Quake speeds repeat of 2004 tsunami

Seismologists have warned last week’s powerful earthquake off western Indonesia has increased pressure on the source of the devastating 2004 tsunami – a fault that could unleash another monster wave.

“The spring was pushed a little bit tighter,” said Kerry Sieh, director of the Earth Observatory of Singapore. The timing of another “megathrust” tremor “could have been advanced by a few years,” he said.

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The two last giant quakes occurred around 1393 and 1450, and Mr Sieh said the 2004 quake may be just the first part of a similar couplet.

Stresses loading up on the fault for centuries were relieved only partly eight years ago, he said. And last week’s tremor effectively squeezed the overlapping tectonic plates that form the fault.

He said: “The next megathrust rupture could be in 50 years or in five. It’s impossible to know.”

A separate section of the fault, hundreds of miles to the south, could snap within the next 30 years, sending a tsunami crashing into Padang, a low-lying Sumatran city of one million.

Last week’s quake was a “strike slip”, which means it thrust from side to side, not vertically, and so did not generate a large tsunami.

Danny Hilman Natawidjaja, a geologist with Indonesia’s Institute of Science, agreed this had piled stress on the megathrust, and that “both Aceh and Padang need to be prepared”.

The 8.6-magnitude quake also showed tsunami-ravaged Aceh province, close to the epicentre, remains unprepared for the next Big One. Though the quake damaged little, Indonesia’s disaster-management chief said evacuation efforts were “a big mess.”

Indonesia, located on the “Ring of Fire,” an arc of volcanos and fault lines encircling the Pacific Basin, has unleashed some of the deadliest seismic events of the past century. But the 9.15-magnitude quake that struck in 2004, triggering a 100ft-high tsunami and killing 230,000 people, caught scientists off guard because its fault, west of Sumatra, had long been quiet. Since then scientists have conducted a flurry of research, looking at tsunami sand deposits, coral and GPS data.

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Countries along the Indian Ocean have spent millions of pounds installing buoys capable of detecting waves generated by seismic activity, and building up a vast communications network, from alarms on beaches to systems that deliver warnings by TV, radio, internet and mobile phone text message.

But last week’s quake shows that Aceh has a long way to go, even though the only deaths were from heart attacks.

Had it been the next Big One, sending waves crashing to shore within 30 minutes, tens of thousands could have died in Aceh, where about three-quarters of the 2004 deaths occurred.

Traffic came to a standstill as the provincial capital, Banda Aceh, emptied, people piling into cars and motorbikes to try for high ground. Many said that after two hours they had only moved six miles. Some left their vehicles and started walking.

“It was a big mess,” said Syamsul Maarif, head of the national disaster management agency.

“What we found out last week was that evacuations were nothing like the simulations.”

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