Some important questions of GATE GG

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1. Geology: Structural Geology

Question (2021):
A fault has a dip of 45° and a rake of 60° on the fault plane. What is the slip direction relative to the horizontal plane?

Explanation:

Step 1: Rake (pitch) is the angle between the slip direction and the horizontal line within the fault plane.

Step 2: A rake of 60° on a fault plane dipping 45° indicates that the slip is inclined at 60° to the horizontal.

Answer: The slip direction relative to the horizontal is 60°.



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2. Geology: Mineralogy

Question (2020):
Identify the mineral from the following XRD peak positions:
2θ values: 21.5°, 27.9°, 50.2°.
Options:
a) Quartz
b) Feldspar
c) Calcite
d) Halite

Explanation:

Step 1: Match the given 2θ values with standard XRD patterns.

Step 2: These values correspond to quartz (SiO₂) based on its primary diffraction peaks.

Answer: a) Quartz.



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3. Geology: Paleontology

Question (2019):
What is the fossil group primarily used for Paleozoic stratigraphy?
Options:
a) Trilobites
b) Ammonites
c) Foraminifera
d) Echinoids

Explanation:

Trilobites are an index fossil for the Paleozoic Era due to their widespread distribution and rapid evolution.

Ammonites are mainly used for Mesozoic stratigraphy.

Answer: a) Trilobites.

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4. Geophysics: Gravity and Magnetics

Question (2020):
A gravity anomaly is observed to be -10 mGal over a sedimentary basin. What does this indicate about the density contrast?
Options:
a) Positive
b) Negative
c) Zero
d) Cannot be determined

Explanation:

A negative gravity anomaly indicates that the subsurface material has a lower density than the surrounding rock.

Answer: b) Negative.


5. Geology - Structural Geology

Question:

The plunge of a fold axis is measured as 30°. What type of fold is this?
a) Gentle
b) Moderate
c) Steep
d) Recumbent

Explanation:

The classification of folds based on the plunge of the fold axis:

Gentle: Plunge 0°–10°

Moderate: Plunge 10°–30°

Steep: Plunge >30°


Since the given plunge is 30°, the fold is moderate.

Answer:

b) Moderate


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6. Geophysics - Seismology

Question:

A seismic P-wave has a velocity of 6.0 km/s in a given medium, while the S-wave velocity in the same medium is 3.5 km/s. Calculate the Poisson’s ratio.

Explanation:

Poisson’s ratio (ν) can be calculated using the formula:


Substitute  and :

\nu = \frac{1 - 2\left(\frac{3.5}{6.0}\right)^2}{2\left(1 - \left(\frac{3.5}{6.0}\right)^2\right)}

\nu = \frac{1 - 2(0.583)^2}{2(1 - (0.583)^2)}
]

\nu = \frac{1 - 2(0.34)}{2(1 - 0.34)}

\nu = \frac{1 - 0.68}{2(0.66)} = \frac{0.32}{1.32} \approx 0.24
]

Answer:

Poisson’s ratio = 0.24

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