Ancient corals warn of mega quake in Sumatra

December 12th, 2008 - 1:57 pm ICT by ANI  

London, Dec 12 (ANI): The study of ancient corals has led a team of geologists to determine that another huge earthquake may hit the Sumatra region within the next few decades.

According to a report in Nature News, an analysis of fossilized coral beds in the region has revealed that the magnitude 8.4 and 7.9 quakes that hit the island in September 2007 could be harbingers of further, and potentially more destructive, ruptures.

Kerry Sieh, an earthquake geologist at the California Institute of Technology in Pasadena, and his colleagues found evidence for recurring changes in the local sea level, which they attribute to tectonic plates shifting upwards and subsidence of the sea floor sure signs of a quake.

The scientists found evidence in the coral record for three past ruptures of the Mentawai section a 700-kilometre stretch of a 6,000-kilometre-long fault known as the Sunda megathrust.

One of these ruptures occurred around 1350, one around 1600, and the other from 1797 to 1833 each causing two or more earthquakes.

The 2007 quakes, they suggest, may mark the beginning of a new earthquake supercycle in the region, which, if the previous cycles are indicative, might last for a few decades to a century.

The next big earthquake, possibly strong enough to spawn a deadly tsunami that could reach Sumatras coasts within minutes, will probably occur in the lifetime of the islands children and young adults.

Worryingly, Sieh and his team also found that the tremors that initiate a cycle are often soon followed by much stronger quakes.

Given the amount of unreleased pressure that has accumulated since 1833 in the plates off Sumatra, the new cycle could culminate in a magnitude 8.8 quake, they believe.

For Sumatra, the worst is still to come, said Costas Synolakis, an environmental engineer and director of the Tsunami Research Center at the University of Southern California in Los Angeles.

Geologists including Sieh had reported earlier in December that the 2007 Sumatra quakes had ruptured only a fraction of the area that had been ruptured in 18332.

Sieh fears the patch will re-rupture in just a few years or decades, when the stress and strain that has accumulated in stronger parts of the Mentawai section is released.

According to Synolakis, the repetitiveness of the cycles provides the most compelling evidence to date for elastic rebound of previously stored energy, which may result in a tsunami generated by a quake. (ANI)

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