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  Earthquakes In India

            Earthquakes of different severity – small, moderate and the most destructive ones - have occurred in India during the past one hundred years. While some regions have experienced earthquakes more frequently than others, no part of the country can be considered earthquake free. Earthquakes have occurred in the northern and the northeastern regions more frequently. These have been less frequent in the central and the peninsular regions. For not very sound reasons, a widespread belief developed that peninsular India was seismically stable, and earthquake free. The earthquake on December 10, 1967 in the Koyna region of western Maharashtra was attributed to the reservoir, and was classified as an induced earthquake. Since earthquakes have followed impoundment of reservoirs in some parts of the world, this explanation helped keeping the stability view. Occurrences of the Latur earthquake of September 30, 1993, which killed over ten thousand persons and the Jabalpur earthquake of May 21, 1997 now make one to suspect that earthquakes could occur anywhere in the peninsular region (these will, of course, be confined to geological faults). A reservoir also, after all, can only hasten the release of the accumulated strain energy. Accumulation of the energy cannot be attributed to the reservoir. Earth scientists believe, in the framework of plate tectonics, that the Indian plate is drifting northwards, at a rate of as much as 5 cm/year, colliding with the Eurasian plate. This collision is considered responsible for the rise of the Himalayas, the strong earthquakes near the plate boundary and small to moderate size earthquakes in interiors of the plate. Major Indian earthquakes, beginning from the Kutch earthquake of 1819 are listed in the Table-1 given below. Epicenteral locations and magnitudes of over  ten thousand earthquakes are listed  in the recorded history of the earthquakes for the past four hunderd years. It may, however, be noted that until as early as the 1960s only strong earthquakes which had produced damaging effects on the ground were catalogued. It was only after the installation of sensitive seismic instruments in different parts of the country that earthquakes of small magnitudes (down to 4.5) were catalogued. Earthquake data in India are collected  and catalogued by the India Meteorological Department (IMD). They operate over  two  hundred  observatories nationwide (Though all these are not of the same quality). Several seismic observatories are operated by managements of some  river valley projects. A seismological array consisting of twenty seismometers spread over a 20 kmx 20 km area in southern India is operated by the Bhabba Atomic Research Centre. An independent seismological Observatory is being operated by the National Geophysical Research Institute (NGRI) at Hyderabad in Andhra Pradesh. Networks have also been installed in the Koyna and the north east regions to investigate regional seismicity of these areas.

Table-1: Major Known Indian Earthquakes.