The Role of Fault Geometry in the Size of the 2023 Kahramanmaraş Earthquake Doublet

Abstract

The multi‐segment ruptures of the 2023 MW ${M}_{W}$ 7.8 and MW ${M}_{W}$ 7.6 Kahramanmaraş earthquakes caused extensive deformation across the entire width of the East Anatolian Fault Zone (Türkiye). To understand how this earthquake doublet could affect such a large region, we model coseismic slip for both earthquakes using surface deformation measurements. We use a Bayesian framework to obtain uncertainties and constrain the significance of our findings. Our model suggests that most of the coseismic slip distributes above 20 km depth with a shallow slip deficit ratio varying along strike from 10% to 80%. Slip is segmented along strike, with higher values on relatively straight segments and decreases at geometric complexities. We also construct postseismic InSAR displacement time series and find that segments with the most afterslip are located at the northeastern end of both ruptures. Aftershocks are usually located along the fault planes, except at the southwestern tip of both ruptures where they spread in wide fan‐shaped zones. These observations can be related to the relative geometric complexity of the southwestern termination of both earthquakes, where extensive crustal damage could have stopped the rupture. Finally, by visualizing the localization of interseismic deformation, we depict the role of strain partitioning between subparallel strike‐slip faults in the unusually large spatial extent of the Kahramanmaraş doublet. These findings highlight the seismic hazard posed by similar tectonic structures in other broad plate boundaries.