Intraplate seismic mechanisms in the Zhangjiakou-Bohai Seismic Belt: insights from magnetotelluric data

Abstract The Zhangjiakou-Bohai Seismic Belt (ZBSB) is a crucial intraplate seismic belt in Eastern China, covering densely populated and economically developed regions with significant seismic hazards. A refined model is essential to investigate the intraplate seismic mechanism here. We obtained the three-dimensional resistivity model based on magnetotelluric array data covering the central segment of the ZBSB. The model shows a thick high-resistivity body within the Sanhe-Pinggu seismogenic zone and a widespread low-resistivity anomaly in the mid-lower crust east of the Xiadian fault. Moreover, the Tangshan seismogenic zone exhibits a highly resistive layer in the mid-upper crust and a high-conductivity anomaly from the lower crust to the upper mantle west of the Tangshan fault. The ZBSB is primarily affected by mantle thermal material migration from the west and mantle material upwelling in the central segment of the ZBSB. In the central-western sections, the horizontal eastward push, caused by the migration of mantle thermal material from the west, accumulates stress within the rigid blocks in the Sanhe-Pinggu seismogenic zone, leading to strike-slip and rupture along the Xiadian fault. The ductile mid-lower crust on the east side of the Xiadian fault unloads stress from the rigid body, hindering eastward stress transmission. In the central-eastern segments, seismic events are mainly triggered by mantle-derived material upwelling. The NE horizontal stress exerted on the rigid body of the Tangshan seismogenic zone, resulting in strike-slip and rupture along the brittle Tangshan fault, leading to earthquakes. Graphical Abstract