■ HOW ARE EARTHQUAKE WAVES PRODUCED ?
◇ The abrupt release of energy along a fault (sharp break in the crustal layer) causes earthquake waves. Rock layers along a fault tend to move in opposite directions due to the force excreted on them but are held in place by counteracting frictional force exerted by the overlying rock strata.
◇ The pressure on the rock layers builds up over a period and overcomes the frictional force resulting in a sudden movement generating shockwaves (seismic waves) that travel in all directions.
◇ The point where the energy is released is called the focus or the hypocentre of an earthquake. The point on the surface directly above the focus is called epicentre. An instrument called ‘seismograph’ records the waves reaching the surface.
