Indonesia Aceh quake triggers Indian Ocean tsunami alert

BBC News 11 Apr 12;

An earthquake with an magnitude of 8.7 has struck under the sea off Indonesia's northern Aceh province.

The quake triggered a tsunami watch alert across the Indian Ocean region.

The Pacific Tsunami Warning Center (PTWC) said it was not yet known whether a tsunami had been generated, but advised authorities to "take appropriate action".

The region is regularly hit by earthquakes. The Indian Ocean tsunami of 2004 killed 170,000 people in Aceh.

The US Geological Survey (USGS), which documents quakes worldwide, said the Aceh quake was centred 33km (20 miles) under the sea about 495km from Banda Aceh, the provincial capital.

It was initially reported as 8.9 magnitude but was later revised down to 8.7 by the USGS. Strong aftershocks were also reported.

The PTWC alert said quakes of such a magnitude "have the potential to generate a widespread destructive tsunami that can affect coastlines across the entire Indian Ocean basin".

But Bruce Presgrave of the USGS later told the BBC that the nature of this quake made it less likely a tsunami would be generated, as the earth had moved horizontally, rather than vertically, therefore had not displaced large volumes of water.

"We can't rule out the possibility, but horizontal motion is less likely to produce a destructive tsunami," he said.

Sutopo, a spokesman for Indonesia's disaster mitigation agency, said the quake had been felt "very strongly".

"Electricity is down, there's traffic jams to access higher ground. Sirens and Koran recitals from mosques are everywhere," he told Reuters.
'Minute of chaos'

The earthquake monitoring agency in Indonesia said the tsunami warning would remain in place for another few hours, but that there had been no reports so far of a low tide, which would indicate the water was receding before building into a tsunami.

The tremor was felt as far away as Singapore, Thailand, Sri Lanka and India.

"There was a tremor felt by all of us working in the building," a man called Vincent in Calcutta, India, told the BBC.

"All just ran out of the building and people were asked not to use the elevator. There was a minute of chaos where all started ringing up to their family and asking about their well-being."

The Thai office of disaster management said people along the coasts of Phuket, Phang Na and Andaman province should heed warnings and evacuate.

Tsunami warning sirens, set up in many vulnerable areas after the 2004 disaster, were heard in Phuket, where correspondents said people were calmly following evacuation routes to safe zones.

Indonesia straddles the Pacific Ring of Fire, a zone of major seismic activity.

The BBC's Karishma Vaswani in the Indonesian capital, Jakarta, says there were reports of the ground shaking for up to five minutes. Contact with people in the immediate area around the quake has not been possible so far, says our correspondent.

Huge quake strikes off Indonesia, tsunami warning issued
Reza Munawir Reuters Yahoo News 11 Apr 12;

BANDA ACEH, Indonesia (Reuters) - An 8.7 magnitude earthquake struck off Indonesia on Wednesday, sending residents around the region scurrying from buildings and raising fears of a huge tsunami as in 2004, but authorities said there were no reports suggesting a major threat.

Indonesian President Susilo Bambang Yudhoyono said there were no immediate reports of casualties or damage in Aceh, the Indonesian province closest to the earthquake.

The quake struck at 0838 GMT and the Pacific Tsunami Warning Center said soon afterwards a tsunami watch was in effect for the entire Indian Ocean. It later said the threat of a big tsunami had receded, although the warning remained in place.

"It doesn't look like a major tsunami. But we are still monitoring as tsunamis come in waves," Victor Sardina, a geophysicist on duty at the Hawaii-based institute, told Reuters.

Individual countries, including Thailand, Indonesia, Sri Lanka and India, issued their own warnings.

People near the coast in six Thai provinces were ordered to move to higher ground and authorities shut down the international airport in the beach resort town of Phuket.

The quake struck 308 miles (500 km) southwest of the city of Banda Aceh, on the northern tip of Indonesia's Sumatra island, at a depth of 20.5 miles (33 km), the U.S. Geological survey said.

Indonesia's disaster management agency said power was down in Aceh province and people were gathering on high ground as sirens warned of the danger.

"The electricity is down, there are traffic jams to access higher ground. Sirens and Koran recitals from mosques are everywhere," said Sutopo, spokesman for the agency.

But Yudhoyono said there were no signs of a disaster.

"There is no tsunami threat although we are on alert," said he said at a joint news conference in Jakarta with visiting British Prime Minister David Cameron, who said Britain was standing ready to help if needed.

"The situation in Aceh is under control, there's a little bit of panic but people can go to higher ground," Yudhoyono said.

He said he had ordered a disaster relief team to fly to Aceh, which was devastated by the 9.1 magnitude 2004 quake, which sent huge tsunami waves crashing into Sumatra, where 170,000 people were killed, and across the Indian Ocean.

In all, the 2004 tsunami killed about 230,000 people in 13 Indian Ocean countries, including Thailand, Sri Lanka and India.

"HORIZONTAL SHIFT"

Wednesday's quake was felt as far away as the Thai capital, Bangkok, and in southern India, residents said.

Hundreds of office workers in the Indian city of Bangalore left their buildings while the Indian port of Chennai closed down because of the danger of a tsunami, the port said.

The quake was in roughly in the same area as the 2004 quake which was at a depth of 18 miles (30 km) along a fault line running under the Indian Ocean, off western Indonesia and up into the Bay of Bengal.

One expert told the BBC the Wednesday quake was a "strike-slip" fault, meaning a more horizontal shift of the ground under the sea as opposed to a sudden vertical shift, and less risk of a large displacement of water triggering a tsunami.

The quake was also felt in Sri Lanka, where office workers in the capital, Colombo, fled their offices, and in Phuket, both of which were hit hard by the 2004 tsunami.

Mahinda Amaraweera, Sri Lanka's minister for disaster management, called for calm while advising people near the coast to seek safety.

"I urge the people not to panic. We have time if there is a tsunami going to come. So please evacuate if you are in the coastal area and move to safer places," Amaraweera told a private television channel.

In Bangladesh, where two tremors were felt, authorities said there appeared to be no threat of a tsunami. Australia also said there was no threat of a tsunami there.

(Reporting by Jakarta, Bangalore and Bangkok bureaus; Writing by Robert Birsel; Editing by Raju Gopalakrishnan)