Earthquake, any sudden shaking of the ground caused by the passage of seismic waves through Earths’s rocks. Seismic waves are produce when some form of energy stored in Earth’s crust is suddenly released, usually when masses of rock straining against one another suddenly fracture and “slip.” Earthquakes occur most often along geologic faults, narrow zones where rock masses move in relation to one another
- A tectonic earthquake is one that occurs when the earth’s crust breaks due to geological forces on rocks and adjoining plates that cause physical and chemical changes.
- A volcanic earthquake is any earthquake that results from tectonic forces which occur in conjunction with volcanic activity.
- A collapse earthquake are small earthquakes in underground caverns and mines that are caused by seismic waves produced from the explosion of rock on the surface.
- An explosion earthquake is an earthquake that is the result of the detonation of a nuclear and/or chemical device.
Seismic waves is of three types-primary waves,secondary waves and surface wave.
Of the body waves, the primary waves has the higher speed of propagation and so reaches a seismic recording station faster than the secondary, or S, wave. P waves, also called compressional or longitudinal waves, give the transmitting medium whether liquid, solid, or gas a back-and-forth motion in the direction of the path of propagation, thus stretching or compressing the medium as the wave passes any one point in a manner similar to that of sound waves in air.
P waves can travel in all three medius.S waves can only travel in solid medium.
Earthquakes can occur due to human activity or natural reason like volcano,tsunami etc.