Characteristics of Distributed Deformation in the 2023 Turkey Earthquake Doublet Fault Zone Revealed by Optical Geodesy

Co-seismic deformation in fault damage zones manifests as a combination of localized slip and distributed deformation. Accurately quantifying the ratio between these two components is essential for understanding displacement partitioning and assessing near-fault seismic damage. Focusing on the widespread ruptures caused by the 2023 Turkey-Syria earthquake doublet (Mw 7.8 and Mw 7.6), this study utilizes optical satellite geodesy to dissect the deformation characteristics of the East Anatolian Fault Zone. We integrated high-resolution GaoFen-7 orthophotos (0.8 m) and Sentinel-2 imagery to distinguish between on-fault and off-fault deformation. Localized slip was measured by tracing displaced linear markers (e.g., roads, ridges), while the total horizontal displacement field was reconstructed using optical displacement tracking. By comparing total displacement across dense profiles against localized slip, we isolated the distributed component. Results show that for the Mw 7.8 event, 80% of displacement was localized, with 20% distributed across a 203-meter-wide zone. Similarly, the Mw 7.6 event exhibited 17% distributed deformation within a 141-meter-wide zone. Notably, we observe that the spatial heterogeneity of deformation is strongly controlled by the pre-existing geometric complexity of the fault system. These findings provide critical constraints for fault displacement hazard models.