Source Parameters and Ground-Motion Simulation of the 2023 Mw 5.5 Pingyuan Earthquake in the North China Plain

Abstract The North China Plain (NCP) is a tectonically active region that has experienced several devastating earthquakes over the last century. However, its seismic activity has been relatively low for nearly half a century since the 1976 Mw 7.6 and 7.0 Tangshan earthquakes. In August 2023, an Mw 5.5 earthquake struck Pingyuan County, Shandong Province. It was the largest earthquake in the NCP in the last 40 yr and resulted in unexpected ground shaking. This event was well recorded by local strong-motion accelerometers and regional broadband seismometers, providing a valuable opportunity to investigate its seismogenesis and assess seismic hazards in the NCP. In this study, we determine the source parameters of the Mw 5.5 Pingyuan earthquake and investigate the effects of unconsolidated sediments on ground motions. Using the Cut-And-Paste inversion and depth-phase waveform modeling methods, we accurately determine the focal mechanism and depth of the earthquake. Our results indicate right-lateral strike-slip motion on a deep-seated fault with a focal depth of 17 km. Ground-motion simulations, based on the determined source parameters and a detailed 3D velocity model, reveal significant ground-motion amplification in sedimentary basins, correlating with the thickness of unconsolidated sediments. Our study underscores the importance of subsurface structures in ground-motion prediction and seismic hazard assessment, particularly in the context of future large earthquakes in the NCP.