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1. What is Geology?
Geology is a study of earth science, which involves structure, composition and evolution of earth formation. The word geology means 'Study of the Earth'. Also known as geoscience or earth science, Geology is the primary Earth science and looks at how the earth formed, its structure and composition, and the types of processes acting on it. Geology is the scientific study of the Earth, including its materials, processes, and history. It involves examining rocks, minerals, and fossils to understand how the Earth has changed over time. Geologists study processes like volcanic eruptions, earthquakes, and erosion, and they use this knowledge to explore natural resources, assess environmental impacts, and understand past climates. Essentially, geology helps us understand the Earth's structure and the forces that have shaped its surface and interior over billions of years.
2. What is Geophysics?
Geophysics is a exploration deals with identification of sub-surface formation such as sand, clay and types of rock mineral ore body such as iron, gold, copper by using geophysical exploration techniques which may be electrical, seismic, magnetic and gravity with the aid of suitable geophysical serving equipment. Geophysics is the study of the Earth using physical principles and methods to understand its structure and processes.
Example: If you’re investigating where to drill for oil, you might use seismic surveys—a geophysical technique. By sending shock waves into the ground and measuring how they bounce back, you can create a picture of what’s below the Earth's surface. This helps geophysicists identify potential oil reserves and decide the best drilling locations.
3. What is the relationship between Geology & Geophysics?
Geology and geophysics are closely related fields that often complement each other in studying the Earth. Here’s how they intersect:
1. Shared Goals: Both geology and geophysics aim to understand the Earth's structure, processes, and history. Geology focuses on the materials and processes that shape the Earth's surface and interior, while geophysics applies physical principles to investigate these aspects.
2. Complementary Methods: Geology relies on fieldwork, rock samples, and fossil analysis to study Earth's materials and historical changes. Geophysics uses physical measurements and techniques (like seismic waves, magnetic fields, and gravity) to gather data about the Earth's interior. Geophysical data can help geologists interpret subsurface conditions that are difficult to access directly.
3. Integrated Studies: Geologists often use geophysical data to enhance their understanding of geological formations. For example, seismic surveys (a geophysical method) can reveal the structure of rock layers, which geologists can then analyze to understand their composition and history.
4. Resource Exploration: Both fields are crucial in exploring natural resources. Geophysics can locate potential mineral or oil deposits, while geology helps in understanding and evaluating these resources' quality and potential.
In summary, while geology and geophysics have different focuses and methods, they are interdependent. Geophysics provides tools and data that inform geological interpretations, and geology offers the context that helps make sense of geophysical observations.
4. What is the use of Geophysical equipment?
Geophysical equipment is used to investigate and measure various physical properties of the Earth's subsurface. This equipment helps geophysicists gather data that can be used for exploration, environmental monitoring, and understanding geological processes. Here’s a look at some common types of geophysical equipment and their uses:
1. Seismometers:
• Use: Measure seismic waves generated by earthquakes or artificial sources.
• Example: Seismometers are used to monitor and analyze earthquake activity, helping to determine the location, depth, and magnitude of seismic events.
2. Magnetometers:
• Use: Measure variations in the Earth’s magnetic field.
• Example: Magnetometers are employed in mineral exploration to detect magnetic anomalies that might indicate the presence of ore deposits.
3. Gravimeters:
• Use: Measure variations in the Earth's gravitational field.
• Example: Gravimeters help in oil and gas exploration by identifying gravity anomalies that may suggest the presence of subsurface structures like salt domes.
4. Ground-Penetrating Radar (GPR):
• Use: Use radar pulses to image the subsurface.
• Example: GPR is used in archaeology to locate buried artifacts or in construction to detect underground utilities and voids before excavation.
5. Electrical Resistivity Tomography (ERT):
• Use: Measure the resistance of the ground to electrical current.
• Example: ERT is used to identify contamination in groundwater by detecting changes in soil resistivity caused by pollutants.
6. Gravity Meters:
• Use: Measure small changes in gravity that can indicate the presence of different geological features.
• Example: Used in mineral exploration to locate ore bodies or in geological mapping to study the Earth's structure.
7. Magneto telluric (MT):
• Use: Measure variations in the Earth's electrical conductivity.
• Example: MT is used to study the Earth's crust and mantle and is useful in locating geothermal resources.
These geophysical tools provide essential data that help in resource exploration, environmental monitoring, and understanding the Earth's internal processes. They are crucial in a range of applications from natural resource management to civil engineering and environmental protection.
5. What is the Geo-electrical resistivity method?
The geo-electrical resistivity method, or electrical resistivity tomography (ERT), is a geophysical technique used to measure the electrical resistance of the Earth's subsurface. By injecting electrical current into the ground and measuring the resulting voltage, this method helps to create images of subsurface resistivity variations, which can reveal geological structures and resource locations.
How it Works
1. Electrode Placement: Electrodes are placed on the ground in a specific array (e.g., a straight line or grid).
2. Current Injection: An electrical current is passed through two electrodes (the current electrodes).
3. Voltage Measurement: The voltage drop is measured between two other electrodes (the potential electrodes).
4. Resistivity Calculation: The resistance of the subsurface is calculated from the voltage and current measurements.
Basic Formula
The fundamental relationship in the resistivity method is given by Ohm’s Law and the geometry of the electrode array. The resistivity (ρ) of the subsurface can be calculated using the following formula
ρ=AR*K
where:
• P = Electrical resistivity of the subsurface (ohm-meters, Ω⋅ m)
• R = Measured resistance (ohms, Ω)
• K = Geometric factor (dimensionless, depending on electrode configuration)
• A = Area of the electrode array (m², depending on configuration)
Geometric Factor (K)
The geometric factor K depends on the electrode configuration and spacing. For a simple array, such as the Wenner or Schlumberger array, K is defined by the geometry of the electrode setup. For example, in the Wenner array:
K=π*a
where a is the distance between the current electrodes (or potential electrodes) in the Wenner array configuration.
Applications
1. Environmental Studies: Detecting contamination by identifying variations in resistivity caused by pollutants.
2. Engineering: Assessing soil and rock properties for construction, such as finding water tables or unstable zones.
3. Archaeology: Mapping buried structures or artifacts by detecting resistivity contrasts with surrounding soil.
4. Resource Exploration: Locating groundwater or mineral deposits by mapping resistivity variations.
The geo-electrical resistivity method is valued for its ability to provide detailed, non-invasive images of the subsurface, making it useful for various geological, environmental, and engineering applications.
6. What is the advantage of 2-D ERT over 1-D VES method?
The 2-D Electrical Resistivity Tomography (ERT) method offers several advantages over the 1-D Vertical Electrical Sounding (VES) method, primarily in terms of the level of detail and the spatial resolution of subsurface imaging. Here’s a comparative overview:
1-D VES Method
Description:
The 1-D Vertical Electrical Sounding (VES) method involves measuring resistivity at different depths by varying the distance between the current and potential electrodes in a single vertical profile. The resistivity is measured as a function of depth, providing a vertical profile of resistivity but no lateral information.
Formula:
For the VES method, the resistivity (ρ) is derived from the resistance (R) using: ρ=R⋅K where K is a geometric factor that depends on the electrode configuration and spacing.
2-D ERT Method
Description:
The 2-D Electrical Resistivity Tomography (ERT) method involves measuring resistivity along a line with a series of electrodes arranged in a linear array. It provides a two-dimensional image of subsurface resistivity variations along the line, capturing both vertical and horizontal variations in resistivity.
Advantages of 2-D ERT Over 1-D VES:
1. Spatial Resolution:
• 2-D ERT: Provides detailed lateral and vertical information, producing a two-dimensional cross-sectional image of the subsurface. This helps in identifying lateral changes in resistivity, such as geological boundaries or anomalies.
• 1-D VES: Only provides vertical profiles of resistivity, missing out on lateral variations.
2. Geological Interpretation:
• 2-D ERT: Offers a more comprehensive view of subsurface structures, allowing for better geological interpretation of features like faults, layers, and voids. It can reveal structures that extend horizontally and provide a clearer picture of geological contexts.
• 1-D VES: Limited to depth profiling, which can be less effective for understanding complex geological features that have significant lateral extent.
3. Survey Efficiency:
• 2-D ERT: Can cover more ground quickly and provide more data in a single survey, which is useful for large-scale investigations or detailed site assessments.
• 1-D VES: Requires multiple soundings at different locations to cover a larger area, making it less efficient for extensive surveys.
4. Data Interpretation:
• 2-D ERT: The resulting images are typically easier to interpret for identifying subsurface features and anomalies due to the visual representation of resistivity variations.
• 1-D VES: Interpretation relies on correlating multiple vertical profiles, which can be more complex and less intuitive.
Formula for 2-D ERT
The general formula for resistivity in 2-D ERT is: ρ=R*K/A
7. What is the purpose of 3-D ERT? What way 3-D method is better than 1-D VES & 2-D ERT?
The purpose of 3-D Electrical Resistivity Tomography (ERT) is to provide a detailed, three-dimensional image of subsurface resistivity variations. This method is used for a range of applications where understanding the full spatial distribution of subsurface features is crucial. Here’s how 3-D ERT compares to 1-D Vertical Electrical Sounding (VES) and 2-D ERT, with examples illustrating its advantages:
Purpose of 3-D ERT
1. Comprehensive Subsurface Imaging:
Purpose: To visualize and model the resistivity distribution of the subsurface in three dimensions, allowing for a complete understanding of spatial relationships and geological structures.
2. Detailed Characterization:
Purpose: To detect and map complex features such as faults, ore bodies, groundwater plumes, and archaeological remains with high resolution in both horizontal and vertical dimensions.
3. Complex Site Assessments:
Purpose: To investigate areas with intricate subsurface conditions where lateral and vertical variations are significant and need to be accurately characterized.
Advantages of 3-D ERT Over 1-D VES and 2-D ERT
1. Spatial Resolution:
• 3-D ERT: Provides detailed imaging in all three dimensions, offering a comprehensive view of subsurface features. This helps in accurately mapping complex structures and identifying features that extend horizontally and vertically.
• 1-D VES: Offers resistivity measurements at discrete points, providing only vertical profiles without lateral context. This limits the ability to understand the spatial extent of features.
• 2-D ERT: Provides a cross-sectional view along a line but lacks information about features outside this line, missing out on lateral variations and the full spatial context.
Example: In groundwater studies, 3-D ERT can map the extent of a contaminated plume in three dimensions, showing how it spreads both horizontally and vertically. In contrast, 1-D VES would only reveal the vertical profile at specific points, and 2-D ERT would show a cross-sectional slice, potentially missing important lateral variations.
2. Detailed Subsurface Models:
• 3-D ERT: Allows for the creation of detailed and accurate 3D models of subsurface resistivity, which is useful for understanding complex geological formations and making informed decisions.
• 1-D VES: Limited to depth profiling, making it challenging to interpret complex or heterogeneous subsurface conditions accurately.
• 2-D ERT: While providing a better view than 1-D VES, it only captures a single horizontal slice of the subsurface, which can be insufficient for understanding the full 3D context.
Example: In mining exploration, 3-D ERT can accurately model the shape and extent of ore bodies, including their vertical depth and horizontal spread. 1-D VES would miss lateral extensions, while 2-D ERT would only provide a cross-sectional view, potentially missing important lateral variations.
3. Enhanced Accuracy and Interpretation:
• 3-D ERT: Reduces uncertainty by providing a full volumetric view of the subsurface, leading to more accurate identification and interpretation of subsurface features.
• 1-D VES: Interpretation is less clear and more challenging due to the lack of spatial context.
• 2-D ERT: Offers more information than 1-D VES but still lacks the comprehensive view provided by 3-D ERT.
Example: In archaeological surveys, 3-D ERT can reveal the layout of buried structures, such as walls and foundations, in three dimensions, providing a clear picture of their spatial arrangement. 1-D VES would not provide sufficient detail, and 2-D ERT would only show features along a single plane.
Summary
• 3-D ERT offers a detailed, three-dimensional view of subsurface resistivity variations, making it ideal for complex investigations requiring high spatial resolution and comprehensive data.
• 1-D VES provides limited vertical profiles, lacking spatial context.
• 2-D ERT offers cross-sectional data but does not capture the full three-dimensional nature of subsurface features.
Overall, 3-D ERT provides a more complete and accurate depiction of subsurface conditions compared to 1-D VES and 2-D ERT, making it invaluable for detailed site investigations and complex geological studies.
8. What is ‘IP’ method and What way it is useful for geophysical exploration?
The Induced Polarization (IP) method is a geophysical technique used to measure the electrical chargeability of subsurface materials. This method is particularly useful for exploring mineral deposits, groundwater, and environmental conditions due to its sensitivity to various subsurface features.
How the IP Method Works
1. Current Injection: An electrical current is applied to the ground using a pair of electrodes.
2. Voltage Measurement: After the current is turned off, the voltage response of the ground is measured over time using another pair of electrodes. This response indicates how long the ground retains the electrical charge.
3. Chargeability Calculation: Chargeability is a measure of how the subsurface material stores and releases electrical charge. It is calculated from the decay of the voltage after the current is switched off.
Formulas
1. Chargeability (M): Chargeability is typically calculated using the time-domain decay of voltage. The formula used is:
M=Vdecay/Von⋅1/T
where:
• Vdecay = Voltage measured during the decay period
• Von = Voltage during current injection
• T = Time constant or decay time
In practice, chargeability is often computed using an integration of the decay curve, which can be more complex but provides a more accurate measure of the chargeability.
2. Resistivity (ρ): Electrical resistivity is calculated using Ohm's Law:
ρ=R*K
where:
• R = Measured resistance (ohms, Ω)
• K = Geometric factor depending on the electrode configuration
Resistivity is typically measured alongside IP to provide complementary information.
Applications and Benefits of the IP Method
1. Mineral Exploration:
• Usefulness: IP is particularly effective for locating mineral deposits, especially those with sulfide minerals, which exhibit high chargeability. These minerals cause significant polarization effects that are detected by the method.
• Example: IP surveys are used to detect copper, gold, and lead deposits, which often show strong chargeability anomalies.
2. Groundwater Exploration:
• Usefulness: The method helps in identifying groundwater resources by detecting chargeability anomalies associated with water-saturated zones. This can reveal the presence of aquifers or water-bearing formations.
• Example: IP can locate groundwater plumes by identifying differences in chargeability between saturated and unsaturated zones.
3. Environmental and Engineering Applications:
• Usefulness: IP is used to detect and map contaminants, such as heavy metals or organic pollutants, and to assess subsurface conditions for construction projects.
• Example: In environmental surveys, IP can identify contamination plumes in groundwater or locate underground storage tanks.
4. Archaeological Investigations:
• Usefulness: The method helps in locating buried artifacts or structures by detecting variations in chargeability due to different materials or soil conditions.
• Example: IP surveys can reveal ancient walls, foundations, or other archaeological features by detecting resistivity contrasts.
Advantages of the IP Method
• Sensitivity to Mineralization: The IP method is sensitive to metallic minerals, particularly sulfides, making it valuable in mineral exploration.
• Enhanced Detection: Provides additional information on subsurface features beyond what resistivity alone can reveal.
• Non-Invasive: Offers a non-destructive way to investigate subsurface conditions, avoiding the need for drilling or excavation.
9.What is a seismograph?
A seismograph (or seismometer) is an instrument used to detect and record the vibrations or movements of the Earth caused by seismic waves from earthquakes, volcanic activity, or other ground-shaking events. It measures the ground's motion and records it as a seismogram, which is a graphical representation of the seismic waves.
How a Seismograph Works
1. Detection:
A seismograph consists of a mass (or pendulum) suspended on a spring or other support, which remains relatively stationary while the ground moves. The instrument has a base that is anchored to the ground and moves with it.
2. Recording:
As the ground shakes, the base of the seismograph moves, causing the relative motion between the mass and the base. This relative motion is detected by sensors and recorded.
3. Seismogram:
The relative motion between the mass and the base is recorded on a rotating drum or digital recorder. This creates a seismogram, which shows the amplitude and frequency of the seismic waves over time.
Basic Components of a Seismograph
• Mass (or Pendulum): The component that remains relatively stationary while the ground moves.
• Base: The part of the seismograph that moves with the ground.
• Spring or Support: Suspends the mass and allows it to remain stationary relative to the ground.
• Sensor: Measures the relative motion between the mass and the base.
• Recorder: Records the detected motion as a seismogram.
Seismograph Formula
The seismograph’s output can be analyzed using the following formula to relate the amplitude of the seismic waves to the distance from the earthquake source:
A=F/k
where:
• A = Amplitude of the seismic waves
• F = Force applied to the seismograph (related to the ground motion)
• k = Spring constant of the seismograph (or the stiffness of the support system)
Additionally, the seismograph’s response can be expressed in terms of frequency and damping:
x¨+2ζωn*x˙+ωn2*x=0
where:
• x¨ = Acceleration of the mass
• x˙ = Velocity of the mass
• x = Displacement of the mass
• ωn = Natural frequency of the seismograph
• ζ = Damping ratio
Applications of Seismographs
1. Earthquake Monitoring:
To detect and record seismic waves from earthquakes, helping to determine the earthquake's location, magnitude, and depth.
2. Volcanic Activity:
To monitor volcanic activity by detecting ground movements associated with eruptions or magma movement.
3. Building and Structural Monitoring:
To assess the impact of seismic events on structures and evaluate their stability.
4. Exploration Geophysics:
To explore subsurface structures and resources by analyzing seismic waves generated by artificial sources.
10. What is the functional difference between SRT ( seismic refraction test), MASW & bore hole seismic?
- Seismic Refraction Test (SRT): This method involves sending seismic waves into the subsurface and recording the reflected waves that bounce back from different geological layers. It’s commonly used in hydrocarbon exploration and geological mapping to detect subsurface structures, such as faults and stratigraphy.
- Multichannel Analysis of Surface Waves (MASW): MASW measures the velocity of surface waves to determine subsurface stiffness, typically used for shallow subsurface investigations. It is less sensitive to deeper layers compared to SRT but is advantageous for mapping soil profiles and determining shear wave velocity.
- Borehole Seismic: This technique involves placing geophones inside a borehole to record seismic waves generated at the surface or within the borehole. It provides high-resolution images of subsurface structures around the borehole and is often used in reservoir characterization and monitoring.
11. What is a Geophone?
A geophone is a device used to detect and measure ground motion, specifically seismic waves. It converts ground movement (velocity) into an electrical signal, which can then be recorded and analyzed. Geophones are commonly used in seismic surveys to detect subsurface structures by measuring the waves reflected back from geological layers. They are critical in both active and passive seismic methods.
12. What is Geophysical Borehole logging?
Geophysical borehole logging involves measuring the physical properties of rocks and fluids within a borehole. Various sensors are lowered into the borehole to record data such as resistivity, density, and acoustic properties. This information helps to characterize the subsurface environment, including identifying different rock types, fluid content, and the presence of minerals or hydrocarbons. It is widely used in hydrocarbon exploration, mining, and groundwater studies.
13. What is the purpose of gamma logging, SP logging & resistivity logging?
- Gamma Logging: This measures natural gamma radiation emitted by rocks, helping to identify different rock types, particularly in sedimentary formations. It’s often used in shale and clay content evaluation.
- Spontaneous Potential (SP) Logging: SP logging measures the natural electrical potentials that occur in the subsurface due to differences in ion concentrations. It’s mainly used to identify permeable zones and differentiate between various lithologies.
- Resistivity Logging: This method measures the electrical resistivity of subsurface formations. It’s useful for identifying the presence of hydrocarbons, water saturation, and the porosity of rocks. It helps in distinguishing between conductive (e.g., water-filled) and resistive (e.g., hydrocarbon-bearing) formations.
14. What is the purpose of caliper logging?
Caliper logging measures the diameter of a borehole as it is drilled. The primary purpose is to identify borehole irregularities, such as enlargements or constrictions, which may indicate zones of weak rock or fracture. This information is crucial for proper casing and cementing operations, as well as for interpreting other logging data by providing insights into borehole stability and conditions.
15. What is OTV & ATV ?
- Optical Televiewer (OTV): OTV is a borehole logging tool that captures high-resolution optical images of the borehole wall, allowing for detailed visualization of fractures, bedding planes, and other geological features.
- Acoustic Televiewer (ATV): ATV uses acoustic waves to create an image of the borehole wall. It is particularly useful in fluid-filled boreholes and provides information about the borehole’s geometry and fractures.
16. What is the advantage of ‘ATV’ or ‘OTV’?
The advantage of ATV and OTV lies in their ability to provide detailed images of the borehole wall, which helps in structural and lithological analysis. OTV is better suited for dry or transparent fluid-filled boreholes and offers high-resolution color images. ATV, on the other hand, works well in fluid-filled boreholes and provides valuable acoustic data in addition to images, which can be used to assess rock hardness and fracture orientation.
17. What is MT method or magneto telluric method ?
The Magneto telluric (MT) method is a geophysical technique that measures natural variations in the Earth’s electromagnetic field to determine the electrical resistivity of subsurface rocks. It is capable of imaging subsurface structures from depths of a few hundred meters to several kilometers. MT is widely used in mineral exploration, geothermal investigations, and deep groundwater studies due to its ability to detect resistivity contrasts in the subsurface.
18. Whether MT method is reliable for groundwater Aquifer mapping?
The MT method can be reliable for groundwater aquifer mapping, especially in identifying large-scale aquifer systems and deep-seated aquifers. It’s particularly effective in regions with significant resistivity contrasts between aquifers and surrounding formations. However, its resolution at shallow depths may be limited compared to other methods like VES (Vertical Electrical Sounding), so it’s often used in combination with other geophysical methods for more detailed aquifer characterization.
19. Which method is more accurate for hydrogeological investigation MT method or VES method?
Hydrogeological investigations, the choice between MT and VES methods depends on the depth and scale of the study area. The VES method is often preferred for shallow to moderate depths and provides detailed resistivity profiles that are highly effective for delineating groundwater aquifers. MT, on the other hand, is more suitable for deeper investigations and broader geological contexts. While MT offers greater depth penetration, VES is usually more accurate for detailed aquifer mapping in shallower subsurface layers.
20. What are the advantages and challenges of applying 2D and 3D resistivity imaging for subsurface investigations in different environmental and geological settings?
21. How is Ohm’s Law used to determine the resistivity of subsurface materials in electrical resistivity surveys(VES Soundings/ ERT) geophysical surveys?
Geophysical methods measure some physical (physics) property of materials within the earth (geo). The electrical method measures the resistivity of soils and rocks. The basic physical law used is Ohm’s Law. Ohm’s Law gives the relationship between the voltage (V), current (I) and resistance (R). It is given by
V = R I
This form of Ohm’s Law is for a current flow in an electrical circuit through a resistor.
22. How does the apparent resistivity (ρa)differ from the true resistivity (ρ) when the medium is non-homogeneous, and why is this relationship complex?
The apparent resistivity value ⍴a calculated by
⍴a = k ⧍V /I = k R
is only equal to the true resistivity for a homogeneous medium. The relationship between the apparent resistivity and the true resistivity is complex for a general non-homogeneous medium, as in all cases for measurements in the earth.
23. What are the Common arrays used in resistivity surveys and their geometric factors?
24. What is the field procedure for VES Soundings?
In a field survey, the resistivity of the subsurface is measured by passing a current through the ground. Four metal electrodes are planted into the ground. An electric current (10mA to 1 A) is injected into the ground using electrodes C1 and C2. The resulting voltage difference at two points on the ground surface is measured using two electrodes, P1 and P2 . Changes in the ground resistivity will cause deviations in the current flow and the resulting measured voltage difference.
25. Electrical properties of rocks and soils?
The resistivity of a soil or rock depends on the nature of the solid matrix, porosity and pore fluid. Except for conductive minerals (sulfides, graphite, clay, etc) the main effect is the pore fluid (usually water). As a rule, igneous/metamorphic rocks have the highest resistivity, followed by sedimentary rocks and soils.
26. Narrate briefly the evolution of Electrical Resistivity method starting from inception to till date?
1920s to 1980s : 1-D. Sounding and profiling surveys using 4 electrode resistivity meters.
1990s : 2-D. Major change with multi-electrode systems. Widespread use, more realistic images.
2000s : 3-D. Multi-channel meters. Dense areal data coverage. Mineral exploration with offset pole-dipole layouts. Able to resolve complex mineral systems.
2010s : 4-D. Environmental monitoring (landslides, aquifers, landfills). Remote systems with wireless control 1-D sounding surveys carry out measurements with different spacings between electrodes but with a common center. The data is usually plotted as a sounding curve.
Assume a simplified mathematical model for the subsurface that consist of horizontal layers.
Correlate model properties with known geology.
The interpretation of data from 1-D sounding surveys can be automatically done using an inversion program. The user enters the data (apparent resistivity values and electrode spacings), together with a starting model (number of layers with estimated thickness and resistivity). The program then automatically adjust the thickness and resistivity of the layers until the calculated apparent resistivity values are ‘close’ to the measured values.
27. Example of 1-D inversion?
The interpretation of data from 1-D sounding surveys can be automatically done using an inversion program. The user enters the data (apparent resistivity values and electrode spacings), together with a starting model (number of layers with estimated thickness and resistivity). The program then automatically adjust the thickness and resistivity of the layers until the calculated apparent resistivity values are ‘close’ to the measured values.
28. Limitations of 1-D surveys?
Traditional resistivity sounding surveys only give a 1-D picture of the subsurface, which is probably too simple in many cases.
1-D models are probably too inaccurate for most areas where there are significant lateral and vertical variations.
This method is still used for extremely deep aquifers and in many developing parts of the world where access to multi-electrode resistivity meter systems is limited.
29. 2-D electrical imaging surveys?
The 1990s saw a rapid growth in 2-D surveys driven by availability of multi-electrode instruments, fast PCs and automatic inversion software. A computer control program automatically selects the appropriate 4 electrodes for each measurement to give a 2-D coverage of the subsurface. A large variety of arrays and survey arrangements can be used with such a system.
30. Example for 2-D survey – Groundwater?
Since the mid-1990s it has become a ‘standard’ geophysical tool for small companies in the hydrological, environmental and engineering sectors. It has enabled the mapping of complex structures previously not possible with 1-D surveys. Together with seismic surveys, 2-D ERT surveys are now offered by most small geophysical survey companies particularly for groundwater related problems.
Below is an example of a survey to map fractures filled with groundwater in a hard-rock environment in the Blue Ridge Mountain area in eastern USA.
31. What are the example for 2-D Environmental?
Another area where 2-D surveys have become popular is mapping pollution from landfills, tailing ponds etc. The contaminants frequently have much lower resistivity than normal groundwater.
Below is an example of a survey to map a pollution plume that has migrated across the boundaries of a landfill.
32. What is a 2-D electrical imaging survey?
A 2-D imaging survey is usually carried out with a computer controlled resistivity meter system connected to a multi-electrode cable system. The control software automatically selects the appropriate four electrodes for each measurement to give a 2-D coverage of the subsurface. A large variety of arrays and survey arrangements can be used with such a system.
33. What is the 2-D surveys – typical multi-electrode systems?
Two of the most widely used ‘high-end’ systems are the Abem Terrameter LS 2 and Iris Syscal systems, WERI Series, WGMD-9 , GD-10 , GD-20 etc., Many system has a ‘center-spread’ arrangement using two cables with take-outs attached to the main resistivity meter placed at the center. The systems can have 24 to 256 electrodes, but 32 is probably the practical minimum. One common system is the Abem SAS and LS series that uses a time-domain I.P. measuring system. The Abem SAS4000 system is an example that uses a 4-cable system. In a 2-D survey, the cables are laid out along a straight line, and an internal computer automatically selects the electrodes for each measurement using a control file provided.
34. What is the Pseudo section data plotting method?
To plot the data from a 2-D imaging survey, the pseudo section contouring method is normally used. The horizontal location of the point is placed at the mid-point of the set of electrodes used to make that measurement. The vertical location of the plotting point is placed at the median depth of investigation of the array used. For example, the data point measured by electrodes 1, 2, 3 and 4 are plotted at the mid-point between electrodes 2 and 3 in the diagram below.
35. What are the example of a typical pseudo section?
The pseudo section plot normally shows smoothly changing contours, particularly when a ‘conventional’ array is used, such as the Wenner array in the example below. There is a large variation of about 100 times in the apparent resistivity values, but they change in a smooth manner across the section.
If there are sudden jumps in the apparent resistivity values, it is usually an indication of bad data.
36. How using the pseudo section to identify bad data points?
Bad data points fall into two broad categories, i.e. “systematic” and “random” noise. Systematic noise is usually caused by some sort of failure during the survey, and some of the apparent resistivity values are much higher or lower than other readings. Random noise include effects such telluric currents that affects all the readings, and the readings to be slightly lower or higher.
The pseudo section plot below two areas with unusually high values compared to neighboring points.
Methods to remove bad data points:
Before carrying out the inversion, you should first take a look at the data as a pseudo section plot or a profile plot. This option is possible for surveys carried out with one of the standard arrays, such as Wenner, Schlumberger, dipole-dipole, pole-dipole and gradient.
The bad data points with “systematic” noise show up as spots with unusually low or high values in the pseudo section, such as the example below. Note a few points with very high resistivity values which are bad data points. They are probably caused by equipment problems rather than random background noise.
Method to remove bad data points before inversion:
One method is to remove the bad data points manually, particular if there only a small number of bad data points, is to plot the data as profiles. The bad data points are usually much higher or lower than the other data points. The bad data points can be removed by clicking them with the mouse within the Res2dinvx64 program.
2-D forward modeling:
In the inversion of a data set, it is necessary to calculate the apparent resistivity values for the model used – this is the forward modeling problem. In forward modeling, the subsurface resistivity distribution is specified, and the purpose is to calculate the apparent resistivity that would be measured by a survey over such a structure. The 2-D subsurface is divided into many cells, and the finite-difference or finite-element method is used to calculate the apparent resistivity values.
37. What is inversion?
The purpose of an inversion program is to convert the apparent resistivity values into the true resistivity of the subsurface.
⍴a→ ⍴true
The relationship between the apparent resistivity and the true resistivity is a very complex relationship, depending on whether the subsurface model is 1-D, 2-D or 3-D. Converting the data into a model is the inversion step.
1-D inversion example
2-D inversion example
38. What is 2-D inversion?
After the field survey, the resistance measurements are usually changed to apparent resistivity values. The purpose of the inversion is to convert the apparent resistivity values into a model section. The conversion of the apparent resistivity data to a model for the subsurface resistivity is carried out on a microcomputer using an automatic inversion program.
39. What are the Basic Principle of Seismic Refraction Method?
Seismic Refraction Survey is one of the important tools in the family of exploration geophysics. Seismic investigations utilize the fact that elastic waves (also called seismic waves) travel with different velocities in different rocks. By generating seismic waves at a point and observing the time of arrival of these waves at several other points on the surface of the earth, it is possible to determine the velocity distribution and locate the subsurface interfaces where the waves are reflected or refracted. The underlying theory of seismic refraction survey is that whenever a seismic wave travels in the boundary separating two media, energy is partly reflected and partly refracted. Hence, by choosing the refracted arrivals alone, we can relate the delay in the arrival times of refracted seismic waves at different locations to a lateral or transverse variation in the velocity of different subsurface layers.
40. What is MASW Technique?
Multichannel Analysis of Surface Waves (MASW) is a non-destructive surface wave technique based fundamentally on the dispersion of Rayleigh wave, analysis of which helps in determination of the vertical distribution of the S-wave velocity underground The S-wave velocity is a function of the elastic properties of the subsurface medium and is directly related to the hardness and stiffness of the materials. Dispersion is the process by which, the mechanical properties of the subsurface layers with different frequencies/wavelength have different phase velocity in a vertically homogeneous medium, as the mechanical property remains unchanged, the wavelengths vary with depth while the phase velocity remains constant. Whereas, in case of vertical heterogeneity, the wavelength varies depth-wise, and the phase velocity is different for each subsurface stratum that has specific mechanical characteristics.
The MASW study procedure includes data acquisition as well as processing to evaluate Rayleigh wave dispersion characteristics and finally inversion of the dispersion curve to determine 1-D & 2-D distribution of S-wave velocity up to 30m depth.
How to Generate of 1-D and 2-D S-Wave Velocity Images?
As per the desired application, the results of MASW study are presented either in the form of 1-D or 2-D image for visualizing the detailed status of the subsurface and evaluating the site characteristics. The procedure for generating S-wave velocity distribution in 1-D form.
The procedure for generating 2-D S-wave velocity image involves collection of data in a roll-along manner with fixed source-receiver configuration . The processing & inversion being done in an automated manner. Basically, the 2-D image includes 1-D observations combined through interpolation process.
Applications of MASW:
* Furnishes high resolution 1-D & 2-D illustrations: Having the capacity to resolve gradual changes in vertical velocity distribution, helping thereby in deciphering thin layers.
* Delineates zones of weaknesses: Based on the variation in S-wave velocity distribution, it can detect anomalous zones viz., voids, sand lenses, shear zones, etc.
* Demarcates weathered zone: It clearly identifies the zone of weathering because of its high resolving power.
* Estimates depth-to-bedrock: Rocks and soils boundaries can be easily deciphered as per their specific shear strength properties.
* Determines variations in stiffness: It provides in-situ means of determining stiffness profile of soils & rocks and predicting ground deformations without the need of boreholes.
* Computes Weighted Average Shear Wave Velocity Vs(30): The Vs(30) is an important input for estimating site specific seismic design parameters and is useful in seismic microzonation study as well.
* Assesses Liquefaction Potential: The value of blow count ‘N’ (of SPT) can be indirectly determined using empirical relationships between ‘N’ and S-wave velocity.
41. What is GPR?
Ground-Penetrating Radar (GPR) is a geophysical method used to investigate the subsurface by sending high-frequency electromagnetic waves into the ground and analyzing the reflected signals.
Principle of Operation:
Emission and Reflection: GPR systems emit short pulses of electromagnetic waves into the ground using an antenna. These waves travel through the subsurface and are reflected back to the surface by different materials or interfaces with varying dielectric properties.
Signal Reception: The reflected waves are detected by the receiver antenna. The time it takes for the waves to return is used to estimate the depth of the reflecting layers.
Data Interpretation: The data collected is typically displayed as a radargram, a cross-sectional image of the subsurface, where reflections are interpreted to determine the location, size, and properties of subsurface features.
Applications of GPR:
Archaeology: GPR is used to locate, and map buried artifacts, structures, and archaeological features without excavation.
Engineering and Construction: In construction, GPR helps in assessing the condition of concrete structures, locating reinforcements, and identifying voids or delamination’s.
Geology and Hydrogeology: GPR is used to map geological structures, such as faults and layers, and to study groundwater and soil properties.
Environmental Studies: GPR helps in detecting and mapping contaminants, landfills, and other subsurface anomalies related to environmental issues.
Forensic Investigation: GPR is used in forensic investigations to locate buried evidence or graves.
Advantages of GPR:
Non-destructive: GPR provides a non-invasive method for subsurface exploration, allowing for real-time data collection.
High Resolution: It can provide high-resolution images of the subsurface, enabling detailed analysis.
Versatile: GPR can be used in various environments, including urban areas, rural locations, and underwater.
Depth Penetration: The depth of penetration is limited by the frequency of the radar waves. Higher frequencies provide better resolution but less penetration, while lower frequencies penetrate deeper but with lower resolution.
Material Properties: GPR performance is affected by the dielectric properties of subsurface materials. It is less effective in highly conductive materials like clay or saltwater.
Data Interpretation: Interpreting GPR data can be complex and may require specialized knowledge and experience.
Typical of GPR Equipment:
1. Antennas: Used to emit and receive electromagnetic waves. They come in various frequencies depending on the required resolution and depth of investigation.
2. Radar System: Includes the electronics to generate, transmit, and receive the radar pulses.
3. Data Acquisition System: Records the radar signals and converts them into a format for analysis, such as a radargram.
GPR is a powerful tool in geophysics and other fields for understanding the subsurface environment and making informed decisions based on subsurface conditions.
Well logging in geophysics is a method used to obtain detailed information about the geological formations encountered while drilling a well. It involves the measurement of physical and chemical properties of the subsurface materials to aid in the exploration, development, and production of natural resources such as oil, gas, and groundwater.
42. What is Well Logging?
Well logging in geophysics is a method used to obtain detailed information about the geological formations encountered while drilling a well. It involves the measurement of physical and chemical properties of the subsurface materials to aid in the exploration, development, and production of natural resources such as oil, gas, and groundwater.
Principle of Well Logging:
Measurement Tools: Instruments, often referred to as "logs," are lowered into the wellbore on a wireline or in some cases are integrated into the drill string.
Data Acquisition: These tools measure various physical properties of the rock and fluid in the wellbore as they descend through the formation.
Data Analysis: The collected data are recorded and analyzed to provide insights into the geological formations, fluid content, porosity, and other characteristics.
Types of Well Logging:
1. Electrical Logging
Logging Resistivity: Measures the electrical resistance of rock formations to determine the presence of hydrocarbons, water, or other fluids. Types include:
a. Spontaneous Potential (SP) Log : Measures the natural electrical potential generated by the formation.
b. Induction Log : Uses electromagnetic induction to measure resistivity.
c. Later log : Measures resistivity using electrodes placed at different depths.
2. Gamma Ray Logging
Gamma Ray Log : Measures natural gamma radiation from the formation to identify lithology and correlate rock types. It helps distinguish between clay-rich and sand-rich formations.
3. Density Logging
Bulk Density Log : Measures the density of the rock formation using gamma rays and other methods to estimate porosity and rock type.
4. Neutron Logging
Neutron Porosity Log : Measures the hydrogen content in the formation, which is used to estimate porosity. It is particularly useful in identifying oil and gas zones.
5. Sonic Logging
Sonic Log : Measures the speed of acoustic waves through the formation to estimate rock properties like porosity and elasticity. It is used to determine formation strength and acoustic impedance.
6. Nuclear Magnetic Resonance (NMR) Logging
NMR Log : Measures the magnetic properties of hydrogen nuclei in the formation to provide information on porosity, permeability, and fluid types.
a. Formation Pressure Testing
Pressure Transient Testing:
Measures the natural electrical potential generated by the formation.
b. Formation Testing
Sampling and Testing:
Uses electromagnetic induction to measure resistivity.
7. Caliper Logging
Caliper Log : Measures the diameter of the wellbore to identify irregularities and assess the wellbore stability.
8. Sidewall Coring and Logging
Sidewall Core Log : Involves taking core samples from the wellbore wall for detailed analysis of rock properties and formation characteristics.
Applications of Well Logging:
* Oil and Gas Exploration: Helps in identifying potential hydrocarbon reservoirs and assessing their viability.
* Groundwater Studies: Provides data on aquifer properties and groundwater quality.
* Geotechnical Engineering: Assesses soil and rock properties for construction and safety evaluations.
* Environmental Monitoring: Helps in understanding and managing contamination in subsurface environments.
Advantages of Well Logging:
* Detailed Information: Provides comprehensive data about subsurface formations.
* Real-time Data: Enables real-time monitoring and decision-making during drilling.
* Non-destructive: Allows for the assessment of formations without disturbing the well.
Limitations of Well Logging:
* Cost: Logging operations can be expensive, especially in deep or challenging environments.
* Interpretation Complexity: Data interpretation can be complex and requires specialized knowledge.
* Tool Limitations: Some logging tools may have limitations in certain formations or environments.
Well logging is a critical component in the exploration and production of natural resources, providing essential data for making informed decisions and optimizing resource extraction.
Certainly! Here are some geophysics-related questions specifically focused on well logging:
1. What is the primary purpose of well logging in geophysics?
The primary purpose of well logging in geophysics is to collect detailed information about subsurface rock formations and fluids by measuring various physical properties in a wellbore. This data helps in characterizing geological formations, identifying potential reservoirs, and optimizing resource extraction.
2. How does resistivity logging work, and what information can it provide about subsurface formations?
Resistivity logging measures the electrical resistance of subsurface rocks by passing an electrical current through them and measuring the resulting voltage. It provides information about the presence of hydrocarbons, water, and the general lithology of the formations. High resistivity often indicates the presence of hydrocarbons, while low resistivity suggests water or conductive minerals.
3. What are the differences between spontaneous potential (SP) logs and induction resistivity logs in well logging?
SP logs measure the natural electrical potential differences between the wellbore and the surrounding formation, primarily used for identifying lithological boundaries and salinity contrasts. Induction resistivity logs use electromagnetic induction to measure the formation resistivity and are particularly useful in conductive environments where direct current measurements are challenging.
4. How is gamma ray logging used to distinguish between different types of rock formations?
Gamma ray logging measures natural gamma radiation emitted by the formation. High gamma ray counts typically indicate clay-rich formations, while lower counts suggest sand or limestone. This logging helps in identifying lithology and correlating rock types across different wells.
5. What information can density logging provide, and how is it used in conjunction with other logging methods?
Density logging measures the bulk density of the rock formation, which is used to estimate porosity and differentiate between various rock types. It is often used in conjunction with other logs, such as neutron porosity logs, to cross-check porosity estimates and enhance the accuracy of subsurface models.
6. How does neutron porosity logging work, and what are its main applications?
Neutron porosity logging measures the hydrogen content in the formation by detecting the scattering of neutrons from a source. Since hydrocarbons and water contain hydrogen, this log helps estimate porosity and differentiate between water-bearing and hydrocarbon-bearing zones. It is often used in combination with density logs for more accurate porosity calculations.
7. What are some key considerations when interpreting well log data from highly heterogeneous or fractured reservoirs?
When interpreting well log data from heterogeneous or fractured reservoirs, key considerations include the impact of fractures on log readings, variations in resistivity and porosity due to heterogeneous rock types, and potential deviations caused by complex geological structures. Advanced modeling and integration with other data types (e.g., seismic) may be required for accurate interpretation.
8. How does sonic logging contribute to understanding rock properties, and what parameters does it measure?
Sonic logging measures the travel time of acoustic waves through the formation to determine rock properties such as porosity, elastic moduli, and formation strength. It provides data on the velocity of compressional and shear waves, which can be used to estimate formation porosity and mechanical properties.
9. What are the advantages and limitations of using nuclear magnetic resonance (NMR) logging in well logging?
NMR logging provides detailed information on pore size distribution, fluid types, and permeability by measuring the relaxation times of hydrogen nuclei. It offers advantages in distinguishing between different fluids and assessing formation permeability. However, it can be limited by its sensitivity to high salinity and the complexity of interpreting relaxation times in heterogeneous formations.
10. How is formation pressure testing conducted, and what information does it provide about a well?
Formation pressure testing involves measuring the pressure within the formation while the well is temporarily isolated. This data provides information on reservoir pressure, fluid types, and the presence of potential flow zones. It helps in understanding reservoir behavior and optimizing production strategies.
11. What factors influence the selection of well logging tools and techniques for a given geological setting?
Factors influencing the selection of well logging tools and techniques include the type of geological formations (e.g., clay, sand, limestone), the expected depth of investigation, the presence of conductive or radioactive materials, and the specific objectives of the logging (e.g., porosity measurement, fluid identification).
12. What are the common challenges in acquiring well log data in deepwater or high-pressure environments, and how can they be addressed?
Common challenges in deepwater or high-pressure environments include high temperatures, high pressures, and the potential for tool malfunction. These challenges can be addressed by using specialized logging equipment designed for extreme conditions, ensuring accurate calibration, and incorporating redundancy in data collection.
These questions cover various aspects of well logging, from operational principles and techniques to data interpretation and challenges, providing a comprehensive overview of the topic in geophysics.
43. What is Magneto Telluric?
Magneto Telluric (MT) is a geophysical method used to study the Earth's subsurface by measuring natural variations in the Earth's magnetic and electric fields. MT methods are particularly useful for exploring deep geological structures and are employed in various fields such as mineral exploration, hydrogeology, and geothermal energy.
Principle of Magneto Telluric (MT):
1. Natural Field Variations: MT methods utilize naturally occurring time-varying electromagnetic fields. These fields are generated by natural sources such as solar activity (solar winds) and lightning strikes, which induce electric currents in the Earth's crust.
2. Measurement: MT involves measuring the variations in the Earth's magnetic and electric fields at the surface. These variations occur over a range of frequencies from extremely low to high frequencies (e.g., from 0.001 Hz to several kHz).
3. Data Acquisition: Electric field measurements are typically made using electric dipole antennas, and magnetic field measurements are made using magnetometers. The ratio of the electric field to the magnetic field is used to infer the subsurface resistivity.
4. Data Interpretation: The collected data are used to create resistivity models of the subsurface. Different materials in the Earth's crust affect the electromagnetic fields in distinct ways, allowing geophysicists to map variations in resistivity and infer geological structures.
Types of Magneto Telluric Measurements:
1. Audio-Magneto telluric (AMT): Measures frequencies in the audio range (from about 1 Hz to 1000 Hz). It is useful for exploring shallow to intermediate depths (up to a few kilometers).
2. Broadband Magneto telluric: Measures a wide range of frequencies, from extremely low frequencies (ELF) to high frequencies (HF). This approach provides a comprehensive view of resistivity from shallow to deep levels (up to tens of kilometers).
3. Very Low Frequency (VLF) Electromagnetic Methods: Measures electromagnetic fields at frequencies below 30 kHz. While not strictly MT, VLF methods can be used for shallow investigations and complement MT data.
Applications of Magneto Telluric:
1. Mineral Exploration: Identifies and maps subsurface mineral deposits, including those of metal ores and other valuable minerals.
2. Geothermal Energy: Helps in locating geothermal reservoirs by mapping the thermal structure and identifying areas with high resistivity associated with geothermal activity.
3. Hydrogeology: Assists in identifying and mapping aquifers and groundwater resources by detecting variations in subsurface resistivity related to water content.
4. Oil and Gas Exploration: Aids in understanding subsurface structures and fluid reservoirs, although it is less commonly used compared to other methods like seismic surveys.
5. Environmental Studies: Helps in monitoring and assessing contamination and changes in subsurface conditions due to environmental impacts.
6. Tectonics and Geodynamics: Provides information on large-scale geological structures such as faults, crustal thickness, and mantle composition, contributing to the understanding of tectonic processes and plate dynamics.
Advantages of Magneto Telluric:
1. Deep Penetration: Can probe the Earth's subsurface to great depths, often reaching tens of kilometers.
2. Non-Invasive: Does not require drilling or physical contact with the subsurface, making it suitable for large-scale and sensitive investigations.
3. Versatile: Applicable in a variety of geological settings and for different types of subsurface investigations.
Limitations of Magneto Telluric:
1. Data Complexity: Interpretation of MT data can be complex and requires sophisticated modeling techniques.
2. Environmental Noise: Measurements can be affected by electrical noise from power lines, electronic equipment, and other sources, which can complicate data acquisition and interpretation.
3. Resolution: The resolution of the method can be limited by the scale of the survey and the frequency range used.
Typical MT Equipment:
1. Electric Field Sensors: Measure the electric fields on the Earth's surface, usually involving electrodes placed at specific intervals.
2. Magnetic Field Sensors: Measure the magnetic fields, often using fluxgate or induction magnetometers.
3. Data Acquisition System: Records the measurements and processes the data for analysis.
Magneto telluric is a powerful tool for subsurface exploration and geological research, providing valuable insights into the Earth's structure and composition through the analysis of natural electromagnetic fields.
Certainly! Here are some questions related to Magneto telluric (MT) in geophysics:
1. What is the primary purpose of using Magneto telluric (MT) in geophysics?
The primary purpose of using MT in geophysics is to investigate the Earth's subsurface by measuring natural variations in the Earth's magnetic and electric fields to infer the distribution of resistivity and identify geological structures.
2. How do MT methods measure the subsurface resistivity?
MT methods measure the ratio of the electric field to the magnetic field at various frequencies. By analyzing these measurements, geophysicists can infer the resistivity of subsurface materials, as different materials affect the electromagnetic fields differently.
3. What are the typical frequency ranges used in Magneto telluric (MT) surveys, and what depth ranges do they correspond to?
MT surveys typically use frequencies ranging from a few Hz to several kHz. Lower frequencies are used for deeper investigations (up to tens of kilometers), while higher frequencies are suitable for shallower depths (up to a few kilometers).
4. What are the main types of sensors used in Magneto telluric surveys, and what do they measure?
The main types of sensors used in MT surveys are electric field sensors (electrodes) that measure variations in the electric field and magnetic field sensors (magnetometers) that measure variations in the magnetic field.
5. How does the presence of high electrical conductivity materials, such as saline water, affect Magneto telluric measurements?
High electrical conductivity materials, such as saline water, can significantly affect Magneto telluric measurements by increasing the attenuation of the electromagnetic waves, leading to lower resistivity readings and potentially obscuring deeper geological features.
6. What are some common applications of Magneto telluric in environmental and resource exploration?
Common applications of MT include mapping geothermal reservoirs, identifying and characterizing mineral deposits, assessing groundwater resources, and monitoring subsurface contamination and environmental changes.
7. What are the main challenges associated with interpreting Magneto telluric data?
Main challenges include dealing with environmental noise, differentiating between different subsurface structures, and complex data interpretation due to the varying effects of geological features on electromagnetic fields.
8. How does Magneto telluric compare to other geophysical methods, such as seismic surveys or electrical resistivity tomography, in terms of depth penetration and resolution?
Magneto telluric typically offers greater depth penetration (tens of kilometers) compared to methods like seismic surveys or electrical resistivity tomography, which are often limited to shallower depths. However, MT may have lower resolution in some cases, especially in highly conductive environments.
9. In what geological settings is Magneto telluric particularly useful, and why?
MT is particularly useful in geological settings such as arid regions, where electrical resistivity methods might struggle due to low conductivity, and in areas with significant geothermal activity or complex subsurface structures, where MT can provide deep, detailed resistivity profiles.
10. What are the typical data processing and modeling techniques used in Magneto telluric to interpret the results?
Typical data processing and modeling techniques in MT include Fourier transforms to convert time-domain data to frequency-domain, 1D and 2D inversion algorithms to create resistivity models, and forward modeling to simulate how electromagnetic waves interact with subsurface structures.
These questions cover a range of fundamental concepts and practical applications related to Magneto telluric in geophysics.