Abstract: Surface rupture zone of Wenchuan earthquake(M8.0) on the Pengxian—Guanxian fault located between Cifeng and Suishui, the whole length was about 90 km where Bailu town located at southern part of surface rupture zone. The vertical offsets,horizontal offsets and tectonic shortening rate were measured precisely with total station instrument and GPS. The results showed that vertical offsets and horizontal offsets in Bailu town were most obvious along Pengxian—Guanxian fault, the largest slip amount was (2.7±0.2) m vertical offset in Bailu old street and (0.7±0.2) m horizontal offset in Bailu river embankment,Pengzhou. The were reasons were presented as follows: the coal seam in Bailu town was most abundant and most thick along Pengxian—Guanxian fault, the yield strength of soft rock was relatively low, and slippage of rock located both sides of fault was largest. Two branch faults which were imbricate arrangement were discriminated by the trial trench near Bailu middle school. Dip angle and change trend of dip angle with depth were consistent with the conclusion inferred by focal mechanism solution.

Key words: Wenchuan earthquake(M8.0), Pengxian—Guanxian fault, surface rupture, Bailu town, coseismic dislocation