Sumatra shocker for state

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The two great earthquakes off the west coast of northern Sumatra were felt in the city and other parts of the country, including the east coast and Kerala on Wednesday.

While tsunami warning was issued in south India, the region escaped disaster due to the horizontal shifting of the tectonic plates. The maximum change in tides was experienced at Kambell Bay in Greater Nicobar, where the waves reached 45 cm.

“In all, there were four earthquakes off the coast of northern Sumatra on Wednesday. While the intensity of two was very high, the effects of aftershocks were also intense,” said Dr Y.E.A. Raj, deputy director general of meteorology, Regional Meteorological Centre.

“The first earthquake struck at 2.08 pm with an intensity of 8.5 on the Richter scale. The other major quake occurred at 4.13 pm and measured 8.1 on the Richter scale,” he added.

National Institute of Ocean Technology director, Dr M.A. Atmanand, noted that with the help of exact measurement of seismic chart, water levels and various gauges, it was found that there was no need to worry about tsunami in the Indian mainland. “The country felt sudden variation in tides only at Greater Nicobar,” he added.

The epicentre was 33 kilometres beneath the ocean floor, about 495 km southwest of Banda Aceh. The Pacific tsunami warning centre said a tsunami watch was in effect for the entire Indian Ocean and countries, including Thailand, Indonesia, Sri Lanka, Malaysia and India.

According to experts, tsunami did not follow the massive earthquakes due to the strike-slip mode of quakes. “Strike-slip earthquakes are completely horizontal and there is no vertical displacement.

A vertical uplift of water is needed to generate a tsunami and so this part of the world escaped another devastation like the 2004 tsunami,” they added.

What is an earthquake?

Earthquakes are one of the most disastrous natural phenomena that consist of release of strain energy underneath the ground at a particular location causing tremendous ground-shaking. This happens when stress accumulating at that location over a certain period of time crosses the limit of strength of the material holding it there.

What happens when earthquake strikes?

A tremendous amount of energy gets released in terms of seismic waves and these waves start propagating away from the source. They shake the ground vigorously and cause damage to the human built environment.

Do earthquakes happen often?

Millions of earthquakes occur every year of which many are very small in size and, hence, generally not felt or cause damage. The regions more susceptible to earthquakes are weaker zones of the earth’s crust and are generally located at plate boundaries.