- Earthquakes are sudden, violent shaking or vibration of the earth crust produced by the shock waves resulting mainly from a sudden displacement along a fault.
Why does it happen?
Earthquakes are associated with all types of plate boundaries. Earthquakes occur when tension is released from inside the Earth. Plates do not always move smoothly alongside each other and may get stuck. When this happens pressure starts to build up. When the accumulated pressure (energy) is eventually or abruptly released, earthquake tends to occur. While the fault rupture can be visible at the surface, the actual displacement may occur at a considerable depth as deep as 500 km beneath the surface in case of a subduction zone. Earthquake may also develop from the movement of magma or due to sudden ground subsidence.
Quasi-natural earthquakes: Man made causes like nuclear testing, building of large dam or reservoir, oil drilling, coal mining may also cause earthquakes.
Focus or hypocenter: The place beneath the ground where the earthquake originates is called the focus. It is also the center of the fault motion where energy is released; originating different kinds of seismic waves.
Epicenter: The point on the Earth’s surface directly above the focus is called the epicenter. The strongest shocks and crustal vibration are often felt on at the epicenter.
Aftershock: These are the series of small earthquake that follow a major earthquake near the original earth movement. If the initial earthquake is strong, then the aftershocks can also be very strong. Aftershocks represent the redistribution of stress on the fault zone.