A STUDY OF AZIMUTHAL P RESIDUALS AND SHEAR-WAVE SPLITTING ACROSS THE KUNLUN RANGE (NORTHERN TIBETAN PLATEAU)

The Kunlun fault system is an east-west transcurrent fault bordering t he Tibetan plateau that has experienced left lateral motion since 3 Ma . A linear army of one-component and three-component seismological sta tions was deployed across the Kunlun range for 4 months. P travel-time residuals define three basic units along the profile: the North Kunlu n unit, the South Kunlun unit and the Bayan Har unit. P residuals are a function of azimuth: P residuals are fast in the southern stations f or southern azimuths and in the northern stations for northern azimuth s. Measurements of shear-wave splitting of the S, ScS and SKS phases h ave been performed on deep events. Delay times and fast polarization d irections have been computed by finding the maximum of the cross-coil- elation between the two horizontal components rotated at different ang les. Delay times from 0.40 s to 2.52 s remain in the range of those fo und by McNamara et al. (1994, J. Geophys. Res., 99: 13655-13665) at tw o sites along the same profile. P-Residual travel times and the splitt ing of S waves are discussed in relation to models of the geological e volution of this region. The Northern Tibetan plateau appears as a jux taposition of different terranes. The azimuthal P-residual pattern imp lies that P-wave anisotropy is about 3% in the lithosphere on both sid es of the Kunlun Fault and that fast velocities are oriented outwards from the Kunlun fault plane. S-Wave splitting is observed far from the fault and implies that the lithosphere beneath northern Tibet has und ergone an important deformation.