Preliminary Investigating results from Azimuthal Seismic Anisotropy beneath Western Anatolia and the Hellenic Subduction Zone

Authors : Gülten Polat, Nurcan Meral Özer, Stuart Crumpin

Pages : 229-240

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Publication Date : 2017-12-03

Article Type : Research

Abstract :To understand the dynamics of a subduction zone, seismic anisotropy is often used, despite the difficulty of constraining anisotropy in the sub-slab region. However, particularly due to constraints imposed by deformation patterns in the mantle surrounding subducting slabs, seismic anisotropy is usually chosen as a better tool. In this study, the dynamics and kinematics of the Hellenic subduction zone and its impact on mantle convection related deformation are investigated by using source-side seismic anisotropy. To this aim, shear wave splitting parameters of local and teleseismic S waves from intermediate and shallow earthquakes are measured. Then, they are combined with splitting parameters obtained from teleseismic SKS and SKKS waves in order to determine variations in seismic anisotropy with depth. Although in the study area strong deep earthquakes are not available, our preliminary splitting results are quite reliable. Also, they are fairly consistent with the presence of azimuthal seismic anisotropy in the asthenosphere below the slab. The averaged fast polarization directions obtained from the analysed teleseismic events show N-S orientations. Additionally, we observed that S-wave fast polarization directions are nearly parallel to the present extension direction of Western Anatolia. It might be suggested that anisotropy may localize within the lower crust, but does not appear to be associated with the present lithospheric extension. Average delay time of teleseismic SKS is greater than 1 s.
Keywords : kaynak-yanı anizotropi, kesme dalgası ayrımlanması, yitim zonu, Ege bölgesi