Off-fault damage and deformation triggered by the 2023 Kahramanmaraş earthquake doublet revealed by InSAR time series

The 2023 Mw 7.8 and Mw 7.6 Kahramanmaraş earthquake doublet produced complex deformation patterns across southeastern Turkey, offering a rare opportunity to investigate the response of non-main fault structures to large strike-slip earthquakes. Using time-series Interferometric Synthetic Aperture Radar (TS-InSAR) analysis, we quantify both coseismic and postseismic deformation in the epicentral region, with a particular focus on off-fault structures that were previously considered inactive. Our results reveal that, beyond the primary rupture zones, several off-faults exhibit significant postseismic deformation characterized by increased deformation rates, indicating fault reactivation rather than residual coseismic effects. To explore the driving mechanisms of this off-fault activation, we compare the observed deformation patterns with modeled static Coulomb stress changes and dynamic stress perturbations associated with the earthquake doublet. The spatial distribution of activated off-faults shows a strong correlation with areas experiencing positive Coulomb stress changes and regions affected by strong dynamic shaking. Temporally, the deformation signals display heterogeneous behavior, ranging from rapid early postseismic transients to sustained deformation persisting for months to years after the mainshocks. These observations suggest that the combined effects of static and dynamic stress transfer played a key role in triggering off-fault deformation following the Kahramanmaraş earthquakes. Our study highlights the importance of off-fault structures in accommodating postseismic strain and emphasizes their potential contribution to regional seismic hazard, which is commonly underestimated in traditional fault-based assessments.