Earthquakeon June 19, 2009 at 3:25 pm
An earthquake is caused by a sudden slip on a fault. The tectonic plates are always slowly moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the earth’s crust and cause the shaking that we feel.
In California there are two plates- the Pacific Plate and the North American Plate. The Pacific Plate consists of most of the Pacific Ocean floor and the California Coast line. The North American Plate comprises most the North American Continent and parts of the Atlantic Ocean floor. The primary boundary between these two plates is the San Andreas Fault. The San Andreas Fault is more than 650 miles long and extends to depths of at least 10 miles. Many other smaller faults like the Hayward (Northern California) and the San Jacinto (Southern California) branch from and join the San Andreas Fault Zone. The Pacific Plate grinds northwestward past the North American Plate at a rate of about two inches per year.
Parts of the San Andreas Fault system adapt to this movement by constant “creep” resulting in many tiny shocks and a few moderate earth tremors. In other areas where creep is not
Damaged caused by earthquake
The effects of an earthquake are strongest in a broad zone covering the epicenter. The Surface of the ground cracking associated with fault that reach the surface often occurs, with horizontal and vertical displacement of a number of yards common. Such progress does not have to occur during a major earthquake, slight interrupted movements called fault creep can be accompanied by micro earthquakes too little to be felt. The level of earthquake vibration and subsequent damage to a region is partly dependent on the ground. For (eg) earthquake vibrations last longer and are of greater wave amplitudes in unconsolidated outside material, such as poorly compacted fill or river deposits, bedrock areas get fewer property. The worst damage occurs in more populated urban area where structures are not built to withstand passionate shaking. There, L waves can produce critical vibrations in buildings and break water and gas lines, starting uncontrollable fires.
Damage and loss of life sustained for the stage of an earthquake result from falling structures and flying glass and objects. Flexible structure built on bedrock are normally more resistant to earthquake damage than rigid structure built on loose soil. In some areas, an earthquake can trigger mudslides, which slip down mountain slopes and can put in the ground habitations below. The submarine earthquake can produce a tsunami, a series of damaging waves that ripple outward from the earthquake epicenter and inundate coastal cities.