Seismological analysis of the tectonic evolution of the Laji Shan fault from the 2023 Jishishan MS 6.2 earthquake

The 2023 Gansu Jishishan MS 6.2 earthquake provides seismological evidence for investigating the origin and evolution of the Lajishan fault zone. To better understand the connection between this tectonic evolution and the resulting seismic hazards, this study reconstructs the rupture process through dynamic simulations, focusing on the mechanism behind the weak deformation–high intensity surface features. The results show that the rupture front propagated mainly northwestward and down-dip along the fault plane. This led to concentrated energy release in the down-dip direction, which enhanced long-period energy components, affected the response of high-rise buildings, and generated stronger ground motions in the deeper fault segments and far-field regions. The weak deformation–high intensity phenomenon was primarily caused by the combined effects of the hanging-wall effect, sedimentary layers in the source region, the basin edge effect, and the internal amplification of seismic wave focusing. Furthermore, the rupture process was constrained by faults and structural features formed during the tectonic evolution of the Lajishan fault zone, indicating that long-term tectonic development governed the geometry of the seismogenic fault and rupture characteristics of this earthquake.