Monday, April 27, 2015

About Earthquakes

What is an earthquake?
The Earth's structure has three parts — an outer silicate solid crust (till about 30km from the surface), a viscous mantle (2,900km thick) below the crust and a core (3,500km diameter) at the center. The uppermost part of the mantle and the crust is broken into seven major tectonic plates — African, Australian, Eurasian, North American, South American, and Pacific. The motion of these plates against each other causes earthquakes.
How is an earthquake measured?
Energy in the form of seismic waves is released after an earthquake and seismometers measure its amplitude to calculate the quake's intensity. For a long time, earthquakes were measured on the Richter scale. Since the scale was based on conditions in California and was not reliable in measuring large earthquakes, it was replaced by a 'moment magnitude' scale in the 1970s.
Why is the Himalayan region more prone to earthquakes?
The Indian plate, which is part of the Indo-Australian plate, is moving in a north-north-east direction and colliding with the Eurasian plate. The Himalayas came up as a result of this movement. The collision has resulted in the formation of many fault lines along the region, which has made it highly susceptible to earthquakes.
Which regions of earth are most susceptible to earthquakes?
The Pacific 'Ring of Fire', a horseshoe shaped region encircling the Pacific Ocean, accounts for 90% of all earthquakes. This 40,000 km long stretch has 452 volcanoes and is home to over 75% of the world's volcanoes. The next most active region is the Alpide belt, which lies along Java, Sumatra, the Himalayas, the Mediterranean, and the Atlantic Ocean.

What are the various seismic zones in India?
According to the Indian metrological department, the Bureau of Indian Standards has grouped the country into four seismic zones, from Zone V, the most active, to Zone II, the least active. Zone V consists of parts of Jammu and Kashmir, Himachal Pradesh, Uttarakhand, Rann of Kutch, part of north Bihar and the Andaman & Nicobar Islands. The remaining parts of Jammu & Kashmir and Himachal Pradesh, Delhi, Sikkim, northern Uttar Pradesh, Bihar and West Bengal, parts of Gujarat and small portions of Maharashtra near the west coast and Rajasthan fall under zone IV (severe intensity zone).


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