Insights Static Quiz -121, 2018 –Physical Geography and Environment

Answer – a

• An earthquake in simple words is shaking of the earth. It is a natural event. It is caused due to release of energy, which generates waves that travel in all directions.
• The release of energy occurs along a fault. A fault is a sharp break in the crustal rocks. Rocks along a fault tend to move in opposite directions. As the overlying rock strata press them, the friction locks them together. However, their tendency to move apart at some point of time overcomes the friction. As a result, the blocks get deformed and eventually, they slide past one another abruptly. This causes a release of energy, and the energy waves travel in all directions.

Answer – A

All natural earthquakes take place in the Lithosphere where  lithosphere refers to the portion of depth up to 200 km from the surface of the earth.

Answer – A

• Earthquake waves are basically of two types — body waves and surface waves.
• Body waves are generated due to the release of energy at the focus and move in all directions travelling through the body of the earth. The body waves interact with the surface rocks and generate new set of waves called surface waves. These waves move along the surface.
• The velocity of waves changes as they travel through materials with different densities. The denser the material, the higher is the velocity. Their direction also changes as they reflect or refract when coming across materials with different densities

Answer – D

There are two types of body waves. They are called P and S-waves.

• P-waves move faster and are the first to arrive at the surface. These are also called ‘primary waves’. S-waves arrive at the surface with some time lag. These are called secondary waves.
• 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.
• 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 thus considered to be the most damaging waves.

Answer – c

• The point where the energy is released is called the focus of an earthquake, alternatively, it is called the hypocentre. The energy waves travelling in different directions reach the surface.
• The point on the surface, nearest to the focus, is called epicentre. It is the first one to experience the waves. It is a point directly above the focus.