Preliminary Analysis and Model of the Complex Rupture Dynamics Behind the Mw 7.8 and Mw 7.5 Kahramanmaraş Earthquakes in Türkiye

The Kahramanmaraş seismic sequence has involved several segments of the East Anatolian fault system in Turkiye with two Mw > 7 earthquakes and widespread aftershock activity. Its spatial and temporal evolution showcases strong interactions among different fault patches. We characterize such complexity by focusing on the dynamics of 6th February 2023 Mw 7.8 Nurdagi mainshock (occurred at 4:17 am local time) and the Mw 7.5 Elbistan event, which followed about nine hours later, and their relationship with early aftershock activity. We show that the first event, after breaking a lateral fault with low rupture velocity, triggered a cascading instability on the main fault with at least two dynamic transfers from one patch to another, producing bilateral rupture with high rupture velocity. Sub-events are detected and relocated by analysing the frequency content and arrival times of accelerometric seismograms recorded by the AFAD and KOERI stations. We model the expected variations of rupture velocity based on the rheological variability of rock volumes and local stress drop during faulting. Rupture velocity turns out to be positively correlated with shear strength and negatively related to local stress drop and early aftershock rate. Our results provide a qualitative explanation of the observed complex dynamics of the main event and following seismic activity. We also notice that the same framework can be applied to cascade ruptures to explain why large strike-slip faulting events are featured by a significantly higher probability of fast rupture velocity, even super-shear as it occurred with the second Mw 7.5 mainshock, than in contractional and extensional faulting styles. Our findings also suggest a role for almost instantaneous event triggering in enhancing ongoing ruptures, producing substantial limitation for the prediction horizon of seismic events.