Late Cenozoic paleostress reconstruction and stress regimes in Taiyuan basin of the Shanxi rift, North China

摘要

The Taiyuan basin, initiated during the late Cenozoic, is part of the left-stepping en-echelon graben systems of Shanxi. The state of stress in this area and its evolution over time is a significant concern given the existence of high shear strain and seismic risk along the basin boundary faults. In the present study, the inversion of fault-slip data through the right dihedron and the rotational optimization methods led us to identify 21 significant paleostress tensors. The maximum principal stress orientation shows two modes trending NE-SW and ENE-WSW with most of stress tensors having stress ratio values within a wrench regime. The extensional sites reveal NW-SE and NE-SW directions. Three tectonic stages with different kinematics were successfully identified since the late Cenozoic. The oldest event has been identified in our analysis since the late Miocene to late Pliocene and belongs to NW-SE extension/strike-slip stress regime. The next was generated in the early Pleistocene under the NE-SW extension stress regime, and the youngest activity recorded belongs to the NNW-SSE extension/strike-slip regime developed since the late Pleistocene. These events were dynamically driven by the northeastward extrusion of the Tibetan Plateau in response to the plate boundary motion involving the Indian and Eurasian plates and lesser by the NW subduction of the Pacific plate. The present-day stress state is characterized by ENE-WSW compression and NNW-SSE extension derived from earthquake focal mechanisms.