Epicenter of Earthquake

Although displacement in an earthquake is usually along the plane of a fault, seismic waves appear to radiate out in all directions from a single point. The epicenter of a quake is the point on the ground directly above that focus, which is called the hypo center. The focus may be many kilometers deep within the Earth. Quakes on subduction crustal plates can occur at such a depth that the surrounding rock is more molten and therefore too soft to sustain a brittle fracture. These quakes happen when minerals suddenly change into a denser phase as a result of increases in temperature and pressure.

The San Andreas Fault in California is the most famous crack in the world. Since the great earthquake of 1906 in San Francisco, no one has doubted the fault’s destructive power, released as the pacific crustal plat e slides slowly north past the North American plate. In places the fault lines cross urban and industrial areas where earth quake activity could be potentially devastating.

Our knowledge of why earthquakes happen is a major step towards improved prediction. In 1992 a 7.4 magnitude earthquake in California was mapped by combining satellite radar images take before and after the shock. The closest contours around the fault show the zone of maximum ground displacement. Multiple faulting caused the confuse zone near the epicenter. Radar mapping is more accurate than field surveys, which require monitoring equipment to be set up before shock.

Earth Quakes & Earthquake Zones

The continents slowly slip past one another, rising, falling, straining and distorting as they go.  Their passage is seldom smooth.  With little lubrication, strain builds up until the rock can withstand it no longer and the cracks. The resulting earth quake can release tremendous amounts of energy in the form of seismic waves that run through the ground, shaking buildings with destructive force. Movement along the fracture or fault line can extend for many meters, and can occur horizontally and vertically. Seismic seabed movement can generate seemingly harmless waves in deep water, but the waves travel at u to 800 Km/h. they are slowed down in shallow water but their amplitude increases so that they reach height of 50 meters. These tidal waves, or tsunamis, wreak great havoc on coastal areas.

Most earthquakes, like volcanoes, take place in specific zones that correspond to the boundaries of tectonic plates. Shallow earthquakes happen where one plate moves against another on the surface, as in California, and where displacement is horizontal. Deeper earth quakes occur where one plate is sliding beneath another, described as subduction zone. This is happening along the west coast of South America, where the ocean crust dives beneath the continent. Volcanoes occur in the same regions, as magma is produced at both constructive (where crust is being generated) and destructive (where it is disappearing) margins. The most violent eruptions occur at destructive margins, and  are known as Andesite volcanoes (after the Andes mountains).