Bayesian inference of interseismic coupling along the East Anatolian Fault using geodetic data

Historically, the East Anatolian Fault Zone (EAFZ) has regularly produced M_W ~ 7 earthquakes, but has also occasionally ruptured in M_W ~ 8 events. After a century without any significant earthquake, the M_W 6.8 Elazığ (24 Jan. 2020), M_W 7.8 and M_W 7.6 Kahramanmaraş (6 Feb. 2023) events occured in a new sequence of major earthquakes. Understanding the recurrence pattern of earthquakes in this complex fault network, as well as assessing seismic hazard and strain accumulation in the region, requires careful estimation of the spatial distribution of interseismic coupling (defined as the degree of locking of a fault between earthquakes) along the EAFZ. Previous attempts focus on restricted segments of the fault system or did not include all available geodetic data.

We use GNSS and InSAR interseismic velocity fields to derive a map of interseismic coupling along the EAFZ applying the linear elastic block modelling framework. The GNSS velocity field is a combination of previous compilations (Ergintav et al., 2023; Özbey et al., 2024). We obtained InSAR velocities by postprocessing time series computed by the FLATSIM initiative (Thollard et al., 2021), to remove coseismic signals and seasonal oscillations. We use a Bayesian approach to invert for interseismic coupling to carefully quantify associated uncertainties and assess the minimum complexity required for the block model.

We find that eastern Anatolia mostly behaves as a unique block with slip rates standing out of uncertainties for a limited number of identified active faults. The portions of the EAFZ that ruptured during the Elazığ and Kahramanmaraş earthquakes are strongly locked during the interseismic period, as expected. The inferred locked asperities are also consistent with evidence for large historical earthquakes. To the north, the EAFZ is mostly weakly coupled and exhibits shallow creeping segments that delimit the northern boundaries of the 2020 and 2023 ruptures. As creeping segments may be related to the initiation and termination of seismic ruptures, it is crucial to estimate these sections precisely to fully assess the earthquake potential of a fault.