Earthquakes are distributed unevenly on the globe. In certain places they are more frequent and intense whereas in other places they are extremely rare and feeble or their effect is hardly perceptible. Studies on the occurrence of earthquakes on the globe have indicated that there are certain zones within the continents along which seismic shocks are felt rather frequently.
It has been observed that most of the destructive earthquakes originate within two well-defined zones or belts namely (i) The Circum-Pacific Belt and (ii) The Mediterranean-Himalayan Seismic belt.
(i) The Circum-Pacific Belt :
The Circum-Pacific Belt which encircles the rim of the Pacific ocean, has the maximum concentration of earthquakes. About 80 percent of all the terresterial earthquakes is concentrated in this belt. This ring coincides with the Circum Pacific Ring of Fire. This belt follows the western highlands of South and North America from Cape Horn to Alaska, crosses to Asia and extends southward along the eastern coast and related island arcs, and loops far to the south east and south beyond New Zealand.
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(ii) The Mediterranean-Himalayan belt :
The Mediterranean-Himalayan Seismic belt runs from Gibraltar to the East via the Atlas mountains, the Pyrenees, the Apennines, the Balkan mountains, the mountain chains of Asia Minor, the Caucasus, Hindu- kush, the Himalayas, the mountain chains of Burma and the islands of Indonesia, where it meets the Circum-Pacific belt in the north of Australia.
Apart from the above two belts, a number of shallow-focus earthquakes also occur in the zones of mid-oceanic ridges as well as in the body of the volcano or in its peripheral parts during eruption.
It is noticed that the present earthquake regions arc associated with the younger fold-mountain regions and the present earthquake activity is a phase of the end of the Alpine-Orogeny.