by Sabeen Sidiki

Created on: November 04, 2008   Last Updated: November 15, 2008

Earthquakes result from the strain caused by the movement of the plates that make up the earth's outer shell; earthquakes are directly associated with the activities that occur at ocean ridges, trenches, etc. What happens is that when the earth's surface cannot cope with the strain it breaks up and releases tremendous amounts of energy in the form of sudden violent shocks.

Earthquakes cause fissures in the ground; also, landslides and avalanches are triggered off; sometimes the courses of rivers are diverted. An earthquake causes destruction all round; it can wipe out an entire community in minutes. Coastal earthquakes generate giant waves which can cause destruction thousands of miles away. The loss of lives and destruction of property that occured in Armenia in Soviet Russia were unimaginably high and point to the magnitude of the devastating effects of earthquakes.

The point at which an earthquake occurs is called the focus or hypocentre. According to seismologists - scientists who study earthquakes - there are three types of earthquakes. Earthquakes are classified on the basis of the focus below the earth's surface. The three types of earthquakes are shallow earthquakes, intermediate ones, and deep ones. Shallow earthquakes take place at depths of zero to seventy km, intermediate ones at the depth of 70- 300 km, and deep earthquakes below 300 km. It is the shallow earthquakes which cause most of the damage at the earth's surface. There are about three times as many intermediate shocks as the deep ones, and about ten times as many as shallow ones. The deepest earthquake known to have caused damage was the one in Romania in 1940, it killed about a thousand people. Its focus was about 160 km deep.

The point on the surface of the earth directly above the focus is called the epicentre. Earthquake epicentres are largely concentrated in narrow belts which coincide with the boundaries of the earth's plates. The most intense earthquake activity is round the margin of the Pacific. About 75% of all shallow earthquakes, 90% of intermediate earthquakes, and almost all deep earthquakes take place in this belt. It covers the west coast of South America, the west coast of North America, the Caribbean, parts of Asia, Indonesia, New Zealand and the Antarctic . There is yet another belt which spreads through the Alps and North Africa, along the northern shores of the Mediterranean, eastwards through Iran and the Himalayas, then through southern China to join the Pacific belt.

Earthquakes

• 1
• 2
• Next Page >>