Late Pliocene oblique thrusting and regional stress field changes in southern Longmen Mountain, eastern Tibet

摘要: The co-seismic slip sense of the 2008 Wenchuan earthquake (Mw 7.9) has demonstrated the present east-west (EW) crustal shortening and oblique thrusting across the Longmen Mountain. However, the oblique thrusting and its initial time remain poorly investigated. By using 3-D seismic reflection data, field investigation, and published dating results, the authors investigated the EW crustal shortening in the Dayi Fault System (DYFS), and determined tectonic stress field changes during the Late Cenozoic. Two-period tectonic deformations were found in the DYFS, which correspond to the NE-and NS-trending structures, respectively. The activities of the DYFS and Qiongxi Fault System reflect a change in the direction of the tectonic stress, from NW-SE during the Oligocene and Early Pliocene to EW from the Late Pliocene to Holocene. The 120km NS-trending structures in the southern Longmen Mountain range front as well as the Wenchuan earthquake co-seismic ruptures are assumed to reflect the active, EW crustal shortening in Longmen Mountain, eastern Tibet plateau. The results obtained by the authors provide a new perspective for the uplift mechanisms of eastern margin of the Tibetan Plateau.