# Earthquake Engineering Questions and Answers – Internal Structure of Earth

This set of Earthquake Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Internal Structure of Earth”.

1. The crust and mantle are not a part of which of these surfaces of earth?
a) Lithosphere
b) Asthenosphere
c) Mesosphere
d) Bryosphere

Explanation: Lithosphere, Asthenosphere and mesosphere are part of the crust and the mantle whereas the core is a part of the Bryosphere. The lithosphere is the outer-most layers and divided into 15 tectonics plates. Majority of the earthquakes and volcanic activities occur at the boundaries of these tectonic plates.

2. The outer core of the earth is in which state?
a) Fluid
b) Solid
c) Gaseous
d) Undefined

Explanation: The outer core of the earth is composed of iron and nickel in a molten state. The thickness of this layer is about 2400 Km. The inner core is a solid ball of iron-nickel alloy of about 1220 Km diameter.

3. Which if these seismic waves do not pass through the outer core?
a) Bending waves
b) Shear waves
c) Rayleigh waves
d) Love waves

Explanation: Shear waves pass through a medium by shearing action of the medium particles. The outer core is made up of fluid which has negligible shear stress. Hence shear waves do not pass through the core.

4. The outer core has a thickness of about __________________
a) 2.4 Km
b) 240 Km
c) 2400 Km
d) 24000 Km

Explanation: The thickness of outer core is 2400 KM. It is composed of alloys of iron and nickel in a molten state. It is located at a distance of about 2890 Km form the earth’s surface. The evidence for the presence of this fluid layer was found after studying the propagation of shear waves through the interior of the earth.

5. The depth at which there is a sudden increase in the velocity of P-waves is called as ___________
a) Mohorovicic discontinuity
c) Lehmann discontinuity
d) Gutenberg discontinuity.

Explanation: Mohorovicic discovered that in the Croatia earthquake, only direct P-waves were recorded from the epicentre. However, at a distance of 100Km from the epicentre two waves were recorded as a result of refraction at the discontinuity between the mantle and crust. This wave resulted in a sudden increase in the velocity of the seismic wave from the epicentre.

6. The interface that separates the upper crust and lower crust is called as ____________________
b) Lehmann discontinuity
c) Gutenberg discontinuity
d) Mohorovicic discontinuity

Explanation: V. Conrad in 1925 inferred the existence of two cluster masses the upper and the lower crust. In honour of the work done by him the interface separating the discontinuities is termed as Conrad discontinuity.

7. Which of these layers is made up of oxides of iron and nickel and perovskite nature of iron and magnesium silicates?
a) Upper mantle
b) Lower mantle
c) Inner core
d) Crust

Explanation: The lower mantle is made up of oxides of iron and nickel. The upper mantle is made up if olivine rock, iron magnesium and silicate compounds. The inner core is composed of gold, platinum and siderophile elements. Crust is made up of oxygen, silicon, iron, potassium.

8. The core mantle boundary is known as ________________
b) Gutenberg discontinuity
c) Lehman discontinuity
d) Oldham discontinuity

Explanation: This type of discontinuity was reported by Gutenberg in the year 1914. He also located the depth of the outer core from the ground surface by studying the seismic waves. In his honour the discontinuity was named as Gutenberg discontinuity.

9. The zone in the interior of the earth surface wherein the velocity of the primary ways drops down suddenly is called as ______________
b) No velocity zones
c) Null zone
d) Zero zone

Explanation: The velocity of the P-waves drops down suddenly in the shadow zone. It exists in an epicentre range of 105 to 143 degree. In this zone the seismographs can hardly detect an earthquake. This zone is created because of the refraction of the primary waves by the outer core of the earth.

10. The net radius of the earth is __________________
a) 640 Km
b) 6400 Km
c) 64000 Km
d) 6400 feet

Explanation: The net radius of the earth is 6400 Km. It consists of a crust, a mantle up to a depth of 5 Km and two cores from a depth of 5000 Km to 6400 Km. The radius of the earth has been determined by extensive study of seismic wave propagation and the same has been verified by volcanic activities and bathymetry.

Sanfoundry Global Education & Learning Series – Earthquake Engineering.

To practice all areas of Earthquake Engineering, here is complete set of Multiple Choice Questions and Answers.

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