Numerical Modeling of Interactions between Shallow and Deep Faults in the North China Plain: Insights from the Sanhe-Pinggu Seismic Zone

Several strong seismic zones in the North China Plain (NCP) share common structural characteristics between deep and shallow seismogenic faults. However, stress interaction or coupling mechanisms between these deep and shallow faults remain unclear. This study examines the Sanhe-Pinggu seismic zone, a representative strong seismic belt in the NCP, using newly acquired data from deep reflection profiles, geological surveys, and geodetic measurements. A 3D viscoelastoplastic finite element model was developed to represent the study area, integrating both deep and shallow seismogenic faults. Through quasi-static geodynamic simulations of stress loading and plastic sliding along pre-existing faults, this model explores the stress-strain evolution of faults under various tectonic loading conditions, revealing the long-term interaction between deep and shallow faults. Results indicate that the stress coupling and interactions between deep and shallow faults are significantly influenced by boundary loading conditions, the depth and presence of detachment layers, and rapid creep along deeper faults. These findings provide critical insights into fault interaction and the mechanism of strong earthquake generation within the NCP.