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High Resolution 1:10,000 scale Mapping Strategy of Multi ... - NDMA

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earthquakes <strong>of</strong> magnitude 5.0 and above have been plotted for last <strong>10</strong>0 years (1905<br />

to 2006) in India and neighborhood, which clearly depict the seismicity <strong>of</strong> India. The<br />

clear feature <strong>of</strong> the seismicity plot is the earthquake events are mainly distributed<br />

along with the plate boundary and Kutch. However, the devastating intra plate<br />

earthquake <strong>of</strong> magnitude 6 and above are also seen to be occurring over main land<br />

along with active seismotectonics faults making more than 50% <strong>of</strong> the land area<br />

earthquake hazard prone.<br />

CHARACTERISTICS AND EFFECTS OF EARTHQUAKES<br />

Earthquake swarms<br />

Earthquake swarms also occur frequently over land mass. These are low intensity<br />

(around 3 magnitude) series <strong>of</strong> earthquakes occurring at the location. The frequency<br />

<strong>of</strong> tremors could be as high <strong>of</strong> 50 shocks a day. These are normally originated from<br />

shallow depth. The Maharashtra (Nanded 2006-08), Haryana (Jind 2003) and<br />

Gujarat (Bhavnagar-2<strong>000</strong>) are typical examples. These swarms cause damage to<br />

hutments and even cracks in RCC structures.<br />

Aftershocks<br />

An aftershock is an earthquake that occurs after a previous earthquake, the main<br />

shock. An aftershock is in the same region <strong>of</strong> the main shock but always <strong>of</strong> a smaller<br />

magnitude. If an aftershock is larger than the main shock, the aftershock is<br />

redesignated as the main shock and the original main shock is redesignated as a<br />

foreshock. Aftershocks are formed as the crust around the displaced fault plane<br />

adjusts to the effects <strong>of</strong> the main shock. Large numbers <strong>of</strong> aftershocks have been<br />

recorded by IMD after each earthquake magnitude 6 and above viz Bhuj, Uttar<br />

Kashi, Chamoli, Jabalapur etc. Some time aftershocks cause significant loss <strong>of</strong> life<br />

and property and Latur earthquake is a typical example in India. The aftershock <strong>of</strong><br />

Bhuj earthquake has caused lot <strong>of</strong> damage to property.<br />

Indian subcontinent has a history <strong>of</strong> devastating earthquakes. The major reason for<br />

the high frequency and intensity <strong>of</strong> the earthquakes is that the Indian plate is driving<br />

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