March 29, 2005
India Daily

Scientists are scratching their heads to find out the reasons for the increasing amounts of earthquakes under the oceans specially the two mega quakes off the coast of Sumatra.

According to a theory called Wadati-Benioff zones, or simply Benioff zones earthquakes tend to be concentrated in certain areas, most notably along the oceanic trenches and spreading ridges. The prominent underwater earthquake zones parallel to the trenches that typically were inclined 40-60° from the horizontal and extended several hundred kilometers into the Earth.

Geologists believe that the ocean floor and underwater portion of the earth’s crust are continuously getting recycled. In certain areas, the magma is expanding, creating new ridges and therefore older ridges are moving apart. Based on this, do not assume that earth is expanding. In certain areas under the ocean, the magma is actually receding. When magma recedes, that part of the world experiences less stress and the porous crust can accumulate fossil oil and gas. Eventually as the magma recedes further, the ocean floor collapses into the magma. On another side of the world thousands of miles away, new ridges are formed and magma comes out to support the theory of expanding or shifting-apart ocean floors. Many Geologists believe, under ocean fault lines are caused by this phenomenon at any instance of time.

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