PADANG, INDONESIA — Expect a far more powerful earthquake than last week's magnitude 7.6 temblor to hit Indonesia's devastated Padang area in the next few decades.
That's the word from a team of leading seismologists, who said the worst is yet to come, although they cautioned that predicting the timing of earthquakes is an inexact science at best.
After a three-day review of seismic evidence using global-positioning equipment, scientists with the Earth Observatory of Singapore, or EOS, found that the earthquake that hit the Indonesian city of Padang did little to relieve the stored tension at the juncture of two tectonic plates.
The EOS team believes that the eventual energy release could result in an earthquake close to the scale of the magnitude 9 monster that triggered the 2004 Indian Ocean tsunami, killing more than 200,000 in a dozen countries.
"We don't think this was the big one," said Paramesh Banerjee, technical director of EOS, a $700-million government-funded institute for the study of tsunamis, volcanoes, earthquakes and climate. "It can happen any time -- now, in 20 years or more."
On Monday, rescue workers ended their search for life beneath the rubble, shifting their focus instead to helping survivors in the area around Padang, a port city of 900,000 on Sumatra island. But their efforts were hampered by torrential rain.
The government's official death toll stood at 603, although the United Nations said 1,100 people died and other disaster specialists said the number will probably climb to several thousand after more corpses are unearthed.
Gagah Prakoso, a spokesman for the Indonesian Search and Rescue Agency, told reporters that chances of anyone surviving this long without food and water were slim, prompting the decision to concentrate on finding bodies and cleaning up the rubble.
Indonesia faces a huge rebuilding task. More than 88,000 houses and 285 schools were destroyed in 10 districts, according to the U.N. and Indonesia's Disaster Management Agency, with an additional 100,000 public buildings and 20 miles of road damaged.
Seismologists said the earthquake occurred in the collision zone where the Indo-Australian Plate dives beneath the Sunda Plate, which is below Padang and the Indonesian province of Aceh, which was battered by the 2004 earthquake and tsunami.
"When one plate goes beneath another it's called 'subduction,' " Banerjee said. "But it doesn't go smoothly. It gets stuck and then it slips. This slip is an earthquake."
According to Richard Briggs of the U.S. Geological Survey, these plates converge, colliding at a few inches a year, with the stress stored for decades or centuries before being released suddenly as large, damaging earthquakes. The magnitude of the earthquake depends on the size of the fault and how much the fault slips during a sudden rupture.
In the case of the Sunda megathrust fault, which parallels the west coast of Sumatra, the 850-mile northern portion slipped as much as 100 feet in 2004, triggering the tsunami. In 2005, a 210-mile portion directly to the south slipped more than 40 feet during the magnitude 8.7 earthquake that devastated the Nias, Banyak and Simeulue islands.
The portion of the fault next in line, offshore Padang, has yet to slip despite the most recent quake, according to the EOS.
The idea that a mammoth earthquake is coming to Padang is nothing new to paleoseismologist and EOS director Kerry Sieh, who has been studying the regions' tectonics for the last 18 years. Sieh's team has identified the sequence of Padang-area earthquakes using GPS data, historical records and the growth patterns of coral based on its uranium content.
Since the December 2004 tsunami, the scientists have produced papers and statements and spoken to local officials about the risk. With partial financing from the California Institute of Technology, where he had been a professor, Sieh printed posters in English and Indonesian and took them to outlying islands to discuss with village elders and fishermen what he believed was an inevitable earthquake and subsequent tsunami. "They were interested, but we weren't taken seriously," he said.
The city of Padang has tried to foster earthquake and tsunami preparedness by providing public service announcements, seminars and evacuation routes. Still, Wednesday's quake brought a high toll in lives and buildings -- a fact exacerbated by the area's relative poverty and questionable construction standards.
Vice Gov. H. Marlis Rahman acknowledged that the area needs to prepare for the next earthquake. But experts warn that apathy and human nature often take their course.
"The problem is we're too busy with laundry, taking kids to school, catching fish to feed your family to worry about low-probability, low-risk hazards," Sieh said. But, he added, the risk of not preparing for the inevitable is great.
"The people in charge of Padang have had lots of things going on," he said, "but they've got a lot more now."
McDermid is a special correspondent.