干旱区生态环境知识资源中心

Shear waveforms from core-refracted (SKS) phases recorded at 105 portable stations belonging to the DESERT and DESIRE campaigns and nine permanent broadband stations of the Israel Seismological Network are analyzed to study polarization seismic anisotropy beneath the region of the Dead Sea Transform fault in the Middle East. Shear wave splitting parameters exhibit variations with back azimuth (initial polarization) of the incoming SKS waves. The pattern of this variation is nearly constant along the strike of the fault suggesting a laterally uniform anisotropic structure beneath the Dead Sea region. The modeling of the azimuthal variations of the shear wave splitting parameters and split waveforms yields two-layered anisotropic models consisting of an upper layer with nearly N-S symmetry axis and a deeper layer with around N25 degrees E symmetry axis. The split time is almost equally partitioned between the upper and lower layers allotting a value of 0.6-0.8 s to each layer. 2-D finite difference modeling across the southern segment of the Dead Sea Transform fault demonstrates that anisotropic structure in the strike-normal direction is relatively uniform. The Dead Sea Transform fault appears not to have a significant role in the development of the regional anisotropic fabric. The upper anisotropic layer is possibly related to a fossil fabric in the lithosphere, inherited from the Precambrian Pan-African Orogeny. The lower layer may be related to the mantle deformation due to the relative motion between the lithospheric plates and the asthenosphere and possibly affected by the local flow field due to mantle plumes as inferred by other studies.