HYDERABAD: Seismologists of National Geophysical Research Institute (NGRI) allayed fears that the massive earthquake that rocked North India measuring 7.6 on the Richter Scale could trigger after shocks in South India.

It is hardly surprising that an earthquake should occur in the Himalayan front, as it is a seismically active zone, says NGRI seismologist, Purnachandra Rao.

The epicentre of earthquake located 95 km north east of Pakistan capital Islamabad comes under the Himalayan front and is a result of the collision between the Eurasian plate and the Indian plate.

The earth surface is covered with plates, and these plates are constantly in motion. Whenever two plates collide, there is likely to be pressure resulting in seismic activity, he says.

Possibilities

Dr. Rao rejected the possibilities of an earthquake in South India in the wake of this earthquake citing no earthquake triggers aftershocks greater in magnitude than its own. Magnitude is the amount of energy released during the earthquake.

It is very rarely that earthquakes of the same magnitude occur in quick succession to each other. In this regard, he said the earthquake in Indonesia that happened hours after the earthquake in Pakistan on Saturday were not related to each other.

Zonation map

The earthquake in Sumatra which was followed by another earthquake within three months, was however a rare instance of earthquakes occurring in quick succession.

The Bureau of Indian Standards in New Delhi, which prepares the seismic zonation map of India, has placed Andhra Pradesh in Zone II and III. Zone V indicates that the areas falling under it are highly prone to earthquakes. Zone II and Zone III are relatively safer zones, Dr. Rao said.

Though there have been many earthquakes, Andhra Pradesh has seen only three big earthquakes where the magnitude exceeded 5 on the Richter Scale, namely in Vizianagaram, Ongole and Bhadrachalam. Hyderabad itself is pretty safe because it is away from the East coast belt and the Godavari valley, which are seismically prone.

Energy release

It is not just a matter of few points: for instance, the earthquake in Sumatra on December 26 that caused the tsunami, measured 9.3 as against the 7.6 that was recorded on Saturday.

But the energy released by the Dec. 26 earthquake was equal to 23,000 Nagasaki bombs, says Dr. Rao.

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