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Serving Sri Lanka

This web log is a news and views blog. The primary aim is to provide an avenue for the expression and collection of ideas on sustainable, fair, and just, grassroot level development. Some of the topics that the blog will specifically address are: poverty reduction, rural development, educational issues, social empowerment, post-Tsunami relief and reconstruction, livelihood development, environmental conservation and bio-diversity. 

Thursday, June 23, 2005

Faultlines primed for new tsunami

Daily News: 20/06/2005"

THE Boxing Day earthquake has increased the likelihood of more devastation in the region, reports Mark Henderson

The vast earthquake that triggered the Indian Ocean tsunami on Boxing Day last year could yet set off repeats of both events because it has destabilised two neighbouring fault lines.

New research by British scientists has revealed that the magnitude 9.3 quake off the coast of Indonesia has dramatically increased stress on the Sumatra and Sunda Trench faults, both of which are now primed to deliver another major earthquake.

Should a fresh quake take place on either of the faults, the regional consequences would be devastating, though not quite on the scale of the December catastrophe, which has claimed an estimated 300,000 lives.

A rupture of the Sumatra fault, which is considered slightly more likely, would generate an earthquake of magnitude 7 to 7.5 close to Banda Aceh, the city that was virtually wiped out by the December 26 event, but there would be no tsunami, as the fault lies on the mainland.

Should the Sunda Trench tail, however, the consequences would be more severe still. The quake is predicted to reach a magnitude of 8 to 8.5 and its location 135 miles (200km) from the Sumatra coast would generate another tsunami.

Parts of Sumatra that escaped the December tsunami would be inundated with similar walls of water and the earthquake would be too close for a tsunami early warning system to raise the alarm.

Waves would also propagate west across the Indian Ocean, although their destructive impact would be less than those generated by the December catastrophe. The orientation of the Sunda Trench fault means the main westbound tsunami would not crash ashore before reaching South Africa, and the great distances it would have to cross would dissipate much of its energy.

John McCloskey, of the University of Ulster, who led the research team, said that the finding show that the region most severely hit by the Boxing Day tsunami to be at severe risk from related events.

"We can't say at this stage how soon these quakes are likely to happen, but earthquakes tend to cluster in time," he sad, "One of the best indications you're going to have an earthquake is that you've just had an earthquake.

"It underlines the need for a tsunami warning system in the Indian Ocean, and even this wouldn't be much use to the Sumatran coast as the distances are so small,"

In the study, details of which are published today in the journal Nature, Dr. McCloskey's team calculated the extra stress placed on the Sumatra and Sunda Trench faults by the slip on the Sumatra-Andaman fault on December 26.

The Sunda Trench fault is the southern extension of the fault that caused the Boxing Day tsunami, while the Sumatra fault runs parallel. They found an increase of up to nine bars of pressure on the Sumatra faults, and up to five bars on the Sunda Trench. These compare with an increased pressure of four bars before the magnitude 7.4 Izmit earthquake that struck Turkey in 1999.

"You can't draw direct parallels and say therefore the probability is four times more likely than Izmit, but you can get a feel for the increased risk of an earthquake on this fault," Dr. McCloskey said.

He said that the Sunda Trench appeared to pose the more deadly risk. "Earthquakes on this fault triggered lethal tsunamis in 1833 and 1861, and they tend to be big ones," he said.

"Sumatra would be hit hard, but we would expect the propagating wave to do less damage elsewhere than in December. The energy moves mainly laterally, so it would head towards South Africa and the Southern Ocean.

Distance lessens impact considerably: only about 200 people were killed in East Africa in December, compared to more than 100,000 in Indonesia." It is impossible to say how soon another earthquake will occur, but team pointed out that coupled earthquakes in Japan have happened within a year of one another in the past.

Dr. Richard Teeuw, of the University of Portsmouth, said: "If another Indian Ocean tsunami were generated in the near future, there would still be great loss of life close to the earthquake epicentre. However, in regions where the tsunami will take hours rather than minutes to arrive, this time round there would probably be fewer fatalities."

Courtesy: The London Times


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