Solution:

An earthquake is a sudden, rapid shaking of the earth surface caused by the breaking and shifting of rocks beneath.

During earthquake, ground motion occurs in a random fashion in all directions radiating from a point within earth crust, called epicentre.

It causes vibrations of structures and induce inertia forces on them. As a result, structure may collapse resulting into loss of property and lives.

Earthquakes do not kill people, vulnerable buildings do so. Hence there is need of designing earthquake resistant buildings, especially in the earthquake prone areas.

Depending upon the possible causes,

The earthquakes may be classified as:

(i). Natural earthquake.

(ii). Earthquakes due to induced activities.

(i). Natural earthquake:

Natural earthquakes may be due to

(i) active faults

(ii) movement of tectonic plates or

(iii) due to volcanic eruptions.

In earth’s crust there are some faults which are not yet settled. The displacement of rocks along faults cause earthquake.

Tectonic means large scale process affecting the structure of the earth crust. This process causes gradual movement of material within the crust of earth.

Sometimes it shakes the earth crust. Volcano is a mountain or hill having a crater through which lava, rock fragments, hot vapour and gas are or have been erupted from the earth’s crust.

Occasionally the volcanoes become active and create earthquake near the mountain crater.

(ii) Earthquakes due to Induced Activities:

Another quarter were caused by loading the Earth’s surface where it was not loaded before, such as reservoirs held behind dams, which can add stress to faults.

The last quarter happen when fluids produced from the Earth are injected back into it, like in a disposal well, where wastewater from oil or gas production changes the pressure conditions, sometimes causing the fault to slip.

We measure stress in the crust with wells drilled deep into the earth for energy resources or research. A delicate balance exists between rock strength, fluid pressure, and the direction and magnitude of stress in the earth at any given time.

It is sometimes possible for fluid injection or mining activities to upset this balance and trigger earthquakes on faults that might not move in a naturally occurring earthquake for thousands of years.

These are caused by vibrations induced by atomic explosions and collapse of ground due to faulty mining.