Earthquakes are tremors which are produced by the passage of
vibratory waves through the rocks of the earth. If you throw a stone in a pound
of still water, a series of concentric waves are produced on the surface of
water. These waves spread out in all directions from the point where the stone
strikes the water. Similarly, any sudden disturbances in the earth’s crust may
produce vibrations in the crust which travels in all directions from the point
of disturbance.
Earthquakes and volcanoes are endogenic forces while
weathering and agents of sculpture are exogenic forces. Some are sudden forces
and bring about sudden changes. Earthquakes and volcanoes are examples of
sudden forces. There are other forces which work slowly and take longer
duration of time to show their effects.