a-Before generation；b-In generation；c-Co-seismism Causative mechanism and related tectonic movement of the 2008 Wenchuan M8 Earthquake

Abstract：In this study, seismicity background, stress fields, seismogenic tectonics and dynamics for the 2008 Wenchuan M8 Earthquake were investigated employing earthquake focal mechanisms, source fault parameters and coseismic displacements from GPS. The results suggest that the 2008 Wenchuan M8 event occurred under the tectonical motion in and around the Qinghai-Tibet plateau during a seismically active period since 2001. The Wenchuan M8 event with the 300 km long earthquake fault occurred on the eastern edge of the Qinghai-Tibet plateau, which filled the seismicity gap zone lacking M8 event from 1990. The eastward extensional motions of the Tibetan plateau and the counter action constitute the main tectonic property. The M8 Wenchuan event and its strong aftershocks occurred under a seismogenic stress field where P-axes align stably in NWW-SEE direction. It implies that the seismogenic stress field for the Wenchuan M8 event is mainly attributable to the actions of the stress fields lying on the southern segment of NSSB, the Shichuan basin and the South China block. The results from the source fault parameters and coseismic displacements from GPS suggest that the tectonic movement of the up-eastward slip of the Qinghai-Tibet plateau on the western side of the Longmen Mountain and the relative down-westward slip of the Sichuan basin might have been the causative mechanism of the 2008 Wenchuan M8 event.