Gravity Method in Geophysics

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Questions and Answers

What is the main characteristic of the gravity geophysical method?

Invasive and destructive

Active and expensive

Invasive and expensive

Non-invasive and passive (correct)

What physical property controls the changes in the Earth's gravitational field?

Density (correct)

Thermal conductivity

Magnetic susceptibility

Electrical conductivity

What type of geological structure can be detected by the gravity geophysical method?

Anticline (correct)

Syncline

Fault

Volcanic cone

What is the primary use of the gravity geophysical method?

Oil exploration Signup and view all the answers

What type of geological feature can be effectively mapped using the gravity geophysical method?

Sedimentary basins Signup and view all the answers

What is the reason why the gravity geophysical method is suitable for locating salt bodies?

Salt has a lower density than surrounding formations Signup and view all the answers

What is the primary application of microgravity profiling?

Detecting voids or submerged features Signup and view all the answers

What is the main principle behind the magnetic method?

Detecting distortions in the Earth's magnetic field Signup and view all the answers

What type of materials can be detected using the magnetic method?

Ferrous materials Signup and view all the answers

What is the purpose of the spring balance in microgravity profiling?

To measure relative shifts in the Earth's gravitational field Signup and view all the answers

What is a common application of the magnetic method?

Detecting buried metallic objects Signup and view all the answers

What is a benefit of using microgravity profiling?

It can detect voids or submerged features Signup and view all the answers

What is the primary purpose of airborne surveys in geological exploration?

To provide information for the initial stages of exploration Signup and view all the answers

What is the primary source of energy used in seismic surveys?

Truck-mounted vibrating weights Signup and view all the answers

What type of surveys measure the variations of the Earth's magnetic field?

Magnetic surveys Signup and view all the answers

What type of surveys are particularly suited to flat-lying sedimentary basins?

Seismic surveys Signup and view all the answers

What type of surveys measure the naturally occurring radiation from potassium, thorium, and uranium?

Radiometric surveys Signup and view all the answers

What type of surveys measure the variations in rock density in the Earth's crust?

Gravity surveys Signup and view all the answers

Study Notes

Gravity Method

Non-invasive, non-destructive, and relatively inexpensive
Passive, meaning no energy needs to be put into the ground to acquire data
Studies subsurface geology using changes in the Earth's gravitational field caused by differences in density between subsurface rocks

Physical Property

Density is the controlling physical property
Different types of rock have different densities, and denser rocks have greater gravitational attraction
Higher-density formations arched upward in a structural high, such as an anticline, increase the Earth's gravitational field over the axis of the structure compared to its flanks

Uses

Mainly used for oil exploration
Sometimes used in mineral and groundwater prospecting
Effective for mapping sedimentary basins where the basement rocks have a higher density than the sediments
Suitable for locating and mapping salt bodies due to the low density of salt compared to surrounding formations
Used for direct detection of heavy minerals such as chromite

Types of Gravity Geophysical Methods

Microgravity Profiling

Passive technique that measures relative shifts in the Earth's gravitational field with extreme precision
Uses a gravity meter to take measurements
Can identify voids or submerged features like underground storage tanks due to subtle changes in gravity caused by density differences

Magnetic Method

Obtains information related to the direction, gradient, or intensity of the Earth's magnetic field
Measures distortions in the Earth's magnetic field caused by ferrous materials
Used for large-scale geology mapping, detecting buried metallic objects, and detecting some geologic features like lava tubes

Ground-Based Surveys

Seismic Surveys

Measure variations in reflected ground vibrations as they pass through the earth
Use an energy source to create high-frequency vibrations
Provide information about rocks down to depths of several kilometers
Particularly suited to flat-lying sedimentary basins
Most often used in petroleum and coal exploration

Magnetic Surveys

Measure variations of the Earth's magnetic field due to the presence of magnetic minerals
Subtle variations in magnetic minerals are used to interpret rock types and identify resources
Most often used in metallic mineral exploration

Radiometric Surveys

Measure gamma rays continuously emitted from the Earth by natural decomposition of radiogenic minerals
Focus on recording naturally occurring radiation from potassium, thorium, and uranium
Most often used in metallic and industrial mineral exploration

Gravity Surveys

Measure the gravity field with a gravimeter to determine variations in rock density in the Earth's crust

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Description

Learn about the gravity method, a non-invasive and non-destructive remote sensing technique used to study subsurface geology. Understand how it works and its applications.