Posted on 03/17/2005 3:59:46 AM PST by TigerLikesRooster
18:00 16 March 2005
NewScientist.com news service
Katharine Davis
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Indonesia and Germany signed an agreement this week to install a tsunami early warning system in the Indian Ocean. Though some of the pieces will be in place by October, it could turn out to be a race against time.
The quake that caused last year's devastating tsunami has increased the stress on other faults nearby, according to a study published this week. This has left the region primed for one or two major earthquakes, and possibly another tsunami.
The earthquake on 26 December, 2004, occurred when the dense India tectonic plate slipped under the Burma plate. This deformed the seabed leading to the tsunami that claimed hundreds of thousands of lives.
When an earthquake occurs in such a subduction zone, where one plate slips under another, it is often followed by another, in addition to the aftershocks. For example, on the Nankai subduction zone to the south-east of Japan, five of the last seven major quakes were followed within five years by major earthquakes along an adjoining segment of the fault, and three of those occurred within a year.
"Big earthquakes make other big earthquakes more likely," says John McCloskey of the University of Ulster, UK, who led a study that measured the changes in stress in the plate boundaries in the Indian Ocean and Sumatra (Nature, vol 434, p 291). This is because a big earthquake often increases stress in other sections of the same fault or those nearby.
McCloskey, working with Suleyman Nalbant and Sandy Steacy, found a dramatic increase in stress in the Sumatra fault, which cuts through the island of Sumatra and runs east of the subduction zone that ruptured last year. The Sumatra fault is a "strike-slip" fault in which two plates slide against each other horizontally.
Before the India-Burma subduction fault gave way, it was pushing on the Sumatra fault, "clamping it shut" says geophysicist Rob McCaffrey of Rensselaer Polytechnic Institute in Troy, New York, US. "When it's clamped it's hard to make it slide. Now there's an increased probability of it slipping."
McCloskey's team found that in places the stress along the Sumatra fault had increased by 9 bars. In 1999, the magnitude 7.4 Izmit earthquake in Turkey increased stress in a nearby plate boundary by just 2 bars, and triggered an earthquake of magnitude 7.1 three months later. McCloskey warns that a magnitude 7.5 earthquake could occur along the Sumatra fault.
While it would not cause a tsunami because the fault line is not beneath the ocean, a magnitude 7.5 earthquake under Sumatra would be devastating. "This one will be closer to buildings, maybe in Medan," says geologist Roger Bilham of the University of Colorado at Boulder, US.
The Sumatra fault is not the only threat. A second quake along the Sunda trench, a continuation of the India-Burma subduction zone, could lead to another tsunami. An earthquake in this area was considered overdue even before the quake farther north on the same fault which caused last year's tsunami.
"This south-east part of the subduction zone has been accumulating stress since 1833 and 1861, and the recent earthquake will have added more," says Phil Cummins of Geoscience Australia.
An earthquake in the Sunda trench could potentially reach magnitude 8.5, McCloskey warns, and could trigger another tsunami. Because it would start further south than the one last year, it would probably not strike Thailand, but Sri Lanka and the west coast of Africa could be hit again, as would Sumatra. Seismologist Seth Stein of Northwestern University at Evanston, Illinois, agrees: "If the next bit south broke it could create a comparable tsunami."
McCloskey's calculations show the stress along the Sunda trench to be about 5 bars. However, there is some uncertainty because of how the Earth's lower crust is reacting to the sudden movement of the upper crust on 26 December. It is therefore possible that that the movement of the lower crust could ease the stress in the Sunda trench, making an earthquake less rather than more likely, McCloskey says.
Peter Malin of Duke University in Durham, North Carolina, US, agrees. "We have huge holes in our data and knowledge of fault zones," he says. And it's equally difficult to say when an earthquake would occur. "We are very bad at predicting the timing of when the pressure will be released," says Bilham. "It could be months, it could be years."
But the threat of another tsunami, however speculative, has prompted McCloskey to call for a tsunami warning system in the Indian Ocean. "It's the closest we've come to a political statement," he says. "We're asking for a political response to a scientific paper." The Indonesian-German venture could be the answer.
Quake Club, Ping!
The good old trick of after hours prophets
I doubt it.
Notice that I didn't imply that there would be no more major quakes there...
I noticed, but my statement stands.
Bad news for Diego Garcia, too?
Here is an earthquake ping.
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