(B) To detect and map subsurface geological structures Explanation: Magnetic methods in geophysics are primarily used to detect and map subsurface geological structures by measuring variations in the Earth's magnetic field caused by different rock types and mineral content.

(B) Magnetometer Explanation: A magnetometer is the instrument commonly used in geophysical surveys to measure the Earth's magnetic field and detect magnetic anomalies.

(B) Faster data collection over large areas Explanation: The primary advantage of aeromagnetic surveys is their ability to collect data quickly over large areas, making them efficient for regional-scale geological mapping.

(B) The temperature at which magnetic minerals lose their magnetism Explanation: The Curie temperature is the temperature at which magnetic minerals lose their permanent magnetism, becoming paramagnetic.

(C) Mid-ocean ridges Explanation: Magnetic anomalies detected in marine environments are often associated with mid-ocean ridges, where new oceanic crust is formed and records the Earth's magnetic field.

(C) Mapping iron ore deposits Explanation: Magnetic surveys are commonly used in mineral exploration to map iron ore deposits due to the strong magnetic properties of iron minerals.

(B) The difference between the measured magnetic field and the theoretical magnetic field Explanation: The total field anomaly refers to the difference between the measured magnetic field and the theoretical magnetic field, indicating variations caused by subsurface structures.

(B) Magnetometer Explanation: A magnetometer is the instrument used to measure the magnetic properties of rocks in paleomagnetic studies. It can detect the strength and direction of magnetic fields.

(B) The degree to which a material can be magnetized Explanation: Magnetic susceptibility is a measure of how easily a material can be magnetized by an external magnetic field, indicating the concentration of magnetic minerals within the material.

(B) Using a base station magnetometer Explanation: A base station magnetometer is used to monitor and record diurnal variations in the Earth's magnetic field, allowing for corrections to be applied to the survey data to account for these natural fluctuations.

(B) To map variations in the Earth's magnetic field at the surface Explanation: The primary objective of a ground magnetic survey is to map variations in the Earth's magnetic field at the surface, which can reveal subsurface geological structures and mineral deposits.

(C) The combined strength of all magnetic field components Explanation: The total magnetic field intensity is the combined strength of all components of the Earth's magnetic field, including vertical and horizontal elements, measured at a specific location.

(C) Accurate measurement of weak magnetic fields Explanation: Fluxgate magnetometers are highly sensitive instruments capable of accurately measuring weak magnetic fields, making them ideal for detailed magnetic surveys.

(B) A fault filled with non-magnetic sediments Explanation: A fault filled with non-magnetic sediments can create a negative magnetic anomaly because the sediments do not contribute to the magnetic field, resulting in a weaker magnetic signal compared to the surrounding rocks.

(C) It provides the angle between magnetic north and true north Explanation: Magnetic declination is the angle between magnetic north and true north at a specific location, which is important for accurately interpreting magnetic survey data.

MCQ on Magnetic Methods in Geophysics – Miscellaneous

16. How can magnetic methods be used in environmental studies?

(A) By measuring soil moisture content
(B) By detecting buried waste and contamination
(C) By analysing plant growth patterns
(D) By studying weather patterns

(B) By detecting buried waste and contamination
Explanation: Magnetic methods can be used in environmental studies to detect buried waste and contamination, as certain materials and pollutants may create distinctive magnetic anomalies that can be mapped and analysed.

17. What is the term for a line on a magnetic map that connects points of equal magnetic intensity?

(A) Contour line
(B) Isochron
(C) Isoline
(D) Isodynamic line

(D) Isodynamic line
Explanation: An Isodynamic line is a line on a magnetic map that connects points of equal magnetic intensity, helping to visualize the distribution of magnetic anomalies.

18. What is the purpose of using a gradiometer in magnetic surveys?

(A) To measure temperature gradients
(B) To measure magnetic field gradients
(C) To record seismic waves
(D) To detect electrical conductivity

(B) To measure magnetic field gradients
Explanation: A gradiometer is used in magnetic surveys to measure the gradients of the magnetic field, providing detailed information about the rate of change in magnetic intensity over short distances.

19. Which of the following can cause a magnetic anomaly?

(A) A change in atmospheric pressure
(B) A subsurface rock formation with different magnetic properties
(C) A variation in surface temperature
(D) An increase in groundwater levels

(B) A subsurface rock formation with different magnetic properties
Explanation: A magnetic anomaly can be caused by a subsurface rock formation with different magnetic properties, resulting in a variation in the Earth’s magnetic field at that location.

20. How can magnetic methods help in identifying fault zones?

(A) By measuring seismic wave velocities
(B) By detecting changes in magnetic susceptibility
(C) By analysing soil moisture content
(D) By recording thermal anomalies

(B) By detecting changes in magnetic susceptibility
Explanation: Magnetic methods can help identify fault zones by detecting changes in magnetic susceptibility, as faults often juxtapose rocks with different magnetic properties.

21. What is the primary component of the Earth’s magnetic field that is measured in magnetic surveys?

(A) The horizontal component
(B) The vertical component
(C) The total field intensity
(D) The dip angle

(C) The total field intensity
Explanation: The primary component of the Earth’s magnetic field measured in magnetic surveys is the total field intensity, which includes contributions from both the horizontal and vertical components.

22. What is the role of a base station in a magnetic survey?

(A) To provide a fixed reference point for magnetic measurements
(B) To record seismic data
(C) To monitor weather conditions
(D) To measure electrical conductivity

(A) To provide a fixed reference point for magnetic measurements
Explanation: A base station in a magnetic survey provides a fixed reference point for magnetic measurements, allowing for the correction of diurnal variations and other temporal changes in the Earth’s magnetic field.

23. Which type of rock is typically associated with strong magnetic anomalies due to its high iron content?

(A) Limestone
(B) Sandstone
(C) Granite
(D) Basalt

(D) Basalt
Explanation: Basalt is typically associated with strong magnetic anomalies due to its high iron content, which contributes to its strong magnetic properties.

24. What is the primary advantage of using magnetic surveys in unexplored regions?

(A) Low cost and rapid data collection
(B) High resolution of subsurface features
(C) Ability to measure electrical conductivity
(D) Direct detection of oil and gas reserves

(A) Low cost and rapid data collection
Explanation: The primary advantage of using magnetic surveys in unexplored regions is their low cost and rapid data collection, making them an efficient method for preliminary geological exploration.

25. How can magnetic methods be used to study ancient human activities?

(A) By measuring atmospheric carbon levels
(B) By detecting buried structures and artifacts
(C) By analysing tree ring patterns
(D) By studying ocean currents

(B) By detecting buried structures and artifacts
Explanation: Magnetic methods can be used to study ancient human activities by detecting buried structures and artifacts, as these often cause magnetic anomalies that can be mapped and analysed.

26. What is the term for a line on a magnetic map that connects points of equal magnetic declination?

(A) Agonic line
(B) Isogonic line
(C) Isoclinic line
(D) Isodynamic line

(B) Isogonic line
Explanation: An Isogonic line is a line on a magnetic map that connects points of equal magnetic declination.

27. What is the term for a line on a magnetic map that connects points of equal magnetic dip?

(A) Aclinic line
(B) Isogonic line
(C) Isoclinic line
(D) Isodynamic line

(C) Isoclinic line
Explanation: An Isoclinic line is a line on a magnetic map that connects points of equal magnetic dip.

28. The lines connecting points of zero magnetic declination on a magnetic map is known as

(A) Agonic line
(B) Isogonic line
(C) Isoclinic line
(D) Isodynamic line

(A) Agonic line
Explanation: An Agonic line is a line on a magnetic map that connects points of zero magnetic declination.

29. The lines connecting points of zero magnetic dip on a magnetic map is known as

(A) Agonic line
(B) Isogonic line
(C) Isoclinic line
(D) Aclinic line

(D) Aclinic line
Explanation: An Aclinic line is a line on a magnetic map that connects points of zero magnetic dip.

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MCQ on Magnetic Methods in Geophysics – Miscellaneous

16. How can magnetic methods be used in environmental studies?

17. What is the term for a line on a magnetic map that connects points of equal magnetic intensity?

18. What is the purpose of using a gradiometer in magnetic surveys?

19. Which of the following can cause a magnetic anomaly?

20. How can magnetic methods help in identifying fault zones?

21. What is the primary component of the Earth’s magnetic field that is measured in magnetic surveys?

22. What is the role of a base station in a magnetic survey?

23. Which type of rock is typically associated with strong magnetic anomalies due to its high iron content?

24. What is the primary advantage of using magnetic surveys in unexplored regions?

25. How can magnetic methods be used to study ancient human activities?

26. What is the term for a line on a magnetic map that connects points of equal magnetic declination?

27. What is the term for a line on a magnetic map that connects points of equal magnetic dip?

28. The lines connecting points of zero magnetic declination on a magnetic map is known as

29. The lines connecting points of zero magnetic dip on a magnetic map is known as

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