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

Year 2017, Volume: 38 Issue: 3, 229 - 240, 03.12.2017

Gülten Polat , Nurcan Meral Özer Stuart Crumpın

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

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