Seismic Anisotropy Variations in the Eastern Mediterranean Sea Region Revealed by Splitting Intensity Tomography: Implications on Mantle Dynamics

Abstract

Reliable knowledge of seismic anisotropy in the mantle can provide invaluable insights into complex tectonics and geodynamics in Anatolia controlled by intricate plate interactions across the region. However, the 3D variations in seismic anisotropy within the crust and upper mantle beneath this area remain poorly constrained. In the present study, we performed splitting intensity (SI) tomography technique, using over 25,000 SI measurements from SKS/SKKS waves recorded at 690 seismic stations, to map lateral and vertical variation of anisotropy that is essential for accurate geodynamic interpretations for Eastern Mediterranean. Our tomographic images show large-scale mantle flow at asthenospheric depths, oriented in east-west and northeast-southwest directions. This flow pattern can be attributed to basal drag forces, which play an important role in driving the westward motion of the Anatolian plate. The strong azimuthal anisotropy in the back-arc region of the Hellenic subduction zone, with trench-perpendicular orientation, highlights the significant impact of trench retreat and rollback of the African lithosphere on deformations in the mantle lithosphere and asthenosphere beneath the Aegean region and western Türkiye. The observed weak azimuthal anisotropy, on the other hand, is largely identified across various depths beneath Quaternary volcanoes in the Central and East Anatolian Volcanic Provinces and along the Cyprus subducting slab in the upper mantle. Our numerical tests prove that these weak anomalies may result from plunging/vertical anisotropy associated with upwelling and/or downwelling mantle in central and eastern Anatolia.