Super-shear ruptures steered by pre-stress heterogeneities during the 2023 Kahramanmaraş earthquake doublet

The 2023 M7.8 and M7.5 earthquake doublet near Kahramanmaraş, Turkey, provides insight into how large earthquakes rupture complex faults. We determine the fault geometry using surface ruptures and Synthetic Aperture Radar measurements, and rupture kinematics from joint inversion of high-rate GNSS, strong-motion waveforms, and GNSS static displacement. The M7.8 event initiated on a splay fault and subsequently propagated along the main East Anatolian Fault with an average rupture velocity between 3.0 and 4.0 km/s. In contrast, the M7.5 event exhibited bilateral supershear rupture of about 5.0–6.0 km/s over an ~80 km length. Despite varying strike and dip angles, the sub-faults involved in the mainshock are nearly optimally oriented relative to the local stress tensor. The second event ruptured a fault misaligned with respect to the regional stress, pointing to local stress heterogeneity and a possible free-surface effect.