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 34 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.

A catastrophic debris flow in the Wenchuan Earthquake area,July 2013：characteristics,formation,and risk reduction

In the Wenchuan Earthquake area,many co-seismic landslides formed blocking-dams in debris flow channels. This blocking and bursting of landslide dams amplifies the debris flow scale and results in severe catastrophes. The catastrophic debris flow that occurred in Qipan gully(Wenchuan,Southwest China) on July 11,2013 was caused by intense rainfall and upstream cascading bursting of landslide dams. To gain an understanding of the processes of dam bursting and subsequent debris flow scale amplification effect,we attempted to estimate the bursting debris flow peak discharges along the main gully and analyzed the scale amplification process. The results showed that the antecedent and triggering rainfalls for 11 July debris flow event were 88.0 mm and 21.6 mm,respectively. The event highlights the fact that lower rainfall intensity can trigger debris flows after the earthquake. Calculations of the debris flow peak discharge showed that the peak discharges after the dams-bursting were 1.17–1.69 times greater than the upstream peak discharge. The peak discharge at the gully outlet reached 2553 m^3/s which was amplified by 4.76 times in comparison with the initial peak discharge in the upstream. To mitigate debris flow disasters,a new drainage channel with a trapezoidal V-shaped cross section was proposed. The characteristic lengths(h1 and h2) under optimal hydraulic conditions were calculated as 4.50 m and 0.90 m,respectively.