What Is An Earthquake And What Is The Cause Of An Earthquake?

Simply stated, an earthquake is a shaking or quaking of the earth. There have been numerous conjectures about their causes. Ancient Japanese mythology blamed the movement of a spider that carried the earth on its back. Mongolians anciently attributed earthquakes to the unsteady support of a giant hog.
Even in comparatively recent times scientific theories as to their cause have come and gone. Today, earthquakes are believed to result from a sudden dislocation in the earth's crust. But one view gaining wider acceptance is that the earth's crust is not rigid, but is made up of a series of "plates" that move over the earth's "mantle."
According to this view, when these "plates" (which are several miles thick) collide, one slides under the other, bending rocks in the process. In other cases, the horizontal action of these "plates" passing one another exerts tremendous pressure on crystal rock. Such movements occur along a "fault" or fracture in the earth's surface. Then, it is believed, when the crust can no longer tolerate the strain, it "snaps" into a new position.

The Earth's Lithosphere is divided into 15 major Tectonic Plates of various sizes. These plates float on the partially molten Astheno sphere below, and it is because they are floating that they have the freedom to move horizontally. The theory of plate tectonics assumes that each plate behaves as a rigid unit, deforming only at its edge. The edges, or margins can diverse, converge or slide past one another. But there is a very little change anywhere in the middle of a plate. Actually some of the Earth's most dynamic features, such as volcanoes and earthquakes define the boundaries of the main plates.

The cause of the Earthquake is, when plate boundaries are the most tectonically active parts of the Earth, they are where most mountain building, Earthquakes and volcanoes occur. An Earthquake occurs when the edges of two plates suddenly slide past each other along a fault line. The severity of an earthquake is measured on the Richter scale. It is logarithmic, so each additional point represents a tenfold increase in severity. The key to plate tectonic is that the surface of the earth exists in a state of equilibrium and it provides a global frame work that successfully explains many of the structural and geophysical phenomenon a on the earth's surface ranging from mountain building and earth quakes to continental drift. Even though the mechanics of earthquakes are understood, accurate prediction of their occurrence has remained beyond reach.

Earthquake is sudden releases of energy which results into ground shaking or vibrations of the ground. When energy stored in the earth releases as a result of certain kind of stresses and strain effects, it results into an Earthquake. The earth quake is generated by waves. When two blocks of rocks on both sides of fault slip suddenly resulting into vibrations.

Normally earthquake occurs at the plate boundaries, which is the region of the earth crust or upper mantle boundary where the most breakage take place. Whenever there is slippage if block at the time of earthquake suddenly resulting into intense kind of vibration known as seismic waves (from Greek word seismic meaning shock or earthquake).the energy waves travel from the focus point of the earth just like as ripple marks produced on the surface of water.

If it is near epicenter, it result into more sever land and ground shaking. According to seismologist report almost 1 million small earth quakes are detected whereas large earthquake occurs once after few years.

In the last 500 years, millions of people have been killed by earthquake throughout the world. Earthquake affect the land, damage to the property, buildings create tsunami. Study of earthquakes is known as Seismology and person who studies that subject is known as Seismologist.

The crust of the earth is made of plates which are constantly moving. Some of these plates have faults which fracture, and the plates collide causing an earthquake.