Economy

A massive quake, but with no big wave

M. Somasekhar Hyderabad | Updated on March 12, 2018 Published on April 11, 2012

The Marina Beach in Chennai wears a deserted look after a tsunami alert wasissued following a massive earthquake in the ocean south-west of Indonesia’s Aceh province on Wednesday. Tremors were felt in southern and eastern parts of the country sending panicked people racing into the streets. — K. Pichumani

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Today's earthquake occurred due to a ‘strike slip fault'. In this mechanism, two plates slide past each other in the earth's crust.

The earthquake of magnitude 8.6 that struck the coast of the Indonesian island of Sumatra on Wednesday afternoon was completely different from the killer 9.1 magnitude one of December 26, 2004.

While the 2004 earthquake triggered devastating tsunami waves, causing havoc across several countries including India, the present one luckily did not, because of this difference in fault mechanism, say earthquake experts from the National Geophysical Research Institute (NGRI) here,

Today's earthquake occurred due to a ‘strike slip fault'. In this mechanism, two plates slide past each other in the earth's crust. This resulted in the sea waters not being pushed with force in an upward direction.

Hence, the earthquake did not trigger major tsunami activity.

In the case of the 2004 earthquake, the high magnitude of 9.1 coincided with a vertical thrust movement of the two plates, forcing the water being displaced with force upwards, hence tsunami waves were generated, explained Mr R.K. Chadha, seismologist of NGRI.

Aftershocks

The reason why the INCOIS, the Indian Tsunami warning centre also gave a ‘watch' alert for tsunami was because of the observed mechanism of the present earthquake, he told Business Line.

The NGRI, a premier lab studying earthquakes in India, recorded the huge earthquake. It has also recorded 12 aftershocks so far.

The epicentre of the present earthquake is around 150-200 km of the earlier one, in the Sumatra-Java subduction zone. The region is highly active seismologically, with recordings of 4-5 tremors of magnitude 4 on a daily basis, he added.

The impact of such earthquakes can be felt along the coast up to 2500 km.

Hence, people feeling the shocks in Chennai, coastal Andhra Pradesh and Kolkata have been reported, Mr Chadha said.

Published on April 11, 2012
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