Science News

China's big earthquake doubles chances of more

Survivors watch rescuers clear the debris of collapsed buildings in Renhe village in the earthquake-hit area of Shifang, Sichuan province, May 21, 2008. REUTERS/Aly Song

WASHINGTON (Reuters) - China’s giant earthquake in May near Chengdu caused so much geologic stress in the Tibetan Plateau that it doubled the chance of more big quakes along three neighbouring faults, scientists reported.

“The magnitude 7.9 quake on 12 May has brought several nearby faults closer to failure and could trigger another major earthquake in the region,” the American Geophysical Union said in a statement.

This happens because of a domino-like effect where the movement of one piece of Earth’s crust forces another piece to move up, down and away, geophysicists reported.

“One great earthquake seems to make the next one more likely, not less,” said Ross Stein of the U.S. Geological Survey. “We tend to think of earthquakes as relieving stress on a fault. That may be true for the one that ruptured, but not for the adjacent faults.”

The May quake that killed nearly 70,000 people and made 5 million homeless occurred along the Longmen Shan fault. This rupture in the Earth doubled the probability of future earthquakes along the Xianshuihe, Kunlun, and Min Jiang faults, which lie about 90 miles to 280 miles (150 km to 450 km) from the Longmen Shan fault, the scientists said.

Writing in Tuesday’s edition of Geophysical Research Letters, the scientists estimated a 57 percent to 71 percent chance of another earthquake of magnitude 6 or greater in the region in the next decade.

There is an 8 percent to 12 percent chance of a quake of magnitude 7 or higher in the next decade; over the next 30 years, the chance of a magnitude 7 quake in this region rises to 23 percent to 30 percent.

Asia’s Tibetan Plateau in central Asia is one of the most seismically active regions in the world. Large aftershocks in the Sichuan area of China on August 1 and August 5 may fit the geophysicists’ predictions, said the researchers, led by Shinji Toda of the Geological Survey of Japan.

More information and maps of the area showing geological stress on the three nearby faults are available onlinehere.

Reporting by Deborah Zabarenko; Editing by Maggie Fox and Eric Beech