Q1: Multiple choice questions.
(i) Which one of the following earthquake waves is more destructive?
(a) P-waves
(b) S-waves
(c) Surface waves
(d) None of the above
Ans: (c)
(ii) Which one of the following is a direct source of information about the interior of the earth?
(a) Earthquake waves
(b) Volcanoes
(c) Gravitational force
(d) Earth magnetism
Ans: (b)
(iii) Which type of volcanic eruptions have caused Deccan Trap formations?
(a) Shield
(b) Flood
(c) Composite
(d) Caldera
Ans: (b)
(iv) Which one of the following describes the lithosphere:
(a) upper and lower mantle
(b) crust and upper mantle
(c) crust and core
(d) mantle and core
Ans: (b)
Q2: Answer the following questions in about 30 words.
(i) What are body waves?
Ans: Body waves are those earthquake waves, which are generated due to release of energy at the focus and move in all directions travelling through the body of the earth.
(ii) Name the direct sources of information about the interior of the earth.
Ans: Rocks obtained from mining areas and materials obtained from volcanic eruption are the direct sources of information about the interior of the earth.
(iii) Why do earthquake waves develop shadow zone?
Ans: A seismic shadow zone is an area of the Earth's surface where seismographs cannot detect an earthquake after its seismic waves have passed through the Earth. It was observed that seismographs located at any distance within 105° from the epicentre, recorded the arrival of both P and S-waves. However, a zone between 105° and 145° from epicentre was identified as the shadow zone for both the types of waves.
(iv) Briefly explain the indirect sources of information of the interior of the earth other than those of seismic activity.
Ans: The indirect sources of information of the interior of the earth are:
Q3: Answer the following questions in about 150 words.
(i) What are the effects of propagation of earthquake waves on the rock mass through which they travel?
Ans: The earthquake waves cause vibration in the body of the rocks through which they pass. P-waves vibrate parallel to the direction of the wave. This exerts pressure on the material in the direction of the propagation. As a result, it creates density differences in the material leading to stretching and squeezing of the material. Other three waves vibrate perpendicular to the direction of propagation. The direction of vibrations of S-waves is perpendicular to the wave direction in the vertical plane. Hence, they create troughs and crests in the material through which they pass. Surface waves are considered to be the most damaging waves.
(ii) What do you understand by intrusive forms? Briefly describe various intrusive forms.
Ans: The lava that is released during volcanic eruptions on cooling develops into igneous rocks. These forms are called intrusive forms.
Various intrusive forms are:
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