Tsunami threat not over, experts warn
Published: 12/04/2012 at 07:00 PMOnline news: Local News

The government should stay alert for the possibility of another major earthquake and potential tsunami for at least another two days following Wednesday's huge quake and aftershocks off northern Sumatra, experts said on Thursday.

At 3.38pm Bangkok time on Wednesday an 8.6 magnitude earthquake occurred, centred 431 kilometres north of the Indonesian city of Banda Aceh, Sumatra, and was followed by a series of strong aftershocks.

It was centred about 100km from the centre of the 2004 earthquake that generated tsunamis that ravaged Thailand's Andaman Sea coastal provinces and caused a huge loss of life throughout the Indian Ocean region.

Wednesday's earthquake epicentre was located at a depth of 22.9km in the earth's mantle layer.

It was felt in Thailand, India, Malaysia and other countries around the Indian Ocean rim and prompted authorities to issue tsunami warnings and order evacuations.

The tsunami warning sent people fleeing to higher ground in Phuket, Krabi, Phangnga, Ranong, Satun and Trang provinces. It was lifted several hours later without any report of damage or casualties in Thailand. Thursday it was reported that five people were confirmed killed in Sumatra and others injured.

Prof Dr Thanawat Jarupongsakul of the disaster and geographic information study unit at Chulalongkorn University said a close watch is essential over the next few days because experience proved there could be more earthquakes and possible tsunamis in the wake of Wednesday's quake.

He said the quakes' movement was horizontal, rather than vertical, and it was the transform fault or transform boundary which generated the very small tsunami waves.

Following the quake and aftershocks, tsunami waves of about 10 centimetres high were reported at Phangnga.

Because the 8.6 earthquake was shallow, only 22.9km into the mantle layer, and followed by more than 20 strong aftershocks, there was a chance there could be more earthquakes in the area with the potential to generate a tsunami, he said.

"The main surveillance area is the active volcano of Barren Island," he said.

It was part of the Indian subcontinent, located in the east Andaman Sea and part of the Andaman Nicobar chain of islands, about 670km from Thailand.

"If it really triggers other quakes, especially around Barren Island, tsunami waves would reach six provinces in southern Thailand after only half an hour," Prof Thanawat said.

He said his warning was from the lesson learned from the 2011 great earthquake and tsunami in Japan.

On March 9 last year, Japan was struck by a 7.3 magnitude earthquake that triggered a small tsunami.

Two days after that, a second powerful, magnitude 9.0, earthquake hit Japan, leading to a massive tsunami which caused a huge loss of life and immense property damage. It was totally unexpected.

"So, the situation is unpredictable and we should keep a close watch for earthquakes and possible tsunamis for at least two days. I do not want to alarm people, but they should keep abreast of the news.

"And we will lose nothing by being alert. Better to be safe than sorry," he said,

Mr Thanawat said the government needs to communicate better with the people and earthquake and tsunami specialists were needed to study and follow up on natural disasters which affect the country.

He appreciated the fact the government issued a tsunami warning and ordered an evacuation to higher ground, but statistics showed that only three in 10 warnings were right on average.

Prof Dr Michio Hashzume, a Japanese tsunami expert and consultant to the unit, said several huge earthquakes in Japan had been pre-shocks, as other worse quakes occurred afterwards.

He said Japan was regularly struck by earthquakes but skilled scientists in his country still could not correctly predict when they would occur.

"You should keep a close eye on what might happen next. And the Thai government did well to issue an evacuation order, which is the best way to save people, even if it does not happen.

"Do not be discouraged," he said.

BANGKOK POST