Deep Azimuthal Seismic Anisotropy in the Westernanatolia and Aegean Subduction Zone

Shear wave splitting due to source-side mantle anisotropy is estimated from broadband teleseismic and local S waves using a suite of Aegean subduction zone events. The data have been recorded by Kandilli Observatory and Earthquake Research Institute (KOERI) stations, at the depth of more than 30 km, from 2000 to 2007. We assume that there are at most two anisotropic regions along the ray path: one on the source-side and the other one on the receiver-side. It has been known that receiver-side splitting is found from analysis of SKS waves. Aim of this study is to investigate the kinematics of subduction; its influence on mantle convection and related deformation by using seismic anisotropy. From the combined analysis of SKS, local S, and teleseismic S waves, we have concluded that there must be azimuthal seismic anisotropy in the deep part of the mantle around the consuming slab. The splittings of the waves recorded at the stations in the western Anatolia have allowed us to constrain the orientation and depth distribution of the anisotropy both below and above the slab. In the lithospheric mantle beneath the western part of the Anatolia, Swave fast propagation direction is parallel to the direction of the extension of the Aegean region. Our results at Balıkesir (BALB), Antalya (ANTB) and Dalyan (DALT) stations show that fast split shear wave direction is about NE and delay time greater than 1 sec. These findings give information about the nature of the deformation and the coupling between the subducted lithosphere and surrounding asthenosphere. These results are consistent with the presence of azimuthal seismic anisotropy in the asthenosphere below the slab. Local S phases recorded at Southern Aegean Region (SAR) stations, yield fast directions that are not similar to the pattern of the SKS results at the depth of 133 km. We have found high delay times among the S phases in this region (SAR). This situation can be explained with the important coupling between cold slab and the intense mantle convection.