The Disastrous M 7.9 Sichuan Earthquake of 12 May 2008

Abstract

On 12 May 2008 an earthquake of magnitude 7.9 devastated the Northwestern Sichuan province of China. This earthquake occurred along the northeast trending Longmenshan fault bordering the Tibetan plateau on the west and the Sichuan Basin on the east. The focal mechanism depicts a thrust fault mechanism with the Northwest dipping fault plane correlating well with the tectonic fault. This plane also hosts a component of right-lateral strike slip consistent with the local tectonics and orients well along the trend of aftershock distribution. Broadly, the Sichuan earthquake is a consequence of the northward convergence of the Indian plate against the Eurasian plate resulting in eastward crustal extrusion of Tibetan plateau accompanied by clockwise rotation of several tectonic blocks of the Eurasian landmass. More specifically, it occurred along the Northeast trending Longmenshan fault, due to over-thrusting of a weak Tibetan crustal block over a mechanically stronger Sichuan Basin. Estimation of p value using about 164 aftershock data provides a value of 0.87, comparable to a value of 1.0 obtained for the Muzaffarabad earthquake in western Himalaya, indicating a normal rate of decay of the aftershocks in the months ahead. We infer that aftershocks of magnitude exceeding 5 may occur for a duration of about 7 months.