Saturday, May 21, 2011

Predicting the next big quake

By Augustine Anthuvan | Posted: 21 May 2011 1033 hrs

SUMATRA: A Banyan tree - well over a hundred years old - located on Simeulue island, has survived two tsunamis - a big one in 1907 and the recent one caused by the 2004 earthquake.

And those who survived continue to tell the story of the 1907 "Semong", the local word for tsunami.

Kerry Sieh, Director of the Earth Observatory of Singapore, said: "The reason that villagers here were able to escape is because their grandparents, their great grandparents passed down to them the story of what happened in 1907.

"When the tsunami hit in 2004, the water tore all these buildings off their foundations, all you see are the slab foundations, so you can see it was pretty strong. It ripped them off their foundations leaving that little building, leaving the mosque...the wave was about four metres high.

"In 1907, the villagers said that (according to the story), the wave was about 10 metres or they learnt from that event in 1907. That when you feel a big earthquake, you run to the hills as fast as you can. They did that and no one in this village died."

However, Mr Sieh said survival in earthquake prone areas would require looking beyond oral traditions.

"If you pass things down from generation to generation, say like the Pacific North West Indians in the United States did about the big eruption of Mount Mazama in Oregon, 6,000 years of oral tradition, that's wonderful but it's rare and in big cities people don't tend to have these oral traditions.

"What I'm submitting to you is...geology can tell you a lot if you're willing to pay attention to it. Now the Japanese were caught short in that regard recently, even though they were the most prepared people in the world for tsunamis and earthquakes. They didn't pay enough attention to the geological evidence."

Geological evidence of the 1907 earthquake at Simeulue Island is in the form of a coral head, that popped up 1.3 metres out of the water.

"In a sense that's a seismogram, it's a record of an old earthquake," said Mr Sieh.

An island off the west coast of Nias became 10 times its original size after the 2005 earthquake.

Data from coral reef upliftments on this "new" island are helping scientists to understand the patterns of great earthquakes on the Sunda megathrust.

Mr Sieh said: "The corals show and the Dutch records show there was a big earthquake in 1861. After 1861, the island rose but then it slowly subsided, as the megathrust carried the subducting slab down, so it went down...if it kept going down for a couple of decades, this whole island would have disappeared beneath the water.

"But just in time, the next one happened and the island grew again so now its subsiding again. It will subside a centimetre per year over the next century or so and then (it will) pop up come again."

Scientists are now able to forecast the location of where an impending large Sumatran earthquake might hit. But challenges remain. For one, authorities will have to translate that knowledge into planning and changing land use and finding meaningful ways to protect the majority of the people that are likely to be affected.


No comments:

Post a Comment