Elastic rebound theory

Earthquake belts in the world

Circum-Pacific belt: This follows the region around the Pacific Ocean from Japan, China, Alaska Aleutians, California (San Andreas fault system),

Mexico, Equador, Peru, Chile and New Zealand. These are the areas characterized by plate subduction, active volcanoes, strain build-up and periodic release, causing earthquakes.

•         Mid-Atlantic Ridge: This follows the lines of Mid-Oceanic Ridges from near the North Pole to the equator, turning around South Africa and ends up to Rift Valley region of East Africa. Seismicity is low in this region.

•         The Alpine-Himalayan Trans-Asiatic Belt: The Alpine mountain areas of Europe, North Africa, Asia Minor, Caucasus, Turkey, Iraq, Iran, Himalayan region such as Kashmir to Assam, Myanmar and Philippines. This zone passes through boundaries of continental crustal plate with high mountain ranges where intense compression takes place.

Elastic rebound theory

Each type of plate intersection produces significant straining in crustal rocks. The strain is accumulated by gradual shifting of tectonic plates. The rocks become disturbed but maintain their original positions because of continuity, mechanical bond and friction. When accumulated stress finally exceeds the strength of rocks, fracture occurs and the Earth shapes back in to an unstrained position. This phenomenon is generally known as ‘elastic rebound theory’ or Reid’s theory. The great release of energy associated with the rupture of rocks produces shock waves that propagate through Earth’s crust and cause an earthquake. The great (major) earthquakes are usually the transform fault and subduction types. Sometimes, earthquakes are associated with volcanic eruptions or subterranean movement of magma.