LAUSR

Abstract The appearance of the surface rupture of the NW-striking Xiaoyudong Fault during the Wenchuan earthquake has attracted attentions of scholars and subsequently aroused debates about it. The size and tectonic significance of this fault is the key of the debates. Based on maps of gravity and magnetic in the scale of 1:500,000, the wavelet multi-scale method and the power spectrum method were used to obtain the wavelet fault analysis maps at different scales with average field source depths. Furthermore, the Euler deconvolution solutions of magnetic were determined and a simple model of the crust was built through the joint inversion of gravity and aeromagnetic data to analyze the penetration depth of the Xiaoyudong Fault. Combining these data with aftershock relocation data of Wenchuan earthquake provides better understanding of the Xiaoyudong Fault. We found that the Xiaoyudong Fault strikes NW cutting through the Pengguan and Xuelongbao complexes, and extending to the Yibasan area of Dazhou in Sichuan Province. The total length of the Xiaoyudong Fault is estimated to be 100 km, and its depth of penetration is less than 20 km, indicative of the Xiaoyudong Fault as a part of the decollement structural system. The parallel Miyaluo Fault is on the west of the Xiaoyudong Fault, cuts to a depth of less than 20 km, and is also a part of the same decollement structural system. The Xiaoyudong and Miyaluo faults are both part of the NW-striking tectonic system in the Songpan–Ganzi Fold Belt. The Xiaoyudong Fault was active during the Mesozoic and was reactivated during the earthquake with the Longmenshan Fault Belt under the present tectonic stress regime. However, only the southern most part of the Xiaoyudong Fault ruptured at the ground surface in the Wenchuan earthquake.