Abstract:

Abstract:  On May 12th, 2008, a great Ms 8.0 earthquake occurred in Wenchuan County, Sichuan Province. The BeichuanYingxiu fault extending about 220 km characterized by dextral strikeslip  faulting is one of the three main seismogenic faults along the Longmenshan Fault zone,  and its activity is much more important than the other two. The major shock had induced  clear striations presenting at some local places along  the rupture of the BeichuanYingxiu fault,  the location and size of the striations may  be the surface response to  the peak value of  the deep rupture. Based on the stress field reflected by the striations and on the  relationship between displacement and surface rupture length,  the BeichuanYingxiu rupture zone are able to be subdivided into three segments, namely the Hongkou subsection,  the Beichuan subsection and  the Nanba subsection. Among them, Hongkou subsection extends 2245 km, with coseismic displacement of 4.5 m with  σ1 stress in the direction of NWWNW,  which had undergone at least three phases of activation. It is indicated that  the phase Ⅲ is the most intensive reverse faulting which reconstructs the phaseⅠandⅡ dextral strike slip activity, which all  are controlled by the main shock. The Beichuan subsection extends 90100 km, with coseismic displacement of 3.5 m, and σ1 stress  in the direction of NWW and is approximately horizontal,  and its intensity is weaker than the phase III of Hongkou . The Nanba subsection extends 3550 km, with coseismic displacement of 2.5 m and  σ1  stress  in the direction of NWW characterized by nearly horizontal compression. The  σ1  azimuth is 180°different from those of  the south and middle segments,  and its intensity is similar to that of the phaseⅠandⅡ of the south segment.

Key words:

Key words: Wenchuan county; Ms 8.0 earthquake; striation; fault subsection