Seismic anisotropy under Zagros foreland from SKS splitting observations

Abstract

We present SK[K]S splitting measurements from 18 newly deployed seismic stations in the foreland of the Zagros collision zone, providing new insights into asthenospheric flow and lithospheric deformation associated with the Arabian-Eurasian continental collision. Our results reveal two distinct fast-axis orientations: NE–SW in northern Iraq and NW–SE in the Mesopotamian Plain and Persian Gulf. The NE–SW anisotropy in northern Iraq aligns with fast-axis orientations observed in the Iranian-Anatolian Plateau and the azimuth of absolute plate motion, indicating large-scale asthenospheric flow as the primary cause of anisotropy across the northern Middle East. In contrast, the NW–SE-trending anisotropy in the Mesopotamian Plain and Persian Gulf, characterized by smaller splitting times, is parallel to the previously reported Pn anisotropy, suggesting a contribution from lithospheric mantle anisotropy, likely preserved as a remnant of past rifting. The influence of asthenospheric flow on the observed seismic anisotropy in this region appears minor. These findings demonstrate a dual origin of seismic anisotropy in the Zagros foreland, where lithospheric fabric related to Mesozoic rifting dominates in the Mesopotamian Plain, southwest of the Zagros lithosphere keel, while asthenospheric flow governs the anisotropy in northern Iraq and surrounding regions with thin lithosphere. This distinction refines models of mantle dynamics and lithosphere-asthenosphere coupling in continental collision zones.