Characteristics on the fault behavior of the Longmen Shan fault zone by the co-seismic horizontal displacements given by the SPOT imagery for 2008 Wenchuan Earthquake

Two major parallel surface ruptures [i.e., the Beichuan-Yingxiu Fault (BYF) and Guanxian-Jiangyou Fault (GJF)] was produced by 2008 Wenchuan earthquake (Mw 7.9) and associated with previously published Longmenshan fault zone system. The strike of fault zone system is roughly along NE-SW and the ruptures extended to 240 km and 70 km for BYF and GJF respectively. Although, the filed observations at surface ruptures and DInSAR result had been published, the continuous surface displacements across BYF and GJF are not easy measured by other methods. The comparison of the SPOT imageries taken before and after earthquake can produce continuous ground displacements distributed in a large area by this study and make more constrain for the fault slips especially around GJY area. Across GJF, our results show the maximum normal and strike-slip offset could reach 4.5 m and 3.2 m respectively around Hanwang. Across BYF, the strike-slip offset could reach 6.7 m around Beichuan and the maximum normal offset could be larger than 7m around Guan Xian in the south and around Beichuan in the north. From Beichuan northward all the ground displacements slipped parallel to the fault, suggesting a pure strike-slip fault. Following the fault geometry published by Hubbard et al. (2010) with the GPS and our results, the much detailed fault slips could be inversed by Okada code. The two obvious asperities on BYF could be shown at southern area and Beichuan area. In addition, the local larger net-slips were shown around the northern part of GJF, and there were more strike-slips than dip-slips in the northern part of the BYF. Comparison with the secular rate from Shen et al. (2009), the recurrence interval might be more than thousand years, and the northern part should be longer than the southern part of BYF. Furthermore, the recurrence interval of GJF should also longer than of BYF.