Next Big One will strike Sumatra within decades

Kerry Sieh predicts an 8.8 quake that could affect a million people; he hopes govts will heed the work of geologists
Chang Ai-Lien, Straits Times 14 Oct 09;

AS PROPHETS of doom go, geologist Kerry Sieh is a fairly mild mannered version but he more than compensates by having a pretty terrifying tale to tell.

It centres on Padang and the tectonic time bomb it is sitting on.

The five major quakes that have struck the Sumatran city this decade are forming a kind of seismic countdown to the king hit Professor Sieh fears is approaching.

'There are many, many dangerous tectonic animals across the globe, and who knows which is going to strike next. But there's a tiger in Padang and it's going to bite in the next few decades,' he warns.

The 7.6-magnitude quake that hit two weeks ago left parts of the city flattened and thousands dead and injured but that was just a prelude to the main event, he says.

'There's no place on earth that has released so much seismic activity in the past decade as western Sumatra,' adds Prof Sieh, director of the Earth Observatory of Singapore at Nanyang Technological University (NTU). 'The failure sequence started in 2000.'

Sliding left hand over right, Prof Sieh, 59, illustrates how some of these were caused by the relentless grinding of massive chunks of the earth's crust along the Sunda megathrust, a 2,000km fault line running parallel to Sumatra.

He and his Indonesian colleagues are now eyeing a 400km section beneath the Mentawai Islands west of Sumatra. Although it has remained intact for hundreds of years, it is under tremendous and increasing stress.

When - not if - it reaches its breaking point, it will trigger an earthquake similar to the one that caused the 2004 Boxing Day tsunami.

The prediction: an 8.8-magnitude quake within a few decades.

Seismic data shows that last month's quake was not caused by a rupture of the Sunda megathrust, but about 20km beneath it.

Prof Sieh is as certain of this prediction as scientists get.

He has narrowed the timeframe to mere decades - a small window in a field where scientists more commonly study patterns in land and rock formations spanning hundreds or thousands of years.

The evidence comes from measurements made with the global positioning system (GPS) which tracks horizontal and vertical land movement, and recovering prehistoric data from coral, which record sea-level changes in their growth patterns over the centuries.

His team found that Sumatra has been hit by a sequence of large earthquakes caused by ruptures along the Sunda megathrust about every 200 years: in the 1300s, 1600s and 1800s.

So the next one is coming, he says, and Sumatra's central western coast will be ground zero.

Picking up an age-worn globe, he points to the exact spot where the quake will hit and its likely trail of destruction.

Because it will be further south than the 2004 quake, any tsunami would be most serious along the central western coast of Sumatra, and in the opposite direction, south-west heading to Mauritius and South Africa, where the waves would arrive many hours later and have time to dissipate.

But the giant waves could affect more than a million people along the Sumatra coastline, particularly in the densely populated city of Padang.

It is a terrifying force of nature that cannot be stopped of course, but Prof Sieh hopes his early warnings will give residents and policymakers time to act.

'We cannot solve their problems,' says the Iowa-born academic, who came from the California Institute of Technology to head the Earth Observatory last year.

'Our role is to provide the science that helps people make the right decisions, whether it's the parent sending his kid to school or the President of Indonesia distributing relief funds.'

The facility on the NTU campus, which is funded to the tune of $287 million over 10 years, has an international team of 40 scientists and staff studying nature's triple threat of earthquakes, volcanoes and climate change.

Singapore is the perfect, stable spot from which to study volatile earthquake activity nearby.

It is at least 400km from the nearest fault in Sumatra and while tremors are felt here, widespread damage is unlikely.

Researchers are working on using technology to get information quickly from over 30 GPS stations around Sumatra.

'Right now, we have to download the information from most of the stations by hand but we are testing the technologies that will allow us to do so remotely,' says Prof Sieh.

'What I hope to do eventually is to walk into my office in Singapore and be able to look at GPS vectors of earth movements from the previous week on the plasma screens, which will automatically signal anything unusual.'

That is the science, but there is plenty of emotion as well for Prof Sieh, who has been chasing quakes for the last 30 years.

On Sept 30, he had just landed in Singapore from a holiday in Thailand and was in a taxi on the way home when the quake hit Padang.

Two days later, he and his colleagues were taking the latest GPS measurements in western Sumatra.

At one point, he found himself standing in a crowd beside a collapsed school building, watching an excavator attempting to uncover the bodies of children who had not been able to escape.

While some progress has been made by the Indonesian authorities and other groups since 2004 to improve infrastructure, more could be done to make buildings stronger, he said.

'Fewer than 5 per cent of buildings collapsed.

'But that is small consolation to the 70 kids who died in the school, or their friends and families.'

His prediction of the next big quake, however, could make a very big difference by spurring politicians and others into action. Charitable groups and non-governmental organisations (NGOs) have already started.

Some are working in Indonesia to make buildings quake-proof, while others are helping to educate locals. For instance, posters and brochures are being put up in Padang to explain the basics of earthquakes and where to go for help and information.

Residents are taught that if they feel the earth shake for at least 45 seconds, they should flee from the beach in case of a tsunami. They are also told of evacuation routes and not to use cars because of the risk of traffic jams.

And a project undertaken by NTU's Lien Institute For the Environment (Life) is using new, inexpensive ways to retrofit homes in western Sumatra.

Prof Sieh and his team are also producing a document that they hope to give to policymakers and interested parties, so they are clear about the science behind the forecast.

'I don't want it to be a surprise when the next tsunami comes,' he says.

'We are doing all we can to get the word out so that more can be done to save lives.

'When the earthquake happens, although we will have made a contribution to saving lives, there still will be victims. I imagine the moment will be bittersweet.'

He looks into the past to tell future
Straits Times 14 Oct 09;

HE PEERS thousands of years into the past, studying faults and landforms to predict future quakes.

Professor Kerry Sieh was born in Iowa in 1950 to a draftsman father and homemaker mother.

Even as a child, he enjoyed exploring nature and spending time on his grandparents' farm during the summer. He majored in geology at the University of California, Riverside, and later obtained a PhD in geology from Stanford University.

Prof Sieh initiated the field of paleoseismology 30 years ago with his discovery of how often California's San Andreas fault has generated great earthquakes.

The field involves using geological layers and landforms to understand the geometries of active faults, the earthquakes they generate and the crustal structure their movements produce.

Before becoming director of the Earth Observatory of Singapore last year, Prof Sieh was a chaired professor in Caltech's Tectonics Observatory, a US$30 million (S$42 million) privately funded scientific effort, which he and others at Caltech created.

In Asia, his work along the great undersea fault line, the Sunda megathrust, has revealed patterns of ancient rupture and current straining that led to forecasts of recent and impending large Sumatran earthquakes and tsunamis.

He has spent the past six years studying Indonesian earthquakes, and successfully predicted Sumatra's 2005 8.7-magnitude earthquake off Nias. This was likely an aftershock of the Boxing Day earthquake three months earlier.

Based on GPS data and research on coral growth patterns, Prof Sieh believes that a magnitude 8.8 quake will hit Sumatra within 30 years.

He and his students recently completed a six-year study of the active faults of Taiwan, and have begun a comprehensive study of earthquake geology in Myanmar.

Colossal quake may hit Sumatra within 30 years: geologist
Yahoo News 15 Oct 09;

SINGAPORE (AFP) – A colossal earthquake may hit Indonesia's Sumatra island within 30 years, triggering a tsunami and making last month's deadly temblor look tiny by comparison, a geologist has warned.

Kerry Sieh, director of the Earth Observatory of Singapore, said the next big quake would last more than six times as long as the 7.6 magnitude quake which struck western Sumatra on September 30, leveling the city of Padang. "We expect it will be about a magnitude 8.8, plus or minus say 0.1," Sieh, an American professor, said at a presentation late Wednesday at the Nanyang Technological University, where the observatory is located.

He said last month's Sumatra quake lasted about 45 seconds.

"This one'll last about five minutes," Sieh said."This 7.6 is very, very small, minuscule compared to the great earthquakes."

The official death toll reached 1,115 on Wednesday but many more are feared dead after villages were turned into mass graves. Around 100,000 houses are estimated to have been destroyed, leaving about half a million people homeless.

Based on historical earthquake trends from geological analysis of coral specimens from the region, last month's quake was just a precursor, Sieh said.

Likening the pressures under the affected fault to a coiled spring, Sieh said the recent quake "had really very little effect in terms of relieving the spring" which will unleash pent-up energy possibly within the next 30 years.

"If you're a parent who has a child, you have to expect that child's going to experience that earthquake and the tsunami," he added.

A massive tsunami hit Indonesia and other countries in the Indian Ocean rim in 2004, killing about 220,000 people, most of them in Aceh province in northern Sumatra.