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Why earthquakes occur

Why do earthquakes occur? And cause such havoc? The sudden release of energy does it, we are told. What form of energy is this, and why is it suddenly released?

india Updated: Mar 14, 2003 11:58 IST
PTI

Why do earthquakes occur? The sudden release of energy does it, we are told. What form of energy is this, and why is it suddenly released?

The form of energy most commonly involved is the release of elastic strain energy. Though other forms of energy are also involved, eg gravitational potential, chemical reactions, or motion of bodies, elastic strain within the crust of the Earth is the only form of energy that is stored in sufficient quantity in the Earth to produce major earthquakes. As these happen within the earth’s crust, these are called tectonic quakes (from the Greek tektonikos – of a builder). Most seismologists agree with the theory of plate tectonics, which explains the process.

Plates move in relation to each other. However, this movement is not always similar. They can move towards each other, away from each other and also slide past each other. While the moving away of plates or sliding past each other does not cause stress to be accumulated, converging plates are the danger zone. This is because as they crash against each other and one subducts below the other, enormous pressure gets built up in the rock layers.

When earthquakes occur at the boundary of plates, they are called Interplate Earthquakes. Examples of these would include those in the Himalayan region, or the Pacific quakes. Those that occur away from plate boundaries are called Intraplate earthquakes.

Those that occur in the supposedly stable parts, also usually the oldest parts, of the continental crust are called Stable Continental Region Earthquakes. The Latur earthquake would fall in this category.

If you’ve felt a major quake, you would have noticed that there are vibrations even after the main quake. An earthquake, especially a major one, is rarely a single movement. Instead the main quake is followed, and occasionally even preceded by a series of smaller quakes. As in the case of the Bhuj quake, these aftershocks may felt up to even days after the main quake.