Bayesian Co- and Postseismic Slip Model of the 2023 Mw 7.8 and 7.7 Türkiye–Syria Earthquake Doublet from Geodetic Data

On 6 February 2023, an earthquake doublet occurred in the East Anatolian fault zone (EAFZ), producing significant surface displacements and causing extensive damage in Türkiye and Syria. The EAFZ is known to be spatially complex, with multiple segments, fault stepovers, and fault-bend structures. How such fault complexities modulate the co- and postseismic distribution of fault slip remains an important question. We use Sentinel-1 and Advanced Land Observation Satellite-2 Synthetic Aperture Radar-derived pixel offset measurements and Global Navigation Satellite Systems (GNSS) static offsets for the two events to constrain the distribution of coseismic slip along both strands of the EAFZ. We constrain the postseismic slip distribution using Sentinel-1 interferograms and GNSS time series. We adopt a Bayesian framework to explore the solution space, relying solely on physically justifiable prior information without employing artificial regularization. We account for both observational errors and epistemic uncertainties due to imperfect knowledge of the regional elastic structure and orientation of the fault plane. We find that elastic afterslip mostly surrounds the areas of coseismic rupture. However, the geodetic data sets that span the postseismic period cannot be explained solely by elastic afterslip. We also confirm the potential seismic gap on the boundary between the Erkenek and Pütürge faults, across which neither coseismic nor postseismic slip occurs in the periods considered here.