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  Plate Tectonics

Epicenters of major earthquakes of  the past, for which location data are available, are confined to certain narrow belts on the Earth’s surface. The circum-pacific belt is very prominent for major earthquake occurrences. The theory of Plate Tectonics has been developed to explain the geological features observed on the Earth’s surface. These include earthquake occurrences, formation and evolution of mountain chains and island arcs, regeneration of the ocean floor, locations of ridges and trenches (oceanic highs and ocean deeps), the present positions of the continents and other related issues. According to this theory the upper portion of the Earth, including the crust and the upper most uppermantle is in a mobile state with respect to the lower portion of the Earth     (Asthenosphere).

  Components of Plate Tectonics[1]

Relative movements between different parts of the Earth’s crust, called plates, over the asthenosphere occur along plate boundaries. Major earthquakes also occur along plate boundaries. These are called inter-plate earthquakes, and are more severe than those occurring in the plate interiors ( intra-plate earthquakes).

It has also been found that newer and newer material being added to the surface of the Earth under the oceans. The age of the surface material increases as one goes away from the oceanic ridges. It has been postulated, on the basis of this newer material found near the ocean ridges, that Earth’s material rises beneath the ridges due to mantle convection and reaches the Earth’s surface, where it spreads and cools down as it moves away from the ridge axis. On the surface the Earth’s material is consumed in trenches, where one plate goes beneath the other. Island arcs are formed where plates pass one another. Mountains are formed, and rise, as a result of collision between plates. The plates have also carried the various landmasses to their present positions, from where they are still continuously moving at an average speed of about 5 cm/year. The phenomenon of the movements of continents with respect to one another is called continental drift.

 This page was updated on 12 Jan 2011