Tectonic Mechanism of the Suining (Ms5.0) Earthquake, Center of Sichuan Basin, China

On Jan. 31 of 2010, the Suining earthquake occurred at Suining City whch is located the center of Sichuan Basin. It is unusual for the strong earthquake to occur at the center of Sichuan Basin with a stable geotectonic environment and a low-level historical seismicity. The macro-epicenter of the earthquake is located at Moxi town of Suining city, Sichuan province, China. The earthquake intensity of the epicenter area is degree Ⅶ, and the long axis of the isoseismal line trends in NE orientation. The Suining earthquake caused the collapse or destruction of 460 family houses. The earthquake focal mechanism solution and records of the near-field seismographic stations showed the earthquake occurred at the reverse fault at a depth 3-4 km. Based on the waveform and focal mechanism, we consider the Suning earthquake is triggered by the reverse fault and not by the gravitational collapse or man-made explosive sources. Basing on seismic refraction profile and borehole, we consider that the earthquake is triggered by the backthrust fault of Moxi anticline rooted in detachments at a depth 3-4 km.Furthermore, we infer that tectonic mechanism of the Suining (Ms5.0) Earthquake is driven by the horizontal crustal shortening and stress adjustment on a shallow detachment after the Wenchuan (Ms 8.0) earthquake.