An Earthquake Devastates Sichuan

In the early afternoon of May 12, 2008, a powerful earthquake struck Sichuan province in southwestern China. Centered in Wenchuan County, roughly 80 kilometres west-northwest of the provincial capital of Chengdu, the rupture measured magnitude 8.0 on the surface-wave scale and had a focal depth of 19 kilometres. The main tremor lasted around two minutes as underground faulting tore through the Longmenshan Fault system for more than 240 kilometres. Strong shocks propagated across much of the continent, causing tall office towers to sway as far away as Beijing, Shanghai, and Bangkok.

The United States Geological Survey, which rates the quake at magnitude 7.9, attributes it to shallow faulting on the northwestern edge of the Sichuan Basin, where crust moving east from the Tibetan Plateau pushes against the stronger crust beneath the basin. Its modelling indicates that the slip spread across a fault area of roughly 250 by 30 kilometres, propagating toward the northeast. The region had suffered destructive earthquakes before: a magnitude 7.5 quake on August 25, 1933, killed more than 9,300 people. In 2008 the shaking reached intensity XI in the Wenchuan area, and the USGS lists the quake as felt as far away as Bangladesh, Taiwan, Thailand and Vietnam.