Strong aftershock rocks Indonesian seas

An 8.2-magnitude aftershock struck off the coast of Indonesia’s Sumatra island today, following a stronger quake that triggered an Indian Ocean-wide tsunami alert, that was later withdrawn.

The US Geological Survey said the aftershock struck at 1513 IST, 615 km from Banda Aceh.

The strong aftershock followed closely the United States Geological Survey (USGS) discounting the possibility of a devastating tsunami wave being triggered by the original quake event.

This was based on the assumption that the original event might have been 'strike-slip' (horizontal movment of the tectonic plates) as against a mega thrust (involving uplift of the seabed from a vertical plate movement).

The Indian National Centre for Ocean Information Services (Incois) at Hyderabad assessed that earthquakes of this size are capable of generating ocean-wide tsunamis, which can effect the areas in entire Indian Ocean. Authorities should be aware of this possibility.

However, there is no confirmation about the tremors triggering tsunamis so far, the Incois bulletin said. An investigation is underway to determine if a tsunami had been triggered by the earthquake, it added.

There has not been any news of significant wave movement coming in from the Andaman and Nicobar Islands, the first outpost for a tsunami wave travelling from the epicentre of the earlier quake.

Many parts of south Andamans have been put on red alert from a tsunami watch. The wave would not have taken more than a hour's time to travel the distance from the time of the event.

An Indian Ocean-wide tsunami alert was declared after the first quake struck off southwest Indonesia earlier this afternoon.

The intensity almost matched the temblor of 2004 that sent out a killer Sumatran tsunami wave killing more than two lakh people.

The Hyderabad-based Incois earlier issued a 'red alert' watch for a possible tsunami for three points in the Andaman and Nicobar Islands.

These are Indira Point Great and Little Nicobar Island, Komatra and Katchal Island, and Nicobar. Almost the entire peninsular coast in India, both the west and the east, have been put on a 'watch list.' This includes Kudankulam, the site of the about-to-be-commissioned nuclear power plant.

Mr Mahendrato Saraogi, a Kolkata-based businessman told Business Line that no significant wave activity was visible around Port Blair in Andaman and Nicobar. Mr Saraogi has relatives based in the region.

According to Mr Sampurnananda Mahapatra, a senior tsunami and earthquake specialist at the National Disaster Management Authority, the fact that the massive M8.7 quake originated in the sea throws up the possibility of a tsunami 'in real terms.'

He told Business Line not all quakes of this size generate a tsunami unless it involves a 'mega thrust' in which adjoining tectonic plates move up or down. But the location of the quake and the known vulnerablity of the region suggests the possibility of a tsunami wave being triggered.

He was of the view that the wave may have already hit the southern-most point of the Andaman and Nicobar Islands (half-an-hour to one hour subsequent to the event.).

The 'directivity map' of the tsunami wave as depicted by the Hyderabad-based Incois suggests a two-hour wave travel to the Tamil Nadu coast and ahead of it by 30 minutes to Sri Lanka.

It also suggests that the core of the wave might be making its way towards the Maldives.

Meanwhile, sources speaking to Business Line from New Delhi said that the National Disaster Management Agency in New Delhi have not been able to establish contact with the Nicobar Island administration that sits closest to the epicentre to the west-northwest.

Mild tremors were felt in Bangalore. IT offices across the city advised their employees to vacate office buildings.

Different parts of Kolkata also experienced mild tremors around 2.15 pm. Along with the city proper, different parts the adjoining districts also experienced mild tremors.

In Chennai, tremors were felt around 2.30 p.m. The city's arterial Anna Salai and its by-lanes were crowded as people in most commercial complexes rushed out of their buildings.

Traffic jams were reported on Santhome High Road (near Marina beach) and jeep loads of the Rapid Action Force were spotted involved in an evacuation drill.

At a BPO in east Anna Nagar, employees rushed out on to the street from their multi-storeyed building.

“Actually, we did not realise it until I got a call from a colleague who stepped out for tea. In a few seconds, the entire office complex was emptied," said Mr R. Srinivasan, an employee of a power electronics company in T. Nagar.

In many of the software complexes such as the Olympia Tech Park, employees were evacuated from the building.

In homes, people settling down for an afternoon siesta were rudely awakened with cots shaking. In suburban Anna Nagar, people rushed out of their flats. In many apartment complexes, residents stayed outdoors for a while.

Priya Ragavan, a XII standard student of Kendriya Vidyalaya in Anna Nagar, said all the students were evacuated from the school building and sent home. "We were not even given time to collect our bags from the class room," she said.

(With inputs from Our Bureaus in Bangalore, Kolkata and Chennai.)

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