Expert warns of another quake in the Andaman region

Ruins left over from the 2004 temblor that nearly destroyed Banda Aceh.

A fierce earthquake from the Nicobar Islands could strike over Songkran, sending a tsunami crashing into the Andaman Coast, an expert warned yesterday after finding that the 8.6magnitude Sumatran tremor three days ago was exceptionally deep.

"Whenever there is a quake rooted in the [Earth's] mantle, a following quake will be likely in the next few days," said Professor Thanawat Jaruphongsakul, a senior seismologist at Chulalongkorn University.

Fear of another devastating tsunami panicked Thailand and Southeast Asia on Wednesday.

An underwater quake, with its epicentre at the Nicobar Islands, about 150 kilometres north of Aceh on Sumatra, would affect six coastal provinces of Thailand on the Andaman Sea, especially Ranong, which lies closest to a fault line connecting with the Nicobar Islands, he said.

The quakes on Wednesday originated from mantlelevel crust, 20 kilometres below the Earth's surface, which is regarded as a layer that would cause very high magnitude tremblers.

The quake that hit Japan in March came from a shallower layer, so it would take up to 100150 years for the next quake. However Wednesday's quakes, with their epicentre at Aceh, followed just eight years after the massive one that triggered a continentwide tsunami that killed hundreds of thousands of people in many countries, he said.

"Why did Wednesday's quakes emerge just eight years afterwards? This is new to most seismologists and geologists, who are unfamiliar with quakes with depth rooting to the mantle layer," he said.

Seismologists were closely watching and cautiously studying the 9.0 quake that devastated Sendai in Japan on March 11 last year. The first tremor on March 9 was recorded at 7.3 on the Richter scale. That one was understood by seismologists as the main shock, but there were two aftershocks on an even greater scale at 9.0 on March 11 that followed, he said.

The tsunamis created on Wednesday were not powerful or harmfully high because the quake was the horizontal dipslide type. But a mantlebased quake at an island with active underwater volcanoes located north of the Nicobar Islands would probably be a vertical strikeslip type, which would directly impact the six Thai coastal provinces, and possibly deluge them with tsunamis, he added.

Professor Michio Hashzume, a wellknown Japanese seismologist, said Wednesday's quakes were a new type known to have started in the mantle. It was difficult to tell whether a new quake would follow within a few days, like the Sendai quakes, which were similar to Wednesday's quakes. Then there was a 7.3, followed by a 9.0 two days later.

If there are quakes near the Nicobar Islands, they may cause huge collapses in the seabed and outer crust. The seabed may rise and form new islands, he said.

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