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(B) To measure variations in Earth's gravitational field Explanation: Gravity methods are used to measure small variations in Earth's gravitational field to study subsurface structures, such as ore bodies, voids, and sedimentary basins. These variations are caused by differences in the density of underlying materials.

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(B) Gravimeter Explanation: A gravimeter is a highly sensitive instrument used to measure gravitational acceleration. It detects minute variations in the gravitational field that provide insights into subsurface structures.

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(B) Milligal Explanation: Gravity variations are typically measured in milligals (mGal), a smaller unit of gravitational acceleration suitable for detecting minute changes.

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(C) Higher density increases gravitational acceleration Explanation: Dense materials exert a stronger gravitational pull, causing a positive gravity anomaly in measurements.

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(B) Presence of voids or low-density material Explanation: Negative gravity anomalies suggest regions with lower density, such as sedimentary basins or voids, which reduce gravitational acceleration.

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(B) Terrain correction Explanation: Terrain correction adjusts gravity measurements to account for the influence of nearby topographical features on gravitational readings.

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(C) A dense igneous intrusion Explanation: Dense materials, such as igneous intrusions, cause a positive gravity anomaly because they increase gravitational acceleration in the region.

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(B) Cost-effectiveness and passive nature Explanation: Gravity methods are relatively low-cost and passive (do not require active sources like seismic surveys), making them suitable for preliminary geological studies.

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(B) The rate of change of gravity with distance Explanation: A gravity gradient refers to the spatial rate of change of gravitational acceleration, which can provide detailed information about subsurface density variations.

Question 1

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(B) To measure variations in Earth's gravitational field
Explanation: Gravity methods are used to measure small variations in Earth's gravitational field to study subsurface structures, such as ore bodies, voids, and sedimentary basins. These variations are caused by differences in the density of underlying materials.

Question 2

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Accepted Answer

(B) Gravimeter
Explanation: A gravimeter is a highly sensitive instrument used to measure gravitational acceleration. It detects minute variations in the gravitational field that provide insights into subsurface structures.

Question 3

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Accepted Answer

(B) Milligal
Explanation: Gravity variations are typically measured in milligals (mGal), a smaller unit of gravitational acceleration suitable for detecting minute changes.

Question 4

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Accepted Answer

(C) Higher density increases gravitational acceleration
Explanation: Dense materials exert a stronger gravitational pull, causing a positive gravity anomaly in measurements.

Question 5

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Accepted Answer

(B) Presence of voids or low-density material
Explanation: Negative gravity anomalies suggest regions with lower density, such as sedimentary basins or voids, which reduce gravitational acceleration.

Question 6

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Accepted Answer

(B) Terrain correction
Explanation: Terrain correction adjusts gravity measurements to account for the influence of nearby topographical features on gravitational readings.

Question 7

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(C) A dense igneous intrusion
Explanation: Dense materials, such as igneous intrusions, cause a positive gravity anomaly because they increase gravitational acceleration in the region.

Question 8

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Accepted Answer

(B) A corrected gravity value accounting for terrain and elevation
Explanation: The Bouguer anomaly is the gravitational measurement corrected for the effects of terrain and elevation. It helps isolate the gravitational effect of subsurface density variations.

Question 9

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Accepted Answer

(B) Cost-effectiveness and passive nature
Explanation: Gravity methods are relatively low-cost and passive (do not require active sources like seismic surveys), making them suitable for preliminary geological studies.

Question 10

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Accepted Answer

(B) The rate of change of gravity with distance
Explanation: A gravity gradient refers to the spatial rate of change of gravitational acceleration, which can provide detailed information about subsurface density variations.

Question 11

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Accepted Answer

(C) Latitude correction
Explanation: The latitude correction accounts for variations in gravitational acceleration caused by the Earth's oblate shape and rotation, which result in slightly different gravity values at different latitudes.

Question 12

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(A) Limited resolution for small-scale features
Explanation: Gravity methods have low resolution for small-scale or shallow features, as they are better suited for detecting broader density variations in the subsurface.

Question 13

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(B) It accounts for the elevation of the measurement point above sea level
Explanation: Free-air correction adjusts gravity measurements for the effect of altitude, assuming the absence of any intervening material, to normalize readings to sea level.

Question 14

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(B) A sediment-filled basin
Explanation: Sediment-filled basins have lower densities than surrounding rocks, leading to a strong negative Bouguer anomaly.

Question 15

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(B) An anomaly caused by deep-seated geological structures
Explanation: Regional anomalies are broad, low-frequency variations in gravity data that arise from deep-seated geological structures, as opposed to local anomalies caused by shallow features.

Question 16

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(B) In Bouguer anomaly maps
Explanation: Gravity data are typically processed and displayed as Bouguer anomaly maps, which help geophysicists identify variations in subsurface density.

Question 17

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(B) Mapping subsurface density variations on a small scale
Explanation: Microgravity surveys are highly sensitive and used for detecting small-scale density variations, such as voids, tunnels, or small ore bodies.

Question 18

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(D) Magnetic field intensity
Explanation: Gravity measurements are influenced by factors like density, rotation, and topography but are independent of Earth's magnetic field intensity.

Question 19

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(B) Negative anomaly
Explanation: Salt domes have lower densities than the surrounding rocks, resulting in a negative gravity anomaly in measurements.

Question 20

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(C) Earth's mass and density distribution
Explanation: The Earth's gravitational field is generated by its mass and the density distribution within the planet. Variations in subsurface density cause measurable changes in the gravitational field.

Question 21

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(B) To account for topographic irregularities near the measurement site
Explanation: Terrain correction adjusts for the gravitational influence of nearby hills and valleys, ensuring that the gravity data accurately reflect subsurface density variations.

Question 22

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(B) A localized gravity anomaly after removing regional trends
Explanation: Residual anomalies are localized variations in gravity data after subtracting regional trends, often indicating near-surface features.

Question 23

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(C) A metallic ore body
Explanation: Dense materials, such as metallic ore bodies, increase the gravitational acceleration, resulting in a positive gravity anomaly.

Question 24

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(B) To compensate for variations due to Earth's shape and rotation
Explanation: Gravity varies with latitude because the Earth is not a perfect sphere (it is an oblate spheroid), and its rotation slightly reduces gravity at the equator compared to the poles.

Question 25

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(B) Gravity decreases with distance
Explanation: Gravity decreases with the square of the distance from the Earth's center, as described by Newton's law of gravitation.

Question 26

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(A) Gravitational acceleration values
Explanation: Gravity surveys collect data on variations in gravitational acceleration, which are used to infer subsurface density differences.

Question 27

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(B) To identify low-density sedimentary basins
Explanation: Gravity methods are used to detect low-density sedimentary basins that may contain petroleum deposits.

Question 28

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(C) Positive anomaly
Explanation: High-density subsurface features, such as igneous intrusions, create positive gravity anomalies due to their stronger gravitational pull.

Question 29

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(A) Drift correction
Explanation: Drift correction is applied to gravity data to remove errors caused by gradual changes in the sensitivity of the gravimeter over time.

Question 30

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(B) To correct for the mass of the topography above the measurement point
Explanation: The Bouguer correction removes the gravitational effect of the mass between the measurement point and sea level, ensuring that gravity readings reflect subsurface features.

Question 31

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(C) Over a sedimentary basin
Explanation: Sedimentary basins typically have lower densities compared to surrounding rocks, resulting in gravity lows.

Question 32

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(A) Gravimeter
Explanation: A gravimeter is a sensitive instrument used to measure variations in gravitational acceleration at different locations.

Question 33

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(B) Because gravity variations on Earth are small and require finer units
Explanation: Earth's gravity variations are typically in the range of milligals, necessitating the use of smaller units for accurate representation.

Question 34

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(B) To locate subsurface density variations indicating ore bodies
Explanation: Gravity surveys help identify density contrasts in the subsurface, which may indicate the presence of mineral deposits.

Question 35

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(B) A corrected value accounting for elevation but not density
Explanation: A free-air anomaly is the gravity measurement corrected for elevation differences, assuming there is no material between the measurement point and sea level.

Question 36

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(B) The poles
Explanation: Gravity is strongest at the poles due to Earth's oblate shape and centrifugal force reduction from rotation.

Question 37

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(B) Rapid coverage of large areas
Explanation: Airborne gravity surveys are efficient for covering large and inaccessible areas quickly, although they provide less resolution compared to ground-based surveys.

Question 38

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(B) Thicker crust causes lower gravity values
Explanation: Thicker crust generally has lower density compared to the mantle, resulting in lower gravity values over regions with thicker crust.

Question 39

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(B) Detecting small-scale density variations like voids or tunnels
Explanation: Microgravity surveys are highly sensitive and used for detecting small-scale subsurface features such as voids, cavities, or archaeological structures.

Question 40

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Detecting small-scale density variations like voids or tunnels
Explanation: Microgravity surveys are highly sensitive and used for detecting small-scale subsurface features such as voids, cavities, or archaeological structures.

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