An earthquake is caused by a sudden fault. Stresses in the earth's outer layer push the sides of a fault together. Stress builds up and the rock slips suddenly, releasing energy in the waves that travel through the rock to cause the shaking that we feel during an earthquake. An earthquake is caused by the release of stored elastic strain of energy during the rapid sliding along of a fault. The sliding will start at some location and progress away from the epicenter in each direction along the fault surface. At earth's surface, earthquakes manifest themselves by shaking and sometimes displacing the ground.
When large earthquakes epicenter is located of shore, the seabed sometimes suffers sufficient displacement to cause a tsunami. The shaking can also trigger landslides can occasionally volcanic activity. Tectonic earthquakes will occur anywhere within the earth where their is enough energy stored elastic strain energy to fracture propagation alone a fault plane. In case of a transform or convergent type plate boundaries, which forms the largest fault surfaces on earth. There are three main types of faults there is the normal, reverse, and strike-slip.
As you can see normal faults is when the right side of it falls they occur in a divergent boundary. A reverse (thrust) is when the right side goes up they are located on the convergent boundary. The Third one strike-slip fault the slide past each other this occur in the transform boundary. Where plate boundaries occur within continental lithosphere, deformation is speak out over a much larger area than the plate boundary itself. In the case of the San Andreas fault continental transform, many earthquakes occur away from the plate boundary and are related to strains developed within such a zone.
Another example is the strongly oblique convergent plate boundary trace. The Northridge earthquake was associated with movement on a blind thrust within such a zone. Another example is the strongly oblique convergent plate boundary between the Arabian and Eurasian plates where it runs through the northwestern part of the Zagros mountains. The deformation associated with this plate boundary is partitioned into nearly pure thrust sense movements perpendicular to the boundary over a wide zone to the southwest and nearly pure strike-slip motion along the Main Recent Fault close to the actual plate boundary itself. This is demonstrated by earthquake focal mechanisms.
All tectonic plates have internal stress fields caused by their interactions with neighbouring plates and sedimentary loading or unloading.
These stresses may be sufficient to cause failure along existing fault planes, giving rise to intraplate earthquakes. Why do earthquakes exist? why do we not know more about how to stop them from occurring? I truly don't know. What I do know is that they can cause alot of trouble.

The types of faults

The Fault line of an earthquake that ripped a street apart.

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