LITHOSPHERIC DEFORMATION OF NE IRAN INFERRED FROM SHEAR WAVE SPLITTING

We have made measurements of seismic anisotropy beneath NE Iran performed on 43 teleseismic earthquakes recorded at seven permanent stations of Earthquake Research Center-Ferdowsi University of Mashhad-Iran. Two distinct parameters of shear wave splitting in terms of fast polarization orientation Ø and delay time δt are measured for each station using SKS and SKKS phases. Average time delays between fast and slow shear waves in Lut zone vary from 0.9 to 1.1s with fast polarization azimuth of 248° to 255° which will have a good coincidence with closing direction of Paleo-Tethys Ocean if 135º anti-clockwise rotation of Central Iranian Microplate has been removed. The closing direction of Ocean have reserved well at north of Darouneh fault with no rotation in terms of fast polarization axis, however most of stations in this region show null measurements that may be due to a large amount of vertical strain caused by the crust and subcontinental mantle deformation. The style of deformation in NE Iran changes from east to west by pure shear to simple shear, respectively. We clearly find that the azimuth of fast axis coherently changes to make parallel with major strike slip active faults –Shahrud fault system- in the former region.