Seismic anisotropy structure beneath the southeastern Mediterranean from shear-wave splitting

Abstract

Analysis of seismic anisotropy in the crust and the uppermost mantle gives lots of information about the ambient mantle flow, stress state, and the dynamic processes inside the Earth. Thus, seismic anisotropy and its main distinctive features beneath the southeastern Mediterranean region are studied through the analysis of teleseismic shear-wave splitting observed at six broadband seismic stations belonging to the GEOFON and the MedNet. Although the number of the recording stations is small; a total of 495 splitting parameters are obtained, which revealed significant variations in the observed fast polarization directions beneath the study area. The stations in northern Egypt and Cyprus show fast velocity directions oriented roughly N–S to NNE–SSW, coincident with many previous results. A slightly different splitting pattern comprising NE–SW fast polarization directions is observed in the stations located along the Dead Sea fault in the southeastern Mediterranean; which are consistent with the current strike-slip motion between Africa and Arabia. In addition, NW–SE fast polarization directions are recognized in the latter group. The observed delay times vary greatly but their averages lie between 0.35 and 1 s. Although large-scale mechanisms, such as the absolute plate motion of Africa and Arabia towards Eurasia and the differential motion between Arabia and Africa can be invoked to predominantly explain the origin of anisotropic features, we suggest that density-driven flow in the asthenosphere is a possible additional cause of the wide range of the splitting pattern observed beneath some stations.