Question

The point of origin of waves of earthquakes is called _______________.
A. Seismic Focus
B. Seismic line
C. Seismic centre
D. None of these

Answer 1

Hint:
> Earthquakes are waves of energy that move rapidly outwards from the point of origin.
> The points of origin are always in the interior of the earth.
> The points of origin should not be confused with the epicentre of an earthquake.

Complete answer:
Earthquakes are instances when the surface of the earth shakes due to sudden release of a large amount of energy in the earth’s lithosphere. It is caused due to the released energy moving outwards in the form of waves of energy that disturb and dislocate the rocks in the lithosphere. The waves themselves are of many kinds, like the surface and body waves. The different points of origin and impact of these waves are known by different terms to make studying them easier. Let us now see what each of the terms mean-

A. Seismic focus is the place of origin of the energy waves within the interior of the earth. These are usually found on places which are on or around the fault lines of the tectonic plates. Thus, this is the correct option.

B. Seismic lines are narrow corridors created to deploy and transport equipment for geological survey. It is called seismic lines because the geophones present in these corridors pick up vibrations. It is not related to the place of origin of earthquake waves. Therefore, this option is incorrect.

C. Seismic centre is the point on the earth’s surface directly above the focus of an earthquake. Therefore, it is not the point where the waves originate; rather it is where the pint of origin is located directly underneath. Therefore, this is also not the correct answer.

D. Since the first option, Seismic Focus, is the correct answer, this is not the correct option.

Therefore, the correct answer is A

Note:
> The scale or magnitude of the earthquakes is measured in the Richter scale.
> The shallow focus earthquakes are more damaging and tend to be larger because of the higher strain of energy that the waves carry.
> There are three main earthquake belts on earth- The Circum-pacific belt (called the pacific ring of fire), the Oceanic Ridge belt and the Alpide belt.
> Seismic waves are divided into two types- the body waves (Primary and Secondary waves) and the surface waves (Love and Rayleigh waves)