Earthquake
An earthquake is the sudden , sometimes violent movement of the earths surface from the release of energy in the earth’s crust. An earthquake happens when two blocks of the earth suddenly slip past one another. The surface where they slip is called the fault or fault plane. The location below the earth’s surface where the earthquake starts is called the hypocenter (focus), and the location directly above it on the surface of the earth is called the epicenter.
There are many different types of earthquakes: tectonic, volcanic, and explosion. The type of earthquake depends on the region where it occurs and the geological make-up of that region. The most common are tectonic earthquakes. These occur when rocks in the earth's crust break due to geological forces created by movement of tectonic plates. Another type ,volcanic earthquakes, occur in conjunction with volcanic activity. Collapse earthquakes are small earthquakes in underground caverns and mines, and explosion earthquakes result from the explosion of nuclear and chemical devices. We can measure motion from large tectonic earthquakes using GPS because rocks on either side of a fault are offset during this type of earthquake
Earthquakes occurs both along plate edges and along faults .Earthquakes occurs principally in two elongated regions .One passes around the pacific ocean (Circum –Pacific Belt) and includes New Zealand ,New Guinea ,Japan ,Alaska ,the Aleutian Islands and the west coasts of North and South America .The othe region underlies the Mediterranean region eastward through Asia ,passing under the Atlas ,Alpine ,Iranian ,Himalayan and Burmese Mountains ,the island chains of Indonesia and new Guinea ,the Solomon Island ,and the New Hebrides .A less active region consists of Mid-Oceanic Ridges including the sub marine mountains underlying the center of the Atlantic, Indian and South Pacific Oceans.
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