This set of Engineering Geology Multiple Choice Questions & Answers (MCQs) focuses on “The Crust”.
1. What is the thickness of the crust under the mountainous areas and in particular the Himalayas?
a) 50-55 km
b) 60-65 km
c) 70-75 km
d) 30-35 km
Explanation: It is believed that the thickness of the crust under the Himalayas is 70 to 75 km and under the Hindukush it is said to be 60 km thick.
2. The discontinuity which marks the lower boundary of the crust is
a) Crust-Mantle discontinuity
b) Oceanic discontinuity
c) SIAL layer
d) Mohorovicic discontinuity
Explanation: Mohorovicic discontinuity marks the lower boundary of the crust which is the first layer of the Earth.
3. The granite layer in the crust is also referred to as
Explanation: SIAL stands for Silicon and Aluminium and as per the name it is made up of the two elements and hence the name.
4. The density of the oceanic layer in the crust is said to be
a) 3.00 g/cc
b) 2.50 g/cc
c) 1.90 g/cc
d) 2.00 g/cc
Explanation: The oceanic crust is estimated to have a volume of 2.54*109 cc with an average density of 3.00 g/cc.
5. The depth at which the Mohorovicic discontinuity occurs is
a) 90-100 km
b) 50-60 km
c) 70-80 km
d) 30-40 km
Explanation: Mohorovicic discontinuity from seismic evidence is determined that it is approximately at a depth of 30-40 km.
6. What is the speed attained by the P-waves in the C-layer under the Continental crust?
a) 6 to 7.6 km/sec
b) 3 to 4 km/sec
c) 5 to 6.3 km/sec
d) 1.8 to 2.5 km/sec
Explanation: The C-layer is the lowermost layer of the continental crust and here the P-waves attain velocity as high as 6 to 7.6 km/sec.
7. The layer under the continental crust with the density of 2.4 to 2.6 g/cc
Explanation: The Middle layer or B-layer of the continental crust is relatively dense compared to A-layer and the density is said to be 2.4 to 2.6 g/cc.
8. The expansion of SIMA is
a) Silicon and Manganese
b) Silicon and Magnesium
c) Strontium and Manganese
d) Strontium and Magnesium
Explanation: Silicon and Magnesium. The C-layer under the continental crust is rich in Silicon and Magnesium and hence the layer is also sometimes called SIMA.
9. The oceanic layer is the extension of C-layer of the continental crust and A and B-layer are mostly absent. State whether true or false.
Explanation: The oceanic crust is the extension of C-layer of the continental crust that makes the top layer of the oceans in most cases, A and B layers being practically absent from there.
10. The least dense layer among the layers under the continental crust is
Explanation: The A or the upper layer is between 2 to 10 km thick and is of low density, 2.00 g/cc.
11. The area not considered under the crust is
a) Mountainous area
b) Continental area
c) Oceanic area
d) Glacial area
Explanation: The first the options, Mountainous, Continental and Oceanic areas are studied separately whereas Glacial area is not considered under study of the crust as such.
Sanfoundry Global Education & Learning Series – Engineering Geology.
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