Sumatra Poised for Another Tsunami, Study Says

June 8, 2005

The earthquake- and tsunami-battered region of Sumatra, Indonesia, is at risk for more temblors and killer waves, seismologists cautioned today in a new study.

Study co-author John McCloskey, a seismologist at the University of Ulster in Northern Ireland, said the finding adds urgency to the push for greater earthquake and tsunami preparedness in the Indian Ocean region.

"We should assume it will happen in the near future and do as much as quickly as we can," he said. "For governments to take their eye off the ball of preparedness would be irresponsible."

The seismologists calculated the stress changes induced by the March 28 earthquake—the second giant quake within three months along the Sunda trench west of Sumatra. Their findings are reported in tomorrow's issue of the journal Nature.

The calculations suggest the region of the Sunda trench that is beneath the Mentawai islands is now at the greatest risk of rupture. This section is south of the epicenters of the December 26, 2004, and March 28 earthquakes that rattled the region.

The magnitude 9.1 December earthquake triggered the tsunami that killed an estimated 300,000 people in Asia.

According to McCloskey and colleagues, stress changes induced by the December earthquake caused a magnitude 8.7 earthquake in March, killing about 2,000 people on the island of Nias, west of Sumatra.

"The chance of the earthquakes not having been related is vanishingly small. There's no doubt one was caused by the other," McCloskey said.

Greatest Threat

According to the latest calculations by McCloskey and colleagues, the stress change at Nias induced by the December 26 earthquake was tiny: between 0.07 and 0.17 bars. One bar of stress is equivalent to atmospheric pressure at sea level—about 14.7 pounds per square inch (6.7 kilograms per every 6.5 square centimeters).

"There are many examples of a very small stress triggering a large earthquake. This was one of them," McCloskey said.

This concerns the seismologists. Their calculations show that the stress change beneath the Batu and Mentawai islands, caused by the March quake, is similar to the earlier change in Nias that triggered the March event.

Continued on Next Page >>


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