Earthquakes

Earthquakes are one of the most damaging natural disasters known to man. They have been known to destroy entire cities in their total time of 2 to 3 minutes. Most people do not know that earthquakes are common through out the entire world; they are just more powerful in places such as California and small countries in South America. The definition of earthquake is “ a series of vibrations induced in the earth's crust by the abrupt rupture and rebound of rocks in which elastic strain has been slowly accumulating” according to Infoseek.com.. As a consequence of continental plate movement, the Earth's surface near active faults deforms before, during and after earthquakes. Similarly, the ground surface near active volcanoes also deforms as a consequence of eruptions and volcano evolution. Crystal deformation can be observed as relative movement of points on the Earth's surface, ground tilt, ground strain, and fault slip (creep). There are five primary regions in California where continuing crustal deformation and associated seismicity indicate the most serious earthquake or volcanic hazard. Monitoring in these regions allows researchers to understand the source and characteristics of this hazard so they can attempt to minimize its effects. A fault is a fracture or zone of fractures between two blocks of rock. Faults allow the blocks to move relative to each other. This movement may occur rapidly, in the form of an earthquake - or may occur slowly, in the form of creep. Faults may range in length from a few millimeters to thousands of kilometers. Most faults produce repeated displacements over geologic time. During an earthquake, the rock on one side of the fault suddenly slips with respect to the other. The fault surface can be horizontal or vertical or some arbitrary angle in between. Earth scientists use the angle of the fault with respect to the surface (known as the dip) and the direction of slip along the fault to classify faults.