Oct. 1 (Bloomberg) -- The earthquake that struck the Indonesian island of Sumatra yesterday is likely a harbinger of a bigger tsunami-triggering temblor in the same area, according to a researcher who studies seismic activity in Asia.

The 7.6-magnitude temblor in the city of Padang is part of a cycle of earthquakes that started in 2007 in a 700-kilometer (435 miles) fault line off Sumatra called the Mentawai patch, said Kerry Sieh, a Singapore-based professor of geology from the California Institute of Technology. The cycle may include a quake with a magnitude of as much as 8.8, Sieh said.

“The earthquake yesterday occurred right on the edge of this big patch that we identified over the past few years as being about to fail,” Sieh said in a telephone interview today. “That failure sequence could last anywhere from another 30 seconds to another 30 years. Nobody can say.”

Indonesia forms part of the “Ring of Fire,” an arc of volcanoes and geologic fault lines surrounding the Pacific Basin. The archipelago lies in a zone where four tectonic plates meet and constantly shift, sometimes causing earthquakes that can produce tsunamis.

The 2004 tsunami that swept across the Indian Ocean, devastating coastal communities in countries including Indonesia, Sri Lanka, India and Thailand, was caused by a 9.1-magnitude temblor in the Sunda megathrust. There have been hundreds of quakes in Indonesia since then, according to Sieh.

Earthquakes push up the sea floor, lowering the water level. Changes in water levels are marked by coral growth rings, which Sieh and colleagues studied in the Mentawai patch, a part of the Sunda megathrust that’s shaken by a quake about every 200 years to relieve built-up tension in the plates.

Tsunami Trigger

An 8.8-magnitude quake in the area would set off a tsunami that may be as high as 5 meters (16 feet) at Padang, Sieh and colleagues said in the study last year. An 8.4-magnitude quake that struck in September 2007 was probably the first of a new cycle that includes yesterday’s temblor, he said.

“There’s no city on earth that’s had more wake-up calls than Padang,” Sieh said today. “They’ve had five or six major earthquakes in the last 10 years, and a bigger one to come.”

Yesterday’s earthquake in Padang killed more than 200 people, according to the National Disaster Management Agency. A 6.8-magnitude temblor struck 225 kilometers southeast of Padang in Jambi province at 8:52 a.m. local time today, the U.S. Geological Survey said on its Web site.

To contact the reporter on this story: Simeon Bennett in Singapore at sbennett9@bloomberg.net

Last Updated: October 1, 2009 02:25 EDT