Tuesday, August 10, 2010

Seismic clues and Earth quakes

Earthquake Zones INDIA
Earth quakes produce shock waves that reverberate outwards through rock from a central point of energy release. Different kinds of waves can be identified and their paths can be plotted. Rayleigh waves and love waves only travel around the surface of the Earth. Primary waves and Secondary waves travel through the Earth, although Secondary waves cannot cross the boundary of the molten outer core. They reflected off that boundary, thus revealing deep structure. Waves picked up hundreds of receivers are used to build up a structural cross section.
The continents slowly slip past one another, raising, falling, straining and distorting as they go. Their passage is seldom smooth. With little lubrication, stain builds up until the rock can withstand it no longer and the ground cracks. The resulting earthquake can release tremendous amounts of energy in the form of seismic waves that run through the ground, shaking buildings with a destructive force. Movements 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 waves in deep water, but the waves travel up to 800Km/ hour. They slowdown in shallow water but their amplitude increases so that they reach heights of up to 160fts.  These tidal waves , or tsunamis, wreak great havoc on coastal areas.