Seismic anisotropy along the Cyprean arc and northeast Mediterranean Sea inferred from shear wave splitting analysis

Yolsal-Cevikbilen S.

PHYSICS OF THE EARTH AND PLANETARY INTERIORS, vol.233, pp.112-134, 2014 (SCI-Expanded) identifier identifier


The Cyprean arc is considered to be a convergent boundary in the Eastern Mediterranean where the African plate is being subducted beneath the Anatolian plate. Mapping the lateral variations of seismic anisotropy parameters can provide essential hints to mantle dynamics and flow patterns in relation to the geometry and style of deformation developed under different pressure, temperature conditions around the subducting African lithosphere. In this study, seismic anisotropy parameters, fast polarization directions (phi) and delay times (delta t) beneath the Cyprean arc and NE Mediterranean Sea are inferred from the shear wave splitting analysis performed on core-mantle refracted teleseismic shear waves (SKS phases). Earthquake data used in the present work are extracted from the continuous recordings of 8 broad-band seismic stations located in the study region for a time period during 1999 and 2012. The overall results exhibits clear evidences of mantle anisotropy with relatively uniform NE-SW aligned fast polarization directions. No abrupt changes in fast polarization directions (phi) are observed. However, near the Dead Sea Transform Fault, phi values tend to rotate from NE-SW to N-S and NW-SE in accordance with P. anisotropy observations. Delay times (delta t) vary between 0.61 s +/- 0.10 s and 1.90 s +/- 0.13 s. The range of delay times are generally consistent with those observed in the mantle rather than implying a crustal anisotropy. A predominant pattern of NNE-SSW fast polarization directions that is coherent with earlier SKS splitting measurements observed beneath north, central and East Anatolia suggests a SW directed asthenospheric flow caused by slab rollback process along the Hellenic and Cyprean arcs. Furthermore, apparent splitting parameters did not exhibit any significant directional dependence which may imply possibility of the presence of anisotropic models with two-layer anisotropy or dipping axis of symmetry beneath the northeast Mediterranean Sea and Cyprean arc. Consequently, a simple, single-layered and sub-horizontal anisotropy model is tentatively suggested for the study region. (C) 2014 Elsevier B.V. All rights reserved.