Researchers fear that the magnitude-7.9 earthquake that struck near the major city of Chengdu today will easily be China's biggest killer since 1976's Tangshan quake, conservatively estimated to have taken 250,000 lives. "I would think there's going to be horrific loss of life in this one," says seismologist Lucile Jones of the U.S. Geological Survey (USGS) office in Pasadena, California. The all-too-familiar combination of millions of people living by a major fault rupture in quake-vulnerable structures makes for an inevitably bad outcome, she says.
The Eastern Sichuan quake ruptured about 275 kilometers of a fault running northeastward between the easternmost mountains of the Tibetan Plateau and the densely populated Sichuan Basin. Chengdu, population 11 million, lies about 100 kilometers southeast of the epicenter. Jones studied the fault 25 years ago as a major threat because plate motions are pushing the mountains in the west upward and to the east along the thrust fault and over the basin. "This is the big earthquake for Sichuan," she says. "It's like San Francisco or Los Angeles having its big one."
According to data compiled by USGS in the aftermath of the quake, millions of people suffered strong shaking that would have caused heavy damage. USGS calculates that a total of 6.2 million people would have felt severe to extreme shaking that could cause heavy to very heavy damage to structures vulnerable to seismic shaking. Many structures in China are vulnerable, Jones notes. Another 11.7 million people would have felt very strong shaking capable of moderate to heavy damage to vulnerable structures. The 1976 quake--a magnitude-7.8--struck the city of Tangshan (population 1.5 million), leaving two buildings standing, Jones says. If that's any guide, Sichuan has "got to be really bad," she says.