Kinematics of the Western Makran Subduction Zone: Insights From InSAR Analysis of Interseismic Coupling

Subduction zones are key in shaping seismic hazards, yet many remain poorly understood. The Western Makran Subduction Zone (WMSZ) is a good example of a challenging hazard assessment due to its low seismic activity and limited geodetic data. The motivation is to explore the feasibility of using recently available long InSAR time-series to estimate low-amplitude interseismic behavior of such challenging areas. Through a sensitivity analysis, we demonstrate that with proper atmospheric signal mitigation, Sentinel-1 time-series can isolate the interseismic deformation in WMSZ. Building on this, we develop an InSAR time-series method focused on reducing atmospheric errors. Using corrected data, we propose inverse modeling without inserting rigid smoothing constraints, improving model flexibility to capture localized variation in coupling distribution. Results reveal the presence of partial coupling down-dip, contrary to previous studies. Near the coast, coupling values range from weak to moderate (0.3–0.6), dropping to near zero at around 25 km depth, and increasing partially at 30 km depth. The location of the observed partial coupling coincides with previous moderate seismic activities and the $M_w$ 5.1, 5 March 2024 (Fanuj) earthquake. Comparison with GPS measurements shows similar deformation rates, validating the obtained results. The results indicate the possibility of partial coupling in intermediate depths under the southern Jazmourian plain, increasing the potential of moderate seismic hazard in WMSZ. This experience demonstrates that InSAR's high spatial resolution, combined with advanced error mitigation and slip modeling, can effectively capture small interseismic deformations even in subduction zones with low seismic activity.