Geometric Controls on Splay Fault Nucleation: 3D Finite-Element Modeling of the 2023 Mw 7.8 Kahramanmaraş Earthquake

Abstract Why splay faults in continental transform fault systems rupture preferentially during strike-slip earthquakes remains an open question. Deciphering the underlying mechanism could enhance the understanding of earthquake physics and seismic hazards. Here, we investigate the 2023 Mw 7.8 Kahramanmaraş earthquake using a simplified 3D elastic–plastic finite-element model to test how fault geometry influences nucleation. Our results show that depth-dependent curvature of the Nurdağı fault (NF; i.e., listric geometry with decreasing dip at depth) leads to nonlinear redistribution of stresses within the East Anatolian fault zone system. This geometry lowers the instability threshold of the splay fault and promotes earlier nucleation compared with planar configurations. When boundary conditions are calibrated to reproduce the average ∼6 m coseismic slip of the 2023 event, the listric case yields slip distributions and hanging-wall subsidence patterns that are more consistent with seismic and geodetic observations than planar models. These findings do not establish that the NF is definitively listric, but they demonstrate that if it has such curvature, nucleation is preferentially promoted on the splay fault, providing a plausible mechanical explanation for the observed rupture initiation.