic method.

The seismic method relies on the principles of seismic wave propagation through the Earth’s subsurface. These waves are generated artificially and then recorded to create images of the subsurface structure. The basic principles of the seismic method include:

• Generation of Seismic Waves: Seismic waves are typically generated by a controlled source, which could be a weight dropped on the ground, explosives, or a specialized vibrational device. The goal is to create a disturbance that produces waves capable of penetrating the Earth.
• Propagation of Seismic Waves: Once generated, seismic waves travel through the Earth, penetrating different layers and reflecting back to the surface at interfaces where there are changes in subsurface properties, such as rock types or geological structures. The two main types of seismic waves are compressional waves (P-waves) and shear waves (S-waves), each with distinct properties and velocities.
• Recording Seismic Waves: Seismic waves are recorded by sensors known as geophones or accelerometers, which are strategically placed on the Earth’s surface or in boreholes. These sensors detect ground motion caused by the seismic waves passing through the subsurface.
• Travel Time Analysis: The recorded data, known as seismic traces, are analyzed to determine the arrival times of seismic waves at different receivers. By measuring the travel times and understanding the velocity of the waves, geophysicists can infer the depth and properties of subsurface structures.
• Velocity Variation and Layering: Seismic waves travel at different velocities through different materials. This variation in velocity is used to distinguish between various subsurface layers and geological formations. The analysis considers both the vertical and lateral distribution of materials.
• Reflection and Refraction: Reflections occur when seismic waves encounter a boundary between two layers with different acoustic properties. Refractions occur when waves change direction due to variations in subsurface velocity. Both reflection and refraction data are crucial for constructing detailed images of the subsurface.
• Data Processing and Imaging: Seismic data undergoes extensive processing to enhance signal quality, remove noise, and convert it into a meaningful representation of the subsurface. Advanced imaging techniques, such as seismic tomography and migration, are employed to create detailed three-dimensional models.
• Interpretation: Geoscientists interpret the processed seismic images to identify geological structures, such as faults , folds , and stratigraphic layers. This interpretation provides valuable information for applications like resource exploration, environmental studies, and geological mapping.

By applying these basic principles, the seismic method allows geophysicists and geologists to gain insights into the Earth’s subsurface, enabling a better understanding of geological features and supporting various scientific and industrial applications.

Seismic surveys rely on specialized instruments and equipment to generate seismic waves, record the resulting data, and analyze the subsurface structure. Here are key seismic instruments and equipment used in the seismic method:

• Explosive Charges: Controlled explosions, often using dynamite or other explosives, are used to generate powerful seismic waves.
• Vibrators: Specialized trucks equipped with vibrational devices generate seismic waves by vibrating the ground. These are commonly used in urban areas or environmentally sensitive locations.
• Geophones are sensors placed on the ground surface or in boreholes to detect ground motion caused by seismic waves.
• They convert ground vibrations into electrical signals, which are recorded for further analysis.
• Geophones come in various designs, including vertical and horizontal components, depending on the type of seismic waves being measured.
• Similar to geophones, accelerometers measure ground acceleration during seismic events.
• They are often used in structural monitoring and can be more sensitive than traditional geophones.
• Seismic sensors are connected by cables to a central recording unit.
• The layout of these sensors, known as the spread, determines the geometry of the seismic survey and influences the quality of the data.
• Seismic Recorders: These electronic devices record the signals from geophones or accelerometers.
• Data Acquisition Systems: These systems collect and store the recorded data for later processing.
• Modern recording systems use digital technology, allowing for more efficient data handling and storage.
• In marine seismic surveys, air guns are often used as the energy source.
• These devices release compressed air into the water, creating underwater acoustic waves that penetrate the seafloor and provide information about subsurface structures beneath the ocean floor.
• Accurate positioning is crucial for seismic surveys, especially in marine environments.
• GPS (Global Positioning System) and inertial navigation systems help ensure precise location data for each recorded seismic trace.
• Specialized software is used to process and analyze seismic data.
• Processing steps include filtering, stacking, migration, and inversion to enhance the quality and interpretability of seismic images.
• In some cases, interpolation tools are used to fill in the gaps between seismic lines, creating a more comprehensive image of the subsurface.
• In borehole seismology, equipment such as drilling rigs and casing materials are used to create boreholes for the placement of geophones or accelerometers at depth.

These instruments and equipment work together to collect and process seismic data, providing valuable insights into the subsurface structure for applications ranging from oil and gas exploration to environmental studies and geological research.

Seismic data acquisition is a critical step in the seismic method, involving the collection of measurements from seismic sensors to create a detailed image of the Earth’s subsurface. The process typically includes the following key steps:

• Before acquiring seismic data, geophysicists design a survey plan to determine the layout of seismic sources and receivers.
• Factors such as the desired resolution, depth of investigation, and the nature of the subsurface influence the survey design.
• Seismic sources, whether explosive charges or vibrational devices, are deployed according to the survey design.
• Explosive charges are strategically placed on the ground or within boreholes, while vibrators are mounted on specialized trucks.
• Geophones or accelerometers are placed in a predetermined pattern, known as the spread.
• The spread configuration influences the geometry of the survey and affects the quality of the acquired data.
• Seismic sensors (geophones or accelerometers) are connected to recording units via cables. The recording units may be distributed across the survey area.
• The recording setup is designed to capture the arrival times and amplitudes of seismic waves at each sensor location.
• Seismic data acquisition involves activating the seismic sources to generate waves that propagate through the subsurface.
• The sensors detect the ground motion caused by the seismic waves, and the resulting signals are converted into electrical data.
• Precise timing and synchronization are crucial for accurate data interpretation.
• A master clock is used to ensure that seismic sources and sensors are triggered simultaneously, allowing for accurate measurement of wave arrival times.
• Real-time quality control measures are implemented during data acquisition to identify and address issues promptly.
• This may include checking for sensor malfunctions, cable connectivity, and ensuring proper source activation.
• For land surveys, GPS systems are used to accurately position seismic sources and receivers.
• In marine surveys, additional navigation systems, such as inertial navigation, are employed to ensure precise positioning in the dynamic marine environment.
• Seismic recorders or data acquisition systems collect and store the recorded data for subsequent processing.
• Modern systems use digital recording, allowing for efficient storage, retrieval, and analysis of large volumes of data.
• In some applications, such as reservoir monitoring in the oil and gas industry, seismic surveys are repeated over time to observe changes in the subsurface (4D seismic). This provides insights into reservoir dynamics.

After seismic data acquisition, the recorded data undergoes extensive processing to enhance its quality and extract valuable information about the subsurface structure. Advanced imaging techniques are then applied to create detailed three-dimensional models for interpretation and analysis.

Seismic data processing is a crucial step in the seismic method that involves the application of various techniques to enhance the quality, accuracy, and interpretability of the recorded seismic data. The goal is to create detailed images of the subsurface structure for geological interpretation and exploration. The seismic data processing workflow typically includes the following key steps:

• The first step involves checking the quality of the data collected during the seismic survey.
• Quality control measures address issues such as sensor malfunctions, cable problems, and any other anomalies that may affect data accuracy.
• Timing Corrections: Adjustments are made to correct for variations in timing, ensuring that seismic events are accurately synchronized.
• Gain Correction: The recorded seismic traces may undergo gain corrections to account for variations in source-receiver distances and sensor sensitivities.
• Various filters are applied to the seismic data to remove unwanted noise and enhance the signal of interest.
• Common filters include bandpass filters to isolate specific frequency ranges and eliminate noise.
• Deconvolution is a process that aims to sharpen seismic wavelets and improve resolution.
• It is particularly useful in removing the effects of the seismic source from the recorded data.
• Velocity analysis is performed to estimate the subsurface velocity profile.
• Different velocities of seismic waves through different subsurface materials can affect the recorded seismic data.
• NMO correction is applied to correct for the curvature of seismic events caused by variations in subsurface velocities.
• This correction helps to align events in the seismic data and produce a more accurate representation of subsurface structures.
• Stacking involves combining multiple seismic traces to improve signal-to-noise ratio.
• It enhances the overall quality of the seismic data and increases the reliability of subsurface imaging.
• Migration is a critical step that corrects for the distortions in the position of subsurface reflections caused by the complex geometry of the Earth’s subsurface.
• Common migration techniques include time migration and depth migration.
• Additional processing steps may be applied after stacking to further enhance the seismic data.
• These steps may include amplitude corrections, frequency balancing, and other adjustments to improve the overall quality of the seismic image.
• Inversion techniques are employed to transform seismic data into quantitative subsurface properties, such as acoustic impedance.
• This step provides more detailed information about the subsurface composition and facilitates geological interpretation.
• Geoscientists interpret the processed seismic data to identify geological features, including faults, stratigraphic layers, and potential hydrocarbon reservoirs.

Seismic data processing is a complex and iterative process that requires expertise in signal processing and geophysics. Advanced algorithms and computational methods are used to handle large volumes of data and produce accurate and high-resolution images of the Earth’s subsurface. The processed data serves as a valuable tool for decision-making in various industries, including oil and gas exploration, environmental studies, and geotechnical investigations.

The seismic method finds diverse applications across various scientific, industrial, and environmental fields. Some of the key applications include:

• Seismic surveys are extensively used in the oil and gas industry to locate potential hydrocarbon reservoirs beneath the Earth’s surface.
• The method helps identify subsurface structures, map geological formations, and estimate the size and characteristics of potential reservoirs.
• Seismic methods are employed in mineral exploration to characterize the subsurface and identify potential ore bodies.
• The technique helps in mapping geological structures, determining rock types, and assessing the composition of the Earth’s crust.
• Seismic surveys are used for environmental and engineering applications, including assessing subsurface conditions for construction projects.
• The method helps evaluate soil properties, identify potential geological hazards, and assess groundwater resources.
• Seismic studies are crucial in civil engineering for evaluating the geological conditions of a site before construction.
• The method helps assess the seismic risk of an area, design structures that can withstand earthquakes, and plan infrastructure projects.
• Seismic methods are employed in the exploration of geothermal resources to identify subsurface structures and assess the potential for geothermal energy extraction.
• Seismic surveys are used to investigate subsurface conditions and locate potential groundwater aquifers.
• Understanding the geological formations helps in sustainable groundwater management and resource planning.
• Seismic methods play a crucial role in assessing and monitoring natural hazards such as earthquakes, landslides , and volcanic activity.
• The information gathered helps in understanding the subsurface dynamics and potential risks associated with these hazards.
• Seismic surveys are used in CCS projects to monitor the injection and storage of carbon dioxide in underground reservoirs.
• The method helps ensure the integrity of storage sites and assess the potential for leakage.
• Seismic methods are applied in archaeological studies to non-invasively explore subsurface structures and detect buried archaeological features.
• This can aid in the preservation and documentation of cultural heritage sites.
• In the oil and gas industry, repeated seismic surveys (4D seismic) are conducted to monitor changes in reservoir properties over time.
• This helps optimize production strategies, assess reservoir performance, and identify potential production issues.
• Seismic studies contribute to understanding the Earth’s tectonic processes, fault systems, and earthquake mechanisms.
• This information is vital for seismic hazard assessments and earthquake preparedness.

The seismic method’s versatility makes it a valuable tool in various disciplines, providing essential insights into the Earth’s subsurface for scientific research, resource exploration, and environmental management.

RELATED ARTICLES MORE FROM AUTHOR

Electromagnetic (em) methods, ground-penetrating radar (gpr), electrical resistivity surveys, magnetic surveys, gravity surveys, geophysical methods, recent posts, mount ruang, fossil coral.

• My presentations

Auth with social network:

Download presentation

We think you have liked this presentation. If you wish to download it, please recommend it to your friends in any social system. Share buttons are a little bit lower. Thank you!

Presentation is loading. Please wait.

To view this video please enable JavaScript, and consider upgrading to a web browser that supports HTML5 video

GEOPHYSICAL APPLICATIONS FOR GENERAL EXPLORATION

Published by Zoe Morrison Modified over 8 years ago

Similar presentations

Presentation on theme: "GEOPHYSICAL APPLICATIONS FOR GENERAL EXPLORATION"— Presentation transcript:

National Geofund and Geology (NGG)

Begin $100 $200 $300 $400 $500 Earth & SpacePhysicalScience ENERGY & LIGHT Geology & Geography Matter & More!ANIMALS.

Large Scale Mapping of Groundwater Resources Using a Highly Integrated Set of Tools Verner H. Søndergaard Geological Survey of Denmark and Greenland, Denmark.

Electromagnetic Waves

Scientists divide the Earth

Michael Kaminski  Team Leader  Endor Upstream Technology Directorate David Pelly  Technology Team Leader  Upstream Technology Group.

AKS Geoscience. Located in Calgary, Alberta, Canada, AKS Geoscience Inc. is a progressive independent firm comprised of professional.

The Oil & Gas Industry Our activities in Uganda Drilling The Geology team EHS 1. Where does Oil and Gas come from? 1. Source Rocks – THE INGREDIENTS FOR.

Magnetic Expression of Buried and Obscured Anticlines in South America An HRAM survey flown over a tropical forest in Guatemala reveals the presence of.

The Future of Mineral Supplies To know a range of methods which may be used to extend the time period in which mineral supplies may be exploited.

Seismic Refraction Method for Groundwater Exploration Dr. A K Rastogi Professor, Dept. of Civil Engineering I I T Bombay.

Applied Geophysics An Introduction

Overview of Environmental Geology

PETROLEUM GEOSCIENCE PROGRAM Offered by GEOPHYSICS GEOPHYSICS DEPARTMENT IN COROPORATION WITH GEOLOGY, PHYSICS, CHEMISTRY, AND MATHEMATICS DEPARTMENTS.

Petroleum Exploration

Methods of Exploration. Methods of Mineral Exploration The most common methods of mineral exploration are: Aerial methods – magnetic, gravity and electromagnetic.

EXPLORATION OF MINERAL DEPOSIT. AREA SELECTION Area selection is the most crucial part of mineral exploration. Selecting the most suitable area, geological.

Geophysical and Geochemical Exploration Techniques  The specification sates that you should be able to:  Describe the geophysical exploration techniques.

Applied Geophysics Geology 319 / 829

Basic Geologic and Hydrogeologic Investigations

About project

© 2024 SlidePlayer.com Inc. All rights reserved.

'Geophysical methods' presentation slideshows

Geophysical methods - powerpoint ppt presentation.

Rainfall Records

Rainfall Records. Professor Steve Kramer. Rainfall Records. Measured at single point by rain gauge Over extended period of time, can establish: Mean annual rainfall Standard deviation of annual rainfall. Mean + s. Mean. Mean - s. Rainfall Records.

1.1k views • 83 slides

G7481 Magnetometry in geology and archaeology

386 views • 27 slides

Magnetism and Sea-Floor Spreading

Magnetism and Sea-Floor Spreading. OCEA/ERTH 4110/5110. Introduction to Marine Geology. 1. Introduction and Definitions. typical hand compass only measures declination d , i.e. angle between horizontal field (H) and true north (spin axis). Components of a Vector Magnetic Field.

370 views • 19 slides

287 views • 17 slides

Field Methods and Groundwater Models

Field Methods and Groundwater Models. Field Methods. Hydrogeologists can apply field methods in exploration for groundwater supplies and various aspects of environmental hydrogeology.

177 views • 16 slides

GIS in Geology

285 views • 8 slides

Unit 3: The Geosphere

Troy Gyant. Unit 3: The Geosphere. WWK. How scientists use geophysical methods, new conceptual interpretations of data and analysis of geography to study the geosphere. Who studies the Geosphere?. The Geosphere is studied by Geologists and Geophysicists .

300 views • 7 slides

PRINCIPLES OF GEOPHYSICS

PRINCIPLES OF GEOPHYSICS. Introduction. Geophysics is an interdisciplinary physical science concerned with the nature of the earth and its environment

2.03k views • 6 slides

218 views • 1 slides

View Geophysical methods PowerPoint (PPT) presentations online in SlideServe. SlideServe has a very huge collection of Geophysical methods PowerPoint presentations. You can view or download Geophysical methods presentations for your school assignment or business presentation. Browse for the presentations on every topic that you want.

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

• View all journals
• Explore content
• About the journal
• Publish with us
• Sign up for alerts
• Review Article
• Published: 10 June 2024

Liquid-metal experiments on geophysical and astrophysical phenomena

• Frank Stefani   ORCID: orcid.org/0000-0002-8770-4080 1  

Nature Reviews Physics ( 2024 ) Cite this article

229 Accesses

3 Altmetric

Metrics details

• Astronomy and planetary science
• Planetary science

Recent decades have seen enormous progress in the experimental investigation of fundamental processes that are relevant to geophysical and astrophysical fluid dynamics. Liquid metals have proven particularly suited for such studies, partly owing to their small Prandtl numbers that are comparable to those in planetary cores and stellar convection zones, partly owing to their high electrical conductivity that allows the study of various magnetohydrodynamic phenomena. After introducing the theoretical basics and the key dimensionless parameters, we discuss some of the most important liquid-metal experiments on Rayleigh–Bénard convection, Alfvén waves, magnetically triggered flow instabilities such as the magnetorotational and Tayler instability, and the dynamo effect. Finally, we summarize what has been learned so far from those recent experiments and what could be expected from future ones.

Geophysical and astrophysical fluid dynamics is concerned with diverse phenomena as convection and magnetic field generation in stellar and planetary interiors or accretion onto protostars and black holes.

Liquid-metal experiments are suited for investigating these processes, partly owing to their high electrical conductivity and partly owing to their small Prandtl numbers that are comparable to those in planetary cores and stellar convection zones.

Apart from heat transport scalings, liquid-metal convection experiments have explored a wide variety of flow structures that occur in dependence on the geometric aspect ratio and the presence of magnetic fields.

Exposing liquid rubidium to a high-pulsed magnetic field has allowed to equalize the speeds of Alfvén waves and sound waves and to study their mutual transformation that is a key ingredient for heating the solar corona.

The past decades have seen enormous progress in the experimental realization of the hydromagnetic dynamo effect and of various forms of the magnetorotational instability.

This is a preview of subscription content, access via your institution

Access options

Access Nature and 54 other Nature Portfolio journals

Get Nature+, our best-value online-access subscription

24,99 € / 30 days

cancel any time

Subscribe to this journal

Receive 12 digital issues and online access to articles

92,52 € per year

only 7,71 € per issue

Buy this article

• Purchase on Springer Link
• Instant access to full article PDF

Prices may be subject to local taxes which are calculated during checkout

Similar content being viewed by others

Stratification in planetary cores by liquid immiscibility in Fe-S-H

Transient variation in seismic wave speed points to fast fluid movement in the Earth's outer core

Gyres, jets and waves in the Earth’s core

Schumacher, J. & Sreenivasan, K. R. Colloquium: unusual dynamics of convection in the Sun. Rev. Mod. Phys. 92 , 041001 (2020).

Article   ADS   MathSciNet   Google Scholar  

Harlander, U. et al. New laboratory experiments to study the large-scale circulation and climate dynamics. Atmosphere 14 , 836 (2023).

Article   ADS   Google Scholar  

Gekelman, W. Review of laboratory experiments on Alfvén waves and their relationship to space observations. J. Geophys. Res. 104 , 14417 (1999).

Le Bars, M. et al. Fluid dynamics experiments for planetary interiors. Surv. Geophys. 43 , 229–261 (2022).

Le Bars, M., Cébron, D. & Le Gal, P. Flows driven by libration, precession, and tides. Ann. Rev. Fluid Mech. 47 , 163–193 (2015).

Rüdiger, G., Hollerbach, R. & Kitchatinov, L. L. Magnetic Processes in Astrophysics: Theory, Simulations, Experiments (Wiley-VCH, 2013).

Rüdiger, G., Gellert, M., Hollerbach, R., Schultz, M. & Stefani, F. Stability and instability of hydromagnetic Taylor–Couette flows. Phys. Rep. 741 , 1–89 (2018).

Ji, H. & Goodman, J. Taylor-Couette flow for astrophysical purposes. Phil. Trans. R. Soc. A 381 , 20220119 (2023).

Rincon, F. Dynamo theories. J. Plasma Phys. 85 , 205850401 (2019).

Article   Google Scholar  

Tobias, S. The turbulent dynamo. J. Fluid Mech. 912 , P1 (2021).

Brandenburg, A., Elstner, D., Masada, Y. & Pipin, V. Turbulent processes and mean-field dynamo. Space Sci. Rev. 219 , 55 (2023).

Gailitis, A., Lielausis, O., Platacis, E., Gerbeth, G. & Stefani, F. Laboratory experiments on hydromagnetic dynamos. Rev. Mod. Phys. 74 , 973–990 (2002).

Stefani, F., Gailitis, A. & Gerbeth, G. Magnetohydrodynamic experiments on cosmic magnetic fields. Zeitschr. Angew. Math. Mech. 88 , 930–954 (2008).

Stefani, F., Giesecke, A. & Gerbeth, G. Numerical simulations of liquid metal experiments on cosmic magnetic fields. Theor. Comp. Fluid Dyn. 23 , 405–429 (2009).

Verhille, G., Plihon, N., Bourgoin, M., Odier, P. & Pinton, J.-F. Laboratory dynamo experiments. Space Sci. Rev. 152 , 543–564 (2010).

Pandey, A., Scheel, J. D. & Schumacher, J. Turbulent superstructures in Rayleigh-Bénard convection. Nat. Commun. 9 , 2118 (2018).

Grant, S. D. T. et al. Alfvén wave dissipation in the solar chromosphere. Nat. Phys. 14 , 480–483 (2018).

Hazra, G., Nandy, D., Kitchatinov, L. & Choudhuri, A. R. Mean field models of flux transport dynamo and meridional circulation in the Sun and stars. Space Sci. Rev. 219 , 39 (2023).

Matilsky, L. I., Hindman, B. W., Featherstone, N. A., Blume, C. & Toomre, J. Confinement of the solar tachocline by dynamo action in the radiative interior. Astrophys. J. Lett. 940 , L50 (2022).

Eggenberger, P., Moyano, F. D. & den Hartogh, J. W. Rotation in stellar interiors: general formulation and an asteroseismic-calibrated transport by the Tayler instability. Astron. Astrophys. 6 , 788–795 (2022).

Google Scholar  

Eggenberger, P. et al. The internal rotation of the Sun and its link to the solar Li and He surface abundances. Nat. Astron. 6 , 788–795 (2022).

Goedbloed, H., Keppens, R. & Poedts, S. Magnetohydrodynamics of Laboratory and Astrophysical Plasmas (Cambridge Univ. Press, 2019).

Cowling, T. G. The magnetic field of sunspots. Mon. Not. Roy. Astr. Soc. 140 , 39–48 (1934).

Kaiser, R. The non-radial velocity theorem revisited. Geophys. Astrophys. Fluid Dyn. 101 , 185–197 (2007).

Schaeffer, N., Jault, D., Nataf, H.-C. & Fournier, A. Turbulent geodynamo simulations: a leap towards Earth’s core. Geophys. J. Int. 211 , 1–29 (2017).

Lehnert, B. in Magnetohydrodynamics — Modern Evolution and Trends 27–36 (Springer, 2007).

Raja, K. K. A study on sodium — the fast breeder reactor coolant. IOP Conf. Ser. Mater. Sci. Eng. 1045 , 012013 (2021).

An, D., Sunderland, P. B. & Lathrop, D. P. Suppression of sodium fires with liquid nitrogen. Fire Saf. J. 58 , 204–207 (2013).

Stefani, F., Forbriger, J., Gundrum, T. H., Herrmannsdörfer, T. & Wosnitza, J. Mode conversion and period doubling in a liquid rubidium Alfvén-wave experiment with coinciding sound and Alfvén speeds. Phys. Rev. Lett. 127 , 275001 (2021).

Morley, N. B., Burris, J., Cadwallader, L. C. & Nornberg, M. D. GaInSn usage in the research laboratory. Rev. Sci. Instrum. 79 , 056107 (2008).

Plevachuk, Y. U., Sklyarchuk, V., Eckert, S., Gerbeth, G. & Novakovic, R. Thermophysical properties of the liquid Ga-In-Sn eutectic alloy. J. Chem. Eng. Data 59 , 757–763 (2014).

Alemany, A., Moreau, R., Sulem, P. L. & Frisch, U. Influence of an external magnetic field on homogeneous MHD turbulence. J. de Mec. 18 , 277–313 (1979).

ADS   Google Scholar  

Sukoriansky, S., Zilberman, I. & Branover, H. Experimental studies of turbulence in mercury flows with transverse magnetic fields. Exp. Fluids 4 , 11–16 (1986).

Cioni, S., Ciliberto, S. & Sommeria, J. Strongly turbulent Rayleigh-Bénard convection in mercury: comparison with results at moderate Prandtl number. J. Fluid Mech. 335 , 111–140 (1997).

Zherlitsyn, S., Wustmann, B., Herrmannsdörfer, T. & Wosnitza, J. Status of the pulsed-magnet-development program at the Dresden High Magnetic Field Laboratory. IEEE Trans. Appl. Supercond. 22 , 4300603 (2012).

Béard, F. & Debray, F. The French high magnetic field facility. J. Low Temp. Phys. 170 , 541–552 (2012).

Wijnen, F. J. P. et al. Design of the resistive insert for the Nijmegen 45 T hybrid magnet. IEEE Trans. Appl. Supercond. 30 , 4300204 (2020).

Nguyen, D. N., Michel, J. & Mielke, C. H. Status and development of pulsed magnets at the NHMFL pulsed field facility. IEEE Trans. Appl. Supercond. 26 , 4300905 (2016).

King, E. M. & Aurnou, J. M. Turbulent convection in liquid metal with and without rotation. Proc. Natl Acad. Sci. USA 110 , 6688–6693 (2013).

Ren, L. et al. Flow states and heat transport in liquid metal convection. J. Fluid Mech. 951 , R1 (2022).

Zürner, T., Schindler, F., Vogt, T., Eckert, S. & Schumacher, J. Combined measurement of velocity and temperature in liquid metal convection. J. Fluid Mech. 876 , 1108–1128 (2019).

Takeda, Y. Measurement of velocity profile of mercury flow by ultrasound Doppler shift method. Nucl. Techn. 79 , 120–124 (1987).

Brito, D., Nataf, H.-C., Cardin, P., Aubert, J. & Masson, J.-P. Ultrasonic Doppler velocimetry in liquid gallium. Exp. Fluids 31 , 653–663 (2001).

Eckert, S. & Gerbeth, G. Velocity measurements in liquid sodium by means of ultrasound Doppler velocimetry. Exp. Fluids 32 , 542–546 (2002).

Eckert, S., Buchenau, D., Gerbeth, G., Stefani, F. & Weiss, F.-P. Some recent developments in the field of measuring techniques and instrumentation for liquid metal flows. J. Nucl. Sci. Techn. 48 , 490–498 (2011).

Eckert, S., Gerbeth, G. & Melnikov, V. I. Velocity measurements at high temperatures by ultrasound Doppler velocimetry using an acoustic wave guide. Exp. Fluids 35 , 381–388 (2003).

Mäder, K. et al. Phased-array ultrasound system for planar flow mapping in liquid metals. IEEE Trans. Ultrason. Ferroelectr. Freq. Control. 69 , 1327–1335 (2017).

Schmitt, D. et al. Rotating spherical Couette flow in a dipolar magnetic field. J. Fluid Mech. 604 , 175–197 (2008).

Ricou, R. & Vives, C. Local velocity and mass transfer measurements in molten metals using an incorporated probe. Int. J. Heat Mass Transf. 25 , 1579–1588 (1982).

Cramer, A., Varshney, K., Gundrum, T. & Gerbeth, G. Experimental study on the sensitivity and accuracy of electric potential local flow measurements. Flow. Meas. Instrum. 17 , 1–11 (2006).

Stefani, F. & Gerbeth, G. A contactless method for velocity reconstruction in electrically conducting fluids. Meas. Sci. Techn. 11 , 758–765 (2000).

Stefani, F., Gundrum, T. H. & Gerbeth, G. Contactless inductive flow tomography. Phys. Rev. E 70 , 056306 (2004).

Hämäläinen, M., Hari, R., Ilmoniemi, R. J., Knuutila, J. & Lounasmaa, O. V. Magnetoencephalography: theory, instrumentation, and applications to noninvasive studies of the working human brain. Rev. Mod. Phys. 65 , 413–497 (1993).

Vogt, T., Horn, S., Grannan, A. M. & Aurnou, J. M. Jump rope vortex in liquid metal convection. Proc. Natl Acad. Sci. USA. 115 , 12674–12679 (2018).

Akashi, M. et al. Transition from convection rolls to large-scale cellular structures in turbulent Rayleigh-Bénard convection in a liquid metal layer. Phys. Rev. Fluids 4 , 033501 (2019).

Grossmann, S. & Lohse, D. Scaling in thermal convection: a unifying theory. J. Fluid Mech. 407 , 27–56 (2000).

Takeshita, T., Segawa, T., Glazier, J. A. & Sano, A. Thermal turbulence in mercury. Phys. Rev. Lett. 76 , 1465–1468 (1996).

Glazier, J. A., Segawa, T., Naert, A. & Sano, M. Evidence against “ultrahard” thermal turbulence at very high Rayleigh numbers. Nature 398 , 307–310 (1999).

Tsuji, Y., Mizuno, T., Mashiko, T. & Sano, M. Mean wind in convective turbulence of mercury. Phys. Rev. Lett. 94 , 034501 (2005).

Khalilov, R. et al. Thermal convection of liquid sodium in inclined cylinders. Phys. Rev. Fluids 3 , 043503 (2018).

Schindler, F., Eckert, S., Zürner, F., Schumacher, J. & Vogt, T. Collapse of coherent large scale flow in strongly turbulent liquid metal convection. Phys. Rev. Lett. 128 , 164501 (2022).

Schindler, F., Eckert, S., Zürner, F., Schumacher, J. & Vogt, T. Collapse of coherent large scale flow in strongly turbulent liquid metal convection. Phys. Rev. Lett. 128 , 164501 (2022); erratum 131 , 159901 (2023).

Verzicco, R. & Camussi, R. Transitional regimes of low-Prandtl thermal convection in a cylindrical cell. Phys. Fluids 9 , 1287–1295 (2010).

Wondrak, T., Pal, J., Stefani, F., Galindo, V. & Eckert, S. Visualization of the global flow structure in a modified Rayleigh-Bénard setup using contactless inductive flow tomography. Flow Meas. Instrum. 62 , 269–280 (2018).

Wondrak, T. et al. Three-dimensional flow structures in turbulent Rayleigh-Bénard convection at low Prandtl number Pr = 0.03. J. Fluid Mech. 974 , A48 (2023).

Article   MathSciNet   Google Scholar  

Cioni, S., Chaumat, S. & Sommeria, J. Effect of a vertical magnetic field on turbulent Rayleigh-Bénard convection. Phys. Rev. E 62 , R4520–R4523 (2000).

Aurnou, J. M. & Olsen, P. M. Experiments on Rayleigh-Bénard convection, magnetoconvection and rotating magnetoconvection in liquid gallium. J. Fluid Mech. 430 , 283–307 (2001).

Burr, U. & Müller, U. Rayleigh-Bénard convection in liquid metal layers under the influence of a vertical magnetic field. Phys. Fluids 13 , 3247–3257 (2001).

Zürner, T., Schindler, F., Vogt, T., Eckert, S. & Schumacher, J. Flow regimes of Rayleigh-Bénard convection in a vertical magnetic field. J. Fluid Mech. 894 , A21 (2020).

Vogt, T., Yang, J.-C., Schindler, F. & Eckert, S. Free-fall velocities and heat transport enhancement in liquid metal magneto-convection. J. Fluid Mech. 915 , A68 (2021).

Zürner, T. Refined mean field model of heat and momentum transfer in magnetoconvection. Phys. Fluids 32 , 107101 (2020).

Grannan, A. M. et al. Experimental pub crawl from Rayleigh-Bénard to magnetostrophic convection. J. Fluid Mech. 939 , R1 (2022).

Schumacher, J. The various facets of liquid metal convection. J. Fluid Mech. 946 , F1 (2022).

Xu, Y., Horn, S. & Aurnou, J. M. Thermoelectric precession in turbulent magnetoconvection. J. Fluid Mech. 930 , A8 (2020).

Horn, S. & Aurnou, J. The Elbert range of magnetostrophic convection. I. Linear theory. Proc. R. Soc. A 478 , 20220313 (2022).

Alfvén, H. Existence of electromagnetic-hydrodynamic waves. Nature 150 , 405–406 (1942).

Lundquist, S. Experimental demonstration of magneto-hydrodynamic waves. Nature 164 , 145–146 (1949).

Lehnert, B. Magneto-hydrodynamic waves in liquid sodium. Phys. Rev. 94 , 815–824 (1954).

Jameson, A. A demonstration of Alfvén waves part 1. Generation of standing waves. J. Fluid Mech. 19 , 513–527 (1964).

Iwai, K., Shinya, K., Takashi, K. & Moreau, R. Pressure change accompanying Alfvén waves in a liquid metal. Magnetohydrodynamics 39 , 245–249 (2003).

Alboussière, T. et al. Experimental evidence of Alfvén wave propagation in a gallium alloy. Phys. Fluids 23 , 096601 (2011).

Zaqarashvili, T. V. & Roberts, B. Two-wave interaction in ideal magnetohydrodynamics. Astron. Astrophys. 452 , 1053–1058 (2006).

Tomczyk, S. et al. Alfvén waves in the solar corona. Science 317 , 1192–1196 (2007).

Srivastava, A. K. et al. High-frequency torsional Alfvén waves as an energy source for coronal heating. Sci. Rep. 7 , 43147 (2017).

Gundrum, T. et al. Alfvén wave experiments with liquid rubidium in a pulsed magnetic field. Magnetohydrodynamics 58 , 389–396 (2022).

Velikhov, E. P. Stability of an ideally conducting liquid flowing between cylinders rotating in a magnetic field. Sov. Phys. JETP 36 , 995–998 (1959).

ADS   MathSciNet   Google Scholar  

Balbus, S. A. & Hawley, J. F. A powerful local shear instability in weakly magnetized disks. 1. Linear analysis. Astrophys. J. 376 , 214–221 (1991).

Ji, H. & Balbus, S. Angular momentum transport in astrophysics and in the lab. Phys. Today 66 , 27–33 (2013).

Rüdiger, G. & Schultz, M. The gap-size influence on the excitation of magnetorotational instability in cylindric Taylor-Couette flows. J. Plasma Phys. 90 , 905900105 (2024).

Ji, H., Burin, M., Schartman, E. & Goodman, J. Hydrodynamic turbulence cannot transport angular momentum effectively in astrophysical disks. Nature 444 , 343–346 (2006).

Nornberg, M. D., Ji, H., Schartman, E., Roach, A. & Goodman, J. Observation of magnetocoriolis waves in a liquid metal Taylor-Couette experiment. Phys. Rev. Lett. 104 , 074501 (2010).

Wang, Y., Gilson, E. P., Ebrahimi, F., Goodman, J. & Ji, H. Observation of axisymmetric standard magnetorotational instability in the laboratory. Phys. Rev. Lett. 129 , 115001 (2022).

Wang, Y. et al. Identification of a non-axisymmetric mode in laboratory experiments searching for standard magnetorotational instability. Nat. Comm. 13 , 4679 (2022).

Kirillov, O. N. & Stefani, F. On the relation of standard and helical magnetorotational instability. Astrophys. J. 712 , 52–68 (2010).

Hollerbach, R. & Rüdiger, G. New type of magnetorotational instability in cylindrical Taylor-Couette flow. Phys. Rev. Lett. 95 , 124501 (2005).

Hollerbach, R., Teeluck, V. & Rüdiger, G. Nonaxisymmetric magnetorotational instabilities in cylindrical Taylor-Couette flow. Phys. Rev. Lett. 104 , 044502 (2010).

Kirillov, O. N., Stefani, F. & Fukumoto, Y. A unifying picture of helical and azimuthal magnetorotational instability, and the universal significance of the Liu limit. Astrophys. J. 756 , 83 (2012).

Stefani, F. et al. Experimental evidence for magnetorotational instability in a Taylor-Couette flow under the influence of a helical magnetic field. Phys. Rev. Lett. 97 , 184502 (2006).

Stefani, F. et al. Experiments on the magnetorotational instability in helical magnetic fields. New J. Phys. 9 , 295 (2007).

Stefani, F. et al. Helical magnetorotational instability in a Taylor-Couette flow with strongly reduced Ekman pumping. Phys. Rev. E 80 , 066303 (2009).

Seilmayer, M. et al. Experimental evidence for nonaxisymmetric magnetorotational instability in a rotating liquid metal exposed to an azimuthal magnetic field. Phys. Rev. Lett. 113 , 024505 (2014).

Stefani, F. et al. The DRESDYN project: liquid metal experiments on dynamo action and magnetorotational instability. Geophys. Astrophys. Fluid Dyn. 113 , 51–70 (2019).

Tayler, R. J. Adiabatic stability of stars containing magnetic fields. 1. Toroidal fields. Mon. Not. R. Astron. Soc. 161 , 365–380. (1973).

Seilmayer, M. et al. Experimental evidence for a transient Tayler instability in a cylindrical liquid-metal column. Phys. Rev. Lett. 108 , 244501 (2012).

Mishra, A., Mamatsashvili, G. & Stefani, F. From helical to standard magnetorotational instability: predictions for upcoming liquid sodium experiments. Phys. Rev. Fluids 7 , 064802 (2022).

Mishra, A., Mamatsashvili, G. & Stefani, G. Nonlinear evolution of magnetorotational instability in a magnetized Taylor–Couette flow: scaling properties and relation to upcoming DRESDYN-MRI experiment. Phys. Rev. Fluids 8 , 083902 (2023).

Mishra, A., Mamatsashvili, G. & Stefani, G. Nonaxisymmetric modes of magnetorotational and possible hydrodynamical instabilities in the upcoming DRESDYN-MRI experiments: linear and nonlinear dynamics. Phys. Rev. Fluids 9 , 033904 (2024).

Mamatsashvili, G., Stefani, F., Hollerbach, R. & Rüdiger, G. Two types of axisymmetric helical magnetorotational instability in rotating flows with positive shear. Phys. Rev. Fluids 4 , 103905 (2019).

Vernet, M., Pereira, M., Fauve, S. & Gissinger, C. Turbulence in electromagnetically driven Keplerian flows. J. Fluid Mech. 924 , A29 (2021).

Vernet, M., Fauve, S. & Gissinger, C. Angular momentum transport by Keplerian turbulence in liquid metals. Phys. Rev. Lett. 129 , 074501 (2022).

He, X., Funfschilling, D., Nobach, H., Bodenschatz, E. & Ahlers, G. Transition to the ultimate state of turbulent Rayleigh-Bénard convection. Phys. Rev. Lett. 108 , 024502 (2012).

Huisman, S. G., van Gils, D. P. M., Grossmann, S. & Lohse, D. Ultimate turbulent Taylor-Couette flow. Phys. Rev. Lett. 108 , 024501 (2012).

Busse, F. H. The twins of turbulence research. Physics 5 , 4 (2012).

Stelzer, Z. et al. Experimental and numerical study of electrically driven magnetohydrodynamic flow in a modified cylindrical annulus. I. Base flow. Phys. Fluids 27 , 077101 (2015).

Stelzer, Z. et al. Experimental and numerical study of electrically driven magnetohydrodynamic flow in a modified cylindrical annulus. II. Instabilities. Phys. Fluids 27 , 084108 (2015).

Baylis, J. A. & Hunt, J. C. R. MHD flow in an annular channel; theory and experiment. J. Fluid Mech. 48 , 423–428 (1971).

Moresco, P. & Alboussière, T. Experimental study of the instability of the Hartmann layer. J. Fluid Mech. 504 , 167–181 (2004).

Boisson, J., Klochko, A., Daviaud, F., Padilla, V. & Aumaître, S. Travelling waves in a cylindrical magnetohydrodynamically forced flow. Phys. Fluids 24 , 044101 (2012).

Boisson, J., Monchaux, R. & Aumaître, S. Inertial regimes in a curved electromagnetically forced flow. J. Fluid Mech. 813 , 860–881 (2012).

Khalzov, I. V., Smolyakov, A. I. & Ilgisonis, V. I. Equilibrium magnetohydrodynamic flows of liquid metals in magnetorotational instability experiments. J. Fluid Mech. 644 , 257–280 (2010).

Poyé, A. et al. Scaling laws in axisymmetric magnetohydrodynamic duct flows. Phys. Rev. Fluids 5 , 043701 (2020).

Hollerbach, R., Wei, X., Noir, J. & Jackson, A. Electromagnetically driven zonal flows in a rapidly rotating spherical shell. J. Fluid Mech. 725 , 428–445 (2013).

Jackson, A. & Noir, J. Sodium experiments. ETH Zürich https://epm.ethz.ch/mfece/research/experiments/sodium-experiments.html (2024).

Shew, W. L., Sisan, D. R. & Lathrop, D. P. Mechanically forced and thermally driven flows in liquid sodium. Magnetohydrodynamics 38 , 121–127 (2001).

Lathrop, D. P., Shew, W. L. & Sisan, D. R. Laboratory experiments on the transition to MHD dynamos. Plasma Phys. Contr. Fusion 43 , A151 (2001).

Sisan, D. R. et al. Experimental observation and characterization of the magnetorotational instability. Phys. Rev. Lett. 93 , 114502 (2004).

Lathrop, D. P. & Forest, C. B. Magnetic dynamos in the lab. Phys. Today 64 , 40–45 (2011).

Zimmermann, D. S. et al. Characterization of the magnetorotational instability from a turbulent background state. AIP Conf. Proc. 733 , 13–20 (2004).

Gissinger, C., Ji, H. & Goodman, J. Instabilities in magnetized spherical Couette flow. Phys. Rev. E 84 , 026308 (2011).

Cardin, P., Brito, D., Jault, D., Nataf, H.-C. & Masson, J.-P. Towards a rapidly rotating liquid sodium dynamo experiment. Magnetohydrodynamics 38 , 177–189 (2002).

Nataf, H.-C. et al. Experimental study of super-rotation in a magnetostrophic spherical Couette flow. Geophys. Astrophys. Dyn. 100 , 281–298 (2006).

Dormy, E., Cardin, P. & Jault, D. MHD flow in a slightly differentially rotating spherical shell, with conducting inner core, in a dipolar magnetic field. Earth Planet. Sci. Lett. 160 , 15–30 (1998).

Schmitt, D. et al. Magneto-Coriolis waves in a spherical Couette flow experiment. Eur. J. Mech. B/Fluids 37 , 10–22 (2013).

Tigrine, Z., Nataf, H.-C., Schaeffer, N., Cardin, P. & Plunian, F. Torsional Alfvén waves in a dipolar magnetic field: experiments and simulations. Geophys. J. Int. 219 , S83–S100 (2019).

Gillet, N., Jault, D., Canet, E. & Fournier, A. Fast torsional waves and strong magnetic field within the Earth’s core. Nature 465 , 74–77 (2010).

Kasprzyk, C., Kaplan, E., Seilmayer, M. & Stefani, F. Transitions in a magnetized quasi-laminar spherical Couette flow. Magnetohydrodynamics 53 , 393–402 (2017).

Ogbonna, J., Garcia, F., Gundrum, T. H., Seilmayer, M. & Stefani, F. Experimental investigation of the return flow instability in magnetized spherical Couette flows. Phys. Fluids 32 , 124119 (2020).

Hollerbach, R. Non-axisymmetric instabilities in magnetic spherical Couette flow. Proc. Math. Phys. Eng. Sci. 465 , 2003–2013 (2009).

MathSciNet   Google Scholar  

Travnikov, V., Eckert, K. & Odenbach, S. Influence of an axial magnetic field on the stability of spherical Couette flows with different gap widths. Acta Mech. 219 , 255–268 (2011).

Garcia, F., Seilmayer, M., Giesecke, A. & Stefani, F. Modulated rotating waves in the magnetised spherical Couette system. J. Nonl. Sci. 29 , 2735–2759 (2019).

Garcia, F., Seilmayer, M., Giesecke, A. & Stefani, F. Four-frequency solution in a magnetohydrodynamic Couette flow as a consequence of azimuthal symmetry breaking. Phys. Rev. Lett. 125 , 264501 (2020).

Steenbeck, M. et al. Der experimentelle Nachweis einer elektromotorischen Kraft längs eines äußeren Magnetfeldes, induziert durch eine Strömung flüssigen Metalls (α-effekt). Mber. Dtsch. Akad. Wiss. Berl. 9 , 714–719 (1967).

Gans, R. F. On hydromagnetic precession in a cylinder. J. Fluid Mech. 45 , 111–130 (1970).

Lowes, F. J. & Wilkinson, I. Geomagnetic dynamo — a laboratory model. Nature 198 , 1158–1160 (1963).

Lowes, F. J. & Wilkinson, I. Geomagnetic dynamo — an improved laboratory model. Nature 219 , 717–718 (1968).

Wilkinson, I. The contribution of laboratory dynamo experiments to our understanding of the mechanism of generation of planetary magnetic fields. Geophys. Surv. 7 , 107–122 (1984).

Alboussière, T., Plunian, F. & Moulin, M. Fury: an experimental dynamo with anisotropic electrical conductivity. Proc. R. Soc. A 478 , 20220374 (2022).

Avalos-Zuñiga, R. & Priede, J. Realization of Bullard’s disk dynamo. Proc. R. Soc. A 479 , 20220740 (2023).

Krause, F. & Rädler, K.-H. Mean-Field Magnetohydrodynamics and Dynamo Theory (Akademie, 1980).

Alboussière, T., Drif, K. & Plunian, F. Dynamo action in sliding plates of anisotropic electrical conductivity. Phys. Rev. E 101 , 033108 (2020).

Plunian, F. & Alboussière, T. Axisymmetric dynamo action is possible with anisotropic conductivity. Phys. Rev. Res. 2 , 013321 (2020).

Plunian, F. & Alboussière, T. Axisymmetric dynamo action produced by differential rotation, with anisotropic electrical conductivity and anisotropic magnetic permeability. J. Plasma Phys. 97 , 905870110 (2021).

Priede, J. & Avalos-Zũniga, R. Feasible homopolar dynamo with sliding liquid-metal contacts. Phys. Lett. A 377 , 2093–2096 (2013).

Priede, J. & Avalos-Zũniga, R. Optimizing disc dynamo. Magnetohydrodynamics 59 , 65–72 (2023).

Bullard, E. C. The stability of a homopolar disc dynamo. Proc. Camb. Phil. Soc. 51 , 744–760 (1955).

Siemens, C. W. On the conversion of dynamical into electrical force without the aid of permanent magnetism. Proc. R. Soc. Lond. 15 , 367–369 (1867).

Wheatstone, C. On the augmentation of the power of a magnet by the reaction thereon of currents induced by the magnet itself. Proc. R. Soc. Lond. 15 , 369–372 (1867).

Larmor, J. How could a rotating body such as the Sun become a magnet? Rep. Brit. Assoc. Adv. Sci . https://doi.org/10.4159/harvard.9780674366688.c20 (1919).

Olson, P. Experimental dynamos and the dynamics of planetary cores. Annu. Rev. Earth Pl. Sc. 41 , 153–181 (2013).

Ponomarenko, Y. B. On the theory of hydromagnetic dynamos. Zh. Prikl. Mekh. Tekh. Fiz. ( USSR ) 6 , 47–51 (1973).

Gailitis, A. & Freibergs, Y. A. Theory of a helical MHD dynamo. Magnetohydrodynamics 12 , 127–129 (1976).

Gailitis, A. & Freibergs, Y. A. Nonuniform model of a helical dynamo. Magnetohydrodynamics 16 , 116–121 (1980).

Gailitis, A. et al. Experiment with a liquid-metal model of an MHD dynamo. Magnetohydrodynamics 23 , 349–353 (1987).

Gailitis, A. Design of a liquid sodium MHD dynamo experiment. Magnetohydrodynamics 32 , 68–62 (1996).

Stefani, F., Gerbeth, G. & Gailitis, A. in Transfer Phenomena in Magnetohydrodynamic and Electroconducting Flows (eds Alemany, A. et al.) 31–44 (Springer, 1999).

Gailitis, A. et al. Detection of a flow induced magnetic field eigenmode in the Riga dynamo facility. Phys. Rev. Lett. 84 , 4365–4368 (2000).

Gailitis, A. et al. Magnetic field saturation in the Riga dynamo experiment. Phys. Rev. Lett. 86 , 3024–3027 (2001).

Gailitis, A., Lielausis, O., Platacis, E., Gerbeth, G. & Stefani, F. The Riga dynamo experiment. Surv. Geophys. 24 , 247–267 (2003).

Gailitis, A., Lielausis, O., Platacis, E., Gerbeth, G. & Stefani, F. Riga dynamo experiment and its theoretical background. Phys. Plasmas 11 , 2838–2843 (2004).

Gailitis, A. & Lipsbergs, G. 2016 year experiments at Riga dynamo facility. Magnetohydrodynamics 53 , 349–356 (2017).

Lipsbergs, G. & Gailitis, A. 2022 year experiments at the Riga dynamo facility. Magnetohydrodynamics 58 , 417–424 (2022).

Gailitis, A. et al. Self-excitation in a helical liquid metal flow: the Riga dynamo experiments. J. Plasma Phys. 84 , 73584030 (2018).

Gailitis, A. Self-excitation conditions for a laboratory model of a geomagnetic dynamo. Magnetohydrodynamics 3 , 23–29 (1967).

Busse, F. H. A model of the geodynamo. Geophys. J. R. Astr. Soc. 42 , 437–459 (1975).

Roberts, G. O. Dynamo action of fluid motions with two-dimensional periodicity. Philos. Trans. R. Soc. Lond. A271 , 411–454 (1972).

Rädler, K.-H., Rheinhardt, M., Apstein, E. & Fuchs, H. On the mean-field theory of the Karlsruhe dynamo experiment. Nonlin. Proc. Geophys. 9 , 171–187 (2002).

Müller, U. & Stieglitz, R. The Karlsruhe dynamo experiment. Nonl. Proc. Geophys. 9 , 165–170 (2002).

Müller, U. & Stieglitz, R. A two-scale hydromagnetic dynamo experiment. J. Fluid Mech. 498 , 31–71 (2004).

Müller, U. & Stieglitz, R. Experiments at a two-scale dynamo test facility. J. Fluid Mech. 552 , 419–440 (2006).

Müller, U. & Stieglitz, R. The response of a two-scale kinematic dynamo to periodic flow forcing. Phys. Fluids 21 , 034108 (2009).

Tilgner, A. Predictions on the behaviour of the Karlsruhe dynamo. Acta Astron. Geophys. Univ. Comen. 19 , 51–62 (1997).

Tilgner, A. Numerical simulation of the onset of dynamo action in an experimental two-scale dynamo. Phys. Fluids 14 , 4092–4094 (2002).

Christensen, U. R. & Tilgner, A. Power requirement of the geodynamo from ohmic losses in numerical numerical and laboratory dynamos. Nature 429 , 169–171 (2004).

Avalos-Zuñiga, R., Xu, M., Stefani, F., Gerbeth, G. & Plunian, F. Cylindrical anisotropic α 2 dynamo. Geophys. Astrophys. Fluid Dyn. 101 , 389–404 (2007).

Dudley, M. L. & James, R. W. Time-dependent kinematic dynamos with stationary flows. Proc. R. Soc. A 425 , 407–429 (1989).

Xu, M., Stefani, F. & Gerbeth, G. The integral equation approach to kinematic dynamo theory and its application to dynamo experiments in cylindrical geometry. J. Comp. Phys. 227 , 8130–8144 (2008).

Monchaux, R. et al. Generation of a magnetic field by dynamo action in a turbulent flow of liquid sodium. Phys. Rev. Lett. 98 , 044502 (2007).

Berhanu, M. et al. Magnetic field reversals in an experimental turbulent dynamo. Europhys. Lett. 77 , 59001 (2007).

Ravelet, F. et al. Chaotic dynamos generated by a turbulent flow of liquid sodium. Phys. Rev. Lett. 101 , 074502 (2008).

Monchaux, R. et al. The von Kármán sodium experiment: turbulent dynamical dynamos. Phys. Fluids 21 , 035108 (2009).

Gallet, B. et al. Experimental observation of spatially localized dynamo magnetic fields. Phys. Rev. Lett. 108 , 144501 (2012).

Miralles, S. et al. Dynamo efficiency controlled by hydrodynamic bistability. Phys. Rev. E 89 , 063023 (2014).

Pétrélis, F., Fauve, S., Dormy, E. & Valet, J.-P. Simple mechanism for reversals of Earth’s magnetic field. Phys. Rev. Lett. 102 , 144503 (2009).

Pétrélis, F. & Fauve, S. Mechanism for magnetic field reversals. Phil. Trans. R. Soc. A 368 , 1595–1605 (2010).

Stefani, F., Gerbeth, G., Günther, U. & Xu, M. Why dynamos are prone to reversals. Earth Planet. Sci. Lett. 243 , 828–840 (2006).

Ravelet, F., Chiffaudel, A., Daviaud, F. & Léorat, J. Toward an experimental von Kármán dynamo: numerical studies for an optimized design. Phys. Fluids 17 , 117104 (2005).

Stefani, F. et al. Ambivalent effects of added layers on steady kinematic dynamos in cylindrical geometry: application to the VKS experiment. Eur. J. Mech. B/Fluids 25 , 894–908 (2006).

Verhille, G. et al. Induction in a von Kármán flow driven by ferromagnetic impellers. New J. Phys. 12 , 033006 (2010).

Giesecke, A., Stefani, F. & Gerbeth, G. Role of soft-iron impellers on the mode selection in the von-Kármán-sodium dynamo experiment. Phys. Rev. Lett. 104 , 044503 (2010).

Giesecke, A., Stefani, F. & Gerbeth, G. Influence of high-permeability discs in an axisymmetric model of the Cadarache dynamo experiment. New J. Phys. 14 , 053005 (2012).

Nore, C., Léorat, J., Guermond, J.-L. & Giesecke, A. Mean-field model of the von Kármán sodium dynamo experiment using soft iron impellers. Phys. Rev. E 91 , 013008 (2015).

Kreuzahler, S., Ponty, Y., Plihon, N., Homann, H. & Grauer, R. Dynamo enhancement and mode selection triggered by high magnetic permeability. Phys. Rev. Lett. 119 , 234501 (2017).

Miralles, S. et al. Dynamo threshold detection in the von Kármán sodium experiment. Phys. Rev. E 88 , 013002 (2013).

Forest, C. B. et al. Hydrodynamic and numerical modeling of a spherical homogeneous dynamo experiment. Magnetohydrodynamics 38 , 107–120 (2002).

Spence, E. J. et al. Observation of a turbulence-induced large scale magnetic field. Phys. Rev. Lett. 96 , 055002 (2006).

Nornberg, M. D. et al. Intermittent magnetic field excitation by a turbulent flow of liquid sodium. Phys. Rev. Lett. 97 , 044503 (2006).

Nornberg, M. D., Spence, E. J., Kendrick, R. D., Jacobson, C. M. & Forest, C. B. Measurements of the magnetic field induced by a turbulent flow of liquid metal. Phys. Plasmas 13 , 055901 (2006).

Spence, E. J. et al. Turbulent diamagnetism in flowing liquid sodium. Phys. Rev. Lett. 98 , 164503 (2007).

Rahbarnia, K. et al. Direct observation of the turbulent emf and transport of magnetic field in a liquid sodium experiment. Astrophys. J. 759 , 80 (2012).

Nornberg, M. D., Clark, M. M., Forest, C. B. & Plihon, N. Soft-iron impellers in the Madison sodium dynamo experiment. APS Div. Plasma Phys. Meet. Abstr. 2014 , CM10.005 (2014).

Zimmerman, D. S., Triana, S. A. & Lathrop, D. P. Bi-stability in turbulent, rotating spherical Couette flow. Phys. Fluids 23 , 065104 (2011).

Rieutord, M., Triana, S. A., Zimmerman, D. S. & Lathrop, D. P. Excitation of inertial modes in an experimental spherical Couette flow. Phys. Rev. E 86 , 026304 (2012).

Triana, S. A., Zimmerman, D. S. & Lathrop, D. P. Precessional states in a laboratory model of the Earth’s core. J. Geophys. Res. 117 , B04103 (2012).

Adams, M. M., Stone, D. R., Zimmerman, D. S. & Lathrop, D. P. Liquid sodium models of the Earth’s core. Prog. Earth Planet. Sci. 2 , 29 (2015).

Jaross, E., Wang, S., Perevalov, A. B., Rojas, R. E. & Lathrop, D. P. Progress on three meter spherical Couette experiment and implementation of TEM method. Bull. A. Phys. Soc . X27.00003 (2023).

Rojas, R. E., Perevalov, A., Zürner, T. & Lathrop, D. P. Experimental study of rough spherical Couette flows: increasing helicity toward a dynamo state. Phys. Rev. Fluids 6 , 033801 (2021).

Frick, P. et al. Non-stationary screw flow in a toroidal channel: way to a laboratory dynamo experiment. Magnetohydrodynamics 38 , 143–161 (2002).

Denisov, S. A., Noskov, V. I., Stepanov, R. A. & Frick, P. G. Measurements of turbulent magnetic diffusivity in a liquid-gallium flow. JTP Lett. 88 , 167–171 (2008).

Frick, P. et al. Direct measurement of effective magnetic diffusivity in turbulent flow of liquid sodium. Phys. Rev. Lett. 105 , 184502 (2010).

Colgate, S. A. et al. The New Mexico α  −  ω dynamo experiment: modelling astrophysical dynamos. Magnetohydrodynamics 38 , 129–142 (2002).

Colgate, S. A. et al. High magnetic shear gain in a liquid sodium stable Couette flow experiment: a prelude to an α  − Ω dynamo. Phys. Rev. Lett. 106 , 175003 (2011).

Si, J. et al. Suppression of turbulent resistivity in turbulent Couette flow. Phys. Plasmas 22 , 072304 (2015).

Seilmayer, M., Ogbonna, J. & Stefani, F. Convection-caused symmetry breaking of azimuthal magnetorotational instability in a liquid metal Taylor–Couette flow. Magnetohydrodynamics 56 , 225–236 (2020).

Mishra, A., Mamatsashvili, G., Galindo, V. & Stefani, F. Convective, absolute and global azimuthal magnetorotational instabilities. J. Fluid Mech. 922 , R4 (2021).

Horn, S. & Aurnou, J. Tornado-like vortices in the quasi-cyclostrophic regime of Coriolis-centrifugal convection. J. Turbul. 22 , 1–28 (2021).

Grants, I., Zhang, C., Eckert, S. & Gerbeth, G. Experimental observation of swirl accumulation in a magnetically driven flow. J. Fluid Mech. 616 , 135–152 (2008).

Vogt, T., Grants, I., Eckert, S. & Gerbeth, G. Spin-up of a magnetically driven tornado-like vortex. J. Fluid Mech. 736 , 641–662 (2013).

Jüstel, P. et al. Synchronizing the helicity of Rayleigh-Bénard convection by a tide-like electromagnetic forcing. Phys. Fluids 34 , 104115 (2022).

Stefani, F., Giesecke, A., Weber, N. & Weier, T. Synchronized helicity oscillations: a link between planetary tides and the solar cycle? Sol. Phys. 291 , 2197–2212 (2016).

Stefani, F., Giesecke, A. & Weier, T. A model of a tidally synchronized solar dynamo. Sol. Phys. 294 , 60 (2019).

Stefani, F., Stepanov, R. & Weier, T. Shaken and stirred: when Bond meets Suess-de Vries and Gnevyshev-Ohl. Sol. Phys. 296 , 88 (2021).

Klevs, M., Stefani, F. & Jouve, L. A synchronized two-dimensional α  − Ω model of the solar dynamo. Sol. Phys. 298 , 90 (2023).

Stefani, F., Horstmann, G. M., Klevs, M., Mamatsashvili, G. & Weier, T. Rieger, Schwabe, Suess-de Vries: the sunny beats of resonance. Sol. Phys. 299 , 51 (2024).

Léorat, J., Rigaud, F., Vitry, R. & Herpe, G. Dissipation in a flow driven by precession and application to the design of a MHD wind tunnel. Magnetohydrodynamics 39 , 321–326 (2003).

Léorat, J. Large scales features of a flow driven by precession. Magnetohydrodynamics 42 , 143–151 (2006).

Mouhali, W., Lehner, T., Léorat, J. & Vitry, R. Evidence for a cyclonic regime in a precessing cylindrical container. Exp. Fluids 53 , 1693–1700 (2012).

Tilgner, A. Precession driven dynamos. Phys. Fluids 17 , 034104 (2005).

Stefani, F. et al. DRESDYN — a new facility for MHD experiments with liquid sodium. Magnetohydrodynamics 48 , 103–114 (2012).

Giesecke, A., Vogt, T., Gundrum, T. & Stefani, F. Nonlinear large scale flow in a precessing cylinder and its ability to drive dynamo action. Phys. Rev. Lett. 120 , 024502 (2018).

Giesecke, A., Vogt, T., Gundrum, T. & Stefani, F. Kinematic dynamo action of a precession-driven flow based on the results of water experiments and hydrodynamic simulations. Geophys. Astrophys. Fluid Dyn. 113 , 235–255 (2019).

Pizzi, F., Giesecke, A., Simkanin, J. & Stefani, F. Prograde and retrograde precession of a fluid-filled cylinder. New J. Phys. 23 , 123016 (2021).

Kumar, V. et al. The effect of nutation angle on the flow inside a precessing cylinder and its dynamo action. Phys. Fluids 35 , 014114 (2023).

Aujogue, K., Pothérat, A., Bates, I., Debray, F. & Sreenivasan, B. Little Earth Experiment: an instrument to model planetary cores. Rev. Sci. Instr. 87 , 084502 (2016).

Tzeferacos, P. et al. Laboratory evidence of dynamo amplification of magnetic fields in a turbulent plasma. Nat. Commun. 9 , 591 (2018).

Bott, A. F. A. et al. Inefficient magnetic-field amplification in supersonic laser-plasma turbulence. Phys. Rev. Lett. 127 , 175002 (2021).

Forest, C. B. The Wisconsin plasma astrophysics laboratory. J. Plasma Phys. 81 , 345810501 (2015).

Weisberg, D. B. et al. Driving large magnetic Reynolds number flow in highly ionized, unmagnetized plasmas. Phys. Plasmas 24 , 056502 (2017).

Collins, C. et al. Stirring unmagnetized plasma. Phys. Rev. Lett. 108 , 115001 (2012).

Valenzuela-Villaseca, V. et al. Characterization of quasi-Keplerian, differentially rotating, free-boundary laboratory plasmas. Phys. Rev. Lett. 130 , 195101 (2023).

Guseva, A., Hollerbach, R., Willis, A. P. & Avila, M. Dynamo action in a quasi-Keplerian Taylor-Couette flow. Phys. Rev. Lett. 119 , 164501 (2017).

Petitdemange, L., Marcotte, F. & Gissinger, C. Spin-down by dynamo action in simulated radiative stellar layers. Science 379 , 300–303 (2023).

Yamada, M., Kulsrud, R. & Ji, H. Magnetic reconnection. Rev. Mod. Phys. 82 , 603–663 (2010).

Pontin, D. I. & Priest, E. R. Magnetic reconnection: MHD theory and modelling. Living Rev. Sol. Phys. 19 , 1 (2022).

Horstmann, G. M., Mamatsashvili, G., Giesecke, A., Zaqarashvili, T. & Stefani, F. Tidally forced planetary waves in the tachocline of solar-like stars. Astrophys. J. 944 , 48 (2023).

Hoff, M., Harlander, U. & Egbers, C. Experimental survey of linear and nonlinear inertial waves and wave instabilities in a spherical shell. J. Fluid Mech. 789 , 589–616 (2016).

Günther, U., Stefani, F. & Znojil, M. MHD α 2 -dynamo, Squire equation and PT-symmetric interpolation between square well and harmonic oscillator. J. Math. Phys. 46 , 063504 (2005).

Monteiro, G., Guerrero, G., Del Sordo, F., Bonanno, A. & Smolarkiewicz, P. K. Global simulations of Tayler instability in stellar interiors: a long-time multistage evolution of the magnetic field. Mon. Not. R. Astron. Soc. 521 , 1415–1428 (2023).

Weber, N., Galindo, V., Stefani, F. & Weier, T. The Tayler instability at low magnetic Prandtl numbers: between chiral symmetry breaking and helicity oscillations. New J. Phys. 17 , 113013 (2015).

Mamatsashvili, G. & Stefani, F. Linking dissipation-induced instabilities with nonmodal growth: the case of helical magnetorotational instability. Phys. Rev. E 94 , 051203 (2017).

Rincon, F. & Rieutord, M. The Sun’s supergranulation. Living Rev. Sol. Phys. 15 , 6 (2018).

Charbonneau, P. Dynamo models of the solar cycle. Living Rev. Sol. Phys. 17 , 4 (2020).

Goodman, J. & Ji, H. Magnetorotational instability of dissipative Couette flow. J. Fluid Mech. 462 , 365–382 (2002).

Download references

Acknowledgements

Funding from the European Research Council (ERC) under the Horizon 2020 research and innovation programme of the European Union (grant agreement number 787544) is gratefully acknowledged. The author is deeply indebted to A. Gailitis (Riga) for his leadership in the joint work on the Riga dynamo experiment, as well as to G. Rüdiger (Potsdam) and R. Hollerbach (Leeds) for the long-term collaboration on the magnetorotational and Tayler instability. Cordial thanks go to the current and former students and colleagues of the author at Helmholtz-Zentrum Dresden-Rossendorf, in particular to T. Albrecht, R. Avalos-Zuñiga, C. Kasprzyk, S. Eckert, M. Fischer, J. Forbriger, V. Galindo, F. Garcia, G. Gerbeth, A. Giesecke, T. Gundrum, U. Günther, J. Herault, G. Horstmann, P. Jüstel, E. Kaplan, M. Klevs, N. Krauter, O. Kirillov, V. Kumar, K. Liu, G. Mamatsashvili, A. Mishra, J. Ogbonna, M. Ratajczak, S. Röhrborn, J. Szklarski, M. Seilmayer, J. Šimkanin, T. Vogt, T. Weier, N. Weber, T. Wondrak and M. Xu, for all their help in solving a wide variety of problems in basic and applied magnetohydrodynamics. G. Gerbeth is also thanked for the constructive comments on the draft.

Author information

Authors and affiliations.

Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany

Frank Stefani

You can also search for this author in PubMed   Google Scholar

Corresponding author

Correspondence to Frank Stefani .

Ethics declarations

Competing interests.

The author declares no competing interests.

Peer review

Peer review information.

Nature Reviews Physics thanks Cary Forest, Nicolas Plihon and Santiago Triana for their contribution to the peer review of this work.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Rights and permissions

Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.

Reprints and permissions

About this article

Cite this article.

Stefani, F. Liquid-metal experiments on geophysical and astrophysical phenomena. Nat Rev Phys (2024). https://doi.org/10.1038/s42254-024-00724-1

Download citation

Accepted : 02 May 2024

Published : 10 June 2024

DOI : https://doi.org/10.1038/s42254-024-00724-1

Share this article

Anyone you share the following link with will be able to read this content:

Sorry, a shareable link is not currently available for this article.

Provided by the Springer Nature SharedIt content-sharing initiative

Quick links

• Explore articles by subject
• Guide to authors
• Editorial policies

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Information

• Author Services

Initiatives

You are accessing a machine-readable page. In order to be human-readable, please install an RSS reader.

All articles published by MDPI are made immediately available worldwide under an open access license. No special permission is required to reuse all or part of the article published by MDPI, including figures and tables. For articles published under an open access Creative Common CC BY license, any part of the article may be reused without permission provided that the original article is clearly cited. For more information, please refer to https://www.mdpi.com/openaccess .

Feature papers represent the most advanced research with significant potential for high impact in the field. A Feature Paper should be a substantial original Article that involves several techniques or approaches, provides an outlook for future research directions and describes possible research applications.

Feature papers are submitted upon individual invitation or recommendation by the scientific editors and must receive positive feedback from the reviewers.

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

Original Submission Date Received: .

• Active Journals
• Find a Journal
• Proceedings Series
• For Authors
• For Reviewers
• For Editors
• For Librarians
• For Publishers
• For Societies
• For Conference Organizers
• Open Access Policy
• Institutional Open Access Program
• Special Issues Guidelines
• Editorial Process
• Research and Publication Ethics
• Article Processing Charges
• Testimonials
• Preprints.org
• SciProfiles
• Encyclopedia

Article Menu

• Subscribe SciFeed
• Recommended Articles
• Author Biographies
• Google Scholar
• on Google Scholar
• Table of Contents

Find support for a specific problem in the support section of our website.

Please let us know what you think of our products and services.

Visit our dedicated information section to learn more about MDPI.

JSmol Viewer

Geophysical assessment of structurally controlled mineral resources at wadi el-nakheel, eastern desert, egypt.

1. Introduction

2. materials and methods, 2.1. location and geology, 2.2. methodology, 2.2.1. geomagnetic data processing, 2.2.2. magnetic modeling, 3. results and discussion, 4. conclusions, author contributions, data availability statement, acknowledgments, conflicts of interest.

• AbdelAal, G.Z.; El-Haddad, A.E.; Badri, M.S.; Mohamed, M.A. Inferring Depth to basement using Airborne magnetic data at Wadi El Nakheel area, Eastern desert of Egypt. Assiut Univ. J. Multdisiciplinary Sci. Res. 2019 , 48 , 1–11. [ Google Scholar ]
• Yousif, M.; Sracek, O. Integration of geological investigations with multi-GIS data layers for water resources assessment in arid regions: El Ambagi Basin, Eastern Desert, Egypt. Environ. Earth Sci. 2016 , 75 , 684. [ Google Scholar ] [ CrossRef ]
• Mansour, S.; Hasebe, N.; Khedr, M.Z.; Tamura, A.; Shehata, A.A. Tectonic-Thermal Evolution of the Wadi El-Dahal Area, North Eastern Desert, Egypt: Constraints on the Suez Rift Development. Minerals 2023 , 13 , 1021. [ Google Scholar ] [ CrossRef ]
• Shallaly, N.A. Metamorphic evolution of Pan-African Wadi El Miyah Metasediments, Central Eastern Desert, Egypt: A distinctive LP/HT metapelitic sequence from the northern Arabian–Nubian Shield. Arab. J. Geosci. 2019 , 12 , 54. [ Google Scholar ] [ CrossRef ]
• Ahmadi, H.; Pekkan, E. Fault-Based Geological Lineaments Extraction Using Remote Sensing and GIS—A Review. Geosciences 2021 , 11 , 183. [ Google Scholar ] [ CrossRef ]
• Arnous, M.O.; ElMowafy, A.A.; Azzaz, S.A.; Omar, A.E.; Abdel Hafeez, W.M. Exploration radioactive mineralization using mappable data integration approach: Example from Wadi Dahab area, Southeastern Sinai, Egypt. Arab. J. Geosci. 2021 , 14 , 599. [ Google Scholar ] [ CrossRef ]
• Cianfarra, P.; Salvini, F. Lineament Domain of Regional Strike-Slip Corridor: Insight from the Neogene Transtensional De Geer Transform Fault in NW Spitsbergen. Pure Appl. Geophys. 2015 , 172 , 1185–1201. [ Google Scholar ] [ CrossRef ]
• Dong, L.J.; Pei, Z.W.; Xie, X.; Zhang, Y.H.; Yan, X.H. Early identification of abnormal regions in rock-mass using traveltime tomography. Engineering 2023 , 22 , 191–200. [ Google Scholar ] [ CrossRef ]
• Zhang, Y.B.; Yao, X.L.; Liang, P.; Wang, K.X.; Sun, L.; Tian, B.Z.; Liu, X.X.; Wang, S.Y. Fracture evolution and localization effect of damage in rock based on wave velocity imaging technology. J. Cent. South Univ. 2021 , 28 , 2752–2769. [ Google Scholar ] [ CrossRef ]
• Seif, E.S.S.A. Evaluation of geotechnical properties of Cretaceous sandstone, Western Desert, Egypt. Arab. J. Geosci. 2016 , 9 , 299. [ Google Scholar ] [ CrossRef ]
• Araffa, S.A.S.; Rabeh, T.T.T.; Mousa, S.E.D.A.W.; Nabi, S.H.A.; Al Deep, M. Integrated geophysical investigation for mapping of manganese-iron deposits at Wadi Al Sahu area, Sinai, Egypt—A case study. Arab. J. Geosci. 2020 , 13 , 823. [ Google Scholar ] [ CrossRef ]
• Mekkawi, M.M.; ElEmam, A.E.; Taha, A.I.; Al Deep, M.A.; Araffa, S.A.S.; Massoud, U.S.; Abbas, A.M. Integrated geophysical approach in exploration of iron ore deposits in the North-eastern Aswan-Egypt: A case study. Arab. J. Geosci. 2021 , 14 , 721. [ Google Scholar ] [ CrossRef ]
• Saleh, A.; Abdelmoneim, M.; Abdelrady, M.; Al Deep, M. Subsurface structural features of the basement complex and mineralization zone investigation in the Barramiya area, Eastern Desert of Egypt, using magnetic and gravity data analysis. Arab. J. Geosci. 2018 , 11 , 676. [ Google Scholar ] [ CrossRef ]
• Mousa, S.A.; Abdel Nabi, S.H.; Sultan, S.A.; Mansour, S.A.; Al-Deep, M.A. Geophysical exploration of titanomagnetite ore deposits by geomagnetic and geoelectric methods. SN Appl. Sci. 2020 , 2 , 444. [ Google Scholar ] [ CrossRef ]
• Bakheit, A.A.; Abdel Aal, G.Z.; El-Haddad, A.E.; Ibrahim, M.A. Subsurface tectonic pattern and basement topography as interpreted from aeromagnetic data to the south of El-Dakhla Oasis, western desert, Egypt. Arab. J. Geosci. 2014 , 7 , 2165–2178. [ Google Scholar ] [ CrossRef ]
• Abdelrady, M.; Elhadek, H.; Abdelmoneim, M.; Saleh, A. Orogenic lode-gold deposits and listvenization processes in the El-Barramiya area, Eastern Desert, Egypt. Environ. Earth Sci. 2023 , 82 , 420. [ Google Scholar ] [ CrossRef ]
• Alkholy, A.; Saleh, A.; Ghazala, H.; Al Deep, M.; Mekkawi, M. Groundwater exploration using drainage pattern and geophysical data: A case study from Wadi Qena, Egypt. Arab. J. Geosci. 2023 , 16 , 92. [ Google Scholar ] [ CrossRef ]
• Ji, N.; Qin, X.; Wu, H.; Wang, Z.; Du, W.; Liu, Y.; Zhang, T.; Zhang, S.; Shi, Q. Occurrence Characteristics of Lead–Zinc Mine and Low-Flying Aeromagnetic Prospecting in a Forested Region of Yichun City. Minerals 2023 , 13 , 1414. [ Google Scholar ] [ CrossRef ]
• Zhdanov, M.S.; Wan, L.; Jorgensen, M. Joint Three-Dimensional Inversion of Gravity and Magnetic Data Collected in the Area of Victoria Mine, Nevada, Using the Gramian Constraints. Minerals 2024 , 14 , 292. [ Google Scholar ] [ CrossRef ]
• Poliakovska, K.; Annesley, I.R.; Hajnal, Z. Geophysical Constraints to the Geological Evolution and Genesis of Rare Earth Element–Thorium–Uranium Mineralization in Pegmatites at Alces Lake, SK, Canada. Minerals 2024 , 14 , 25. [ Google Scholar ] [ CrossRef ]
• CONOCO. Geological Map of Egypt, Scale 1:500,000, NG-36-NE ; Quseir Datasheet; The Egyptian General Petroleum Corporation: Cairo, Egypt, 1987. [ Google Scholar ]
• El Bahariya, G.A. Ghadir Ophiolites, Eastern Desert, Egypt: A Complete Sequence of Oceanic Crust in the Arabian-Nubian Shield. In The Geology of the Arabian-Nubian Shield. Regional Geology Reviews ; Hamimi, Z., Fowler, A.R., Liégeois, J.P., Collins, A., Abdelsalam, M.G., Abd EI-Wahed, M., Eds.; Springer: Cham, Switzerland, 2021. [ Google Scholar ] [ CrossRef ]
• Trueblood, P.M. Explanatory Text for a Geologic Map of an Area North of Quseir, Egypt. Master’s Thesis, Bryn Mawr College, Wales, UK, 1981; 72p. [ Google Scholar ]
• Zaghloul, E.A. Geology of Dakhla Oasis, Western Desert, Egypt. In Sustainable Water Solutions in the Western Desert, Egypt: Dakhla Oasis ; Iwasaki, E., Negm, A.M., Elbeih, S.F., Eds.; Earth and Environmental Sciences Library, Springer: Cham, Switzerland, 2021. [ Google Scholar ] [ CrossRef ]
• El Ayyat, A.M. Lithostratigraphy, sedimentology, and cyclicity of the Duwi Formation (late Cretaceous) at Abu Tartur plateau, Western Desert of Egypt: Evidences for reworking and redeposition. Arab. J. Geosci. 2015 , 8 , 99–124. [ Google Scholar ] [ CrossRef ]
• Gay, S. Fundamental characteristics of aeromagnetic lineaments, their geological significance, and their significance to geology. In The New Basement Tectonics ; American Stereo Map Company: Salt Lake, UT, USA, 1972. [ Google Scholar ]
• Talwani, M.; Worzel, J.I.; Landisman, M. Rapid gravity computations for two dimensional bodies with application to the Mendtcino submarine fracture Lone. J. Geophys. Res. 1959 , 64 , 49–59. [ Google Scholar ] [ CrossRef ]
• AerService, D. Aeromagnetic Anomaly Map of the Eastern Desert, Egypt ; scale 1: 50,000, compiled by the Egyptian General Petroleum Corporation; Aero Service Division; Western Geophysical Company of America: Houston, TX, USA, 1983; Volume 6. [ Google Scholar ]
• Roest, W.R.; Pilkington, M. Identifying remnant magnetization effect in magnetic data. Geophysics 1993 , 58 , 653–659. [ Google Scholar ] [ CrossRef ]
• Nabighian, M.N. The analytic signal of two-dimensional magnetic bodies with polygonal cross-section; its properties and use for automated interpretation. Geophysics 1972 , 37 , 507–517. [ Google Scholar ] [ CrossRef ]
• Nabighian, M.N. Towards a three dimensional automatic interpretation of potential field data via generalized Hilbert transform: Fundamental relations. Geophysics 1984 , 47 , 780–786. [ Google Scholar ] [ CrossRef ]
• Muszala, S.P.; Grindlay, N.R.; Bird, R.T. Three-dimensional Euler deconvolution and tectonic interpretation of marine magnetic anomaly data in the Puerto Rico trench. J. Geophys. Res. 1999 , 104 , 29175–29188. [ Google Scholar ] [ CrossRef ]
• Nabighian, M.N.; Hansen, R.O. Unification of Euler and Werner deconvolution in three dimensions via the generalized Hilbert transform. Geophysics 2001 , 66 , 1805–1810. [ Google Scholar ] [ CrossRef ]
• Thompson, D.T. EULDPH—A New technique for making computer-assisted depth estimates from magnetic data. Geophysics 1982 , 47 , 31–37. [ Google Scholar ] [ CrossRef ]
• Geosoft Oasis Montaj ; Mapping and Application System Inc.: Toronto, ON, Canada, 2015.

Click here to enlarge figure

Share and Cite

Al Deep, M.; Ibrahim, A.S.; Saleh, A. Geophysical Assessment of Structurally Controlled Mineral Resources at Wadi El-Nakheel, Eastern Desert, Egypt. Resources 2024 , 13 , 83. https://doi.org/10.3390/resources13060083

Al Deep M, Ibrahim AS, Saleh A. Geophysical Assessment of Structurally Controlled Mineral Resources at Wadi El-Nakheel, Eastern Desert, Egypt. Resources . 2024; 13(6):83. https://doi.org/10.3390/resources13060083

Al Deep, Mohamed, Arwa Sameer Ibrahim, and Ahmed Saleh. 2024. "Geophysical Assessment of Structurally Controlled Mineral Resources at Wadi El-Nakheel, Eastern Desert, Egypt" Resources 13, no. 6: 83. https://doi.org/10.3390/resources13060083

Article Metrics

Article access statistics, further information, mdpi initiatives, follow mdpi.

Subscribe to receive issue release notifications and newsletters from MDPI journals

• SUGGESTED TOPICS
• The Magazine
• Newsletters
• Managing Yourself
• Managing Teams
• Work-life Balance
• The Big Idea
• Data & Visuals
• Reading Lists
• Case Selections
• HBR Learning
• Topic Feeds
• Account Settings
• Email Preferences

How to Make a “Good” Presentation “Great”

• Guy Kawasaki

Remember: Less is more.

A strong presentation is so much more than information pasted onto a series of slides with fancy backgrounds. Whether you’re pitching an idea, reporting market research, or sharing something else, a great presentation can give you a competitive advantage, and be a powerful tool when aiming to persuade, educate, or inspire others. Here are some unique elements that make a presentation stand out.

• Fonts: Sans Serif fonts such as Helvetica or Arial are preferred for their clean lines, which make them easy to digest at various sizes and distances. Limit the number of font styles to two: one for headings and another for body text, to avoid visual confusion or distractions.
• Colors: Colors can evoke emotions and highlight critical points, but their overuse can lead to a cluttered and confusing presentation. A limited palette of two to three main colors, complemented by a simple background, can help you draw attention to key elements without overwhelming the audience.
• Pictures: Pictures can communicate complex ideas quickly and memorably but choosing the right images is key. Images or pictures should be big (perhaps 20-25% of the page), bold, and have a clear purpose that complements the slide’s text.
• Layout: Don’t overcrowd your slides with too much information. When in doubt, adhere to the principle of simplicity, and aim for a clean and uncluttered layout with plenty of white space around text and images. Think phrases and bullets, not sentences.

As an intern or early career professional, chances are that you’ll be tasked with making or giving a presentation in the near future. Whether you’re pitching an idea, reporting market research, or sharing something else, a great presentation can give you a competitive advantage, and be a powerful tool when aiming to persuade, educate, or inspire others.

• Guy Kawasaki is the chief evangelist at Canva and was the former chief evangelist at Apple. Guy is the author of 16 books including Think Remarkable : 9 Paths to Transform Your Life and Make a Difference.

Partner Center