Fault Shift Leaves China Vulnerable to More Quakes

Sept. 12, 2008 -- After a magnitude 7.9 earthquake struck central China last May, killing 69,000 people, injuring hundreds of thousands and leaving millions homeless, geologists believe there may be more devastation to come.

Stress on the nearby Kunlun, Xianshuihe and Min Jiang faults has increased, they say, doubling the risk that one of them will unleash a magnitude 6.0 or 7.0 tremor in the next decade.

Led by Shinji Toda of the Geological Survey of Japan, a team of researchers used data from the massive quake to calculate how tectonic stresses in Earth's crust were redistributed. They found that the Longmen Shan fault, which slipped between 6 and 9 meters (19.7 to 29.5 feet) during the powerful quake was relieved of stress. But faults to the northwest and southwest loaded up on tension, making them more prone to rupture.

Over the next decade, the team estimates there's a 50-50 chance of a magnitude 6.0 quake or greater and a 10 percent chance of a quake of 7.0 or higher on one of the three faults.

"You tend to think a big earthquake relieves stress in the crust, but there are areas that were pushed closer to failure," team member Ross Stein of the United States Geological Survey said.

The idea that a powerful earthquake could lead to chain reactions first took hold in early 2005. The Indian Ocean coastline from Indonesia to Somalia was recovering from the horrifying December 2004 tsunami, which had been sparked by a magnitude 9.2 quake off the coast of Sumatra.