Monday, August 23, 2010

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).