SHEAR WAVE SPLITTING MEASUREMENTS BENEATH IRANIAN PLATEAU

Recordings of teleseismic events from 76 three-component stations deployed over the Iranian Plateau were used for shear wave splitting studies. No significant splitting was observed in Zagros, Alborz, Kopet-Dagh and NW Iran suggesting the absence of any coherent anisotropic fabric into the upper mantle beneath these regions. On the other hand, time lags greater than 0.8 sec with a general NW-SE fast polarization direction were observed in a narrow zone in Central Iran. Inhomogeneous splitting pattern over the Iranian Plateau precludes mantle shearing induced by present-day absolute motion of the Plateau to cause the observed shear wave splitting. Neither, the observed splitting pattern beneath Iran is related to the current crustal deformation. Rather, we suggest that the observed splitting in Central Iran is due to some inherited anisotropy in the lithosphere related to a coherent fabric acquired during a previous tectonic episode, namely during the continental rifting in the early Mesozoic or oceanic subduction in the middle to late Mesozoic.

کلیدواژه ها:

Iran ، shear wave splitting ، seismic anisotropy ، SKS waves ، upper mantle structure