Summer shakes and winter loading: Seasonal earthquake occurrences along the Arabian Gulf

This study investigates the possible seasonal modulation of large earthquakes ( M w ≥ 6.0) in the Arabian Gulf and Zagros fold-and-thrust belt by atmospheric and terrestrial water storage (TWS) loading. By merging and rigorously declustering international catalogues, we isolated 34 independent mainshocks. Statistical analyses, including the Schuster test ( p = 0.06) and bootstrap resampling, suggest temporal clustering, with over 41% of events occurring during the summer months (July–September). In contrast, GRACE and ERA5 datasets reveal a synchronous winter peak in combined TWS and atmospheric mass loads of approximately 40 hPa. Coulomb Failure Stress (ΔCFS) modeling demonstrates that this winter load exerts a clamping effect on regional reverse faults. Conversely, rapid summer unloading reduces vertical confining stress, effectively unclamping the faults and increasing differential stress. While this geomechanical elastic-loading model provides a plausible physical mechanism that is temporally consistent with the summer seismicity peak, we distinguish this statistical correlation from definitive causation. Given the limitations of a small sample size and normal background tectonic variability, we conclude that seasonal surface unloading may modulate the timing of large earthquakes in the region, rather than acting as a definitive primary tectonic trigger.