Big earthquakes are naturally occurring events well outside the powers of humans to create or stop. An earthquake is caused by a sudden slip on a fault. Stresses in the earths outer layer push the side of the fault together. The friction across the surface of the fault holds the rocks together so they do not slip immediately when pushed sideways. Eventually enough stress builds up and the rocks slip suddenly, releasing energy in waves that travel through the rock to cause the shaking that we feel during an earthquake. Earthquakes typically originate several tens of miles below the surface of the earth. It takes many years decades to centuries to build up enough stress to make a large earthquake, and the fault may be tens to hundreds of miles long. The scale and force necessary to produce earthquakes are well beyond our daily lives. Likewise, people cannot prevent earthquakes from happening or stop them once theyve started giant nuclear explosions at shallow depths, like those in some movies, wont actually stop an earthquake.
The two most important variables affecting earthquake damage are the intensity of ground shaking cased by the quake and the quality of the engineering of structures in the region. The level of shaking, in turn, is controlled by the proximity of the earthquake source to the affected region and the types of rocks that seismic waves pass through en route (particularly those at or near the ground surface). Generally, the bigger and closer the earthquake, the stronger the shaking.
But there have been large earthquakes with very little damage either because they caused little shaking or because the buildings were built to withstand that shaking. In other cases, moderate earthquakes have caused significant damage either because the shaking was locally amplified or more likely because the structures were poorly engineered.
The word fault means?
Comments