High-angle fault responsible for the surface ruptures along the northern segment of the Wenchuan Earthquake Fault Zone: Evidence from the latest seismic reflection profiles

Abstract

The inverse/right-lateral Yingxiu–Beichuan fault ruptured during the Wenchuan earthquake for ~270 km. We investigated the northeastern segment of that fault by analysing 3 newly acquired and 3 older seismic lines that cross the fault. We combine this analysis with that of the surface ruptures and of the regional geology in order to discuss the geometry, the style and the amount of motion of the fault. We conclude that the Yingxiu– Beichuan fault is very steep (~70°) at the surface and has still a dip N 45° at 6 km depth. The fault offsets all pre- vious structures and particularlythe Tangwangzhainappesfrom which a verticaloffsetof3 to6 kmisevaluated. The right-lateral component of motion along the Yingxiu–Beichuan fault appears to be larger at the surface than at depth and increases only slightlytowards the NE.We suggest that the Yingxiu–Beichuan faultis continuous at depth between its northern and southern segments.