High-Resolution Seismic Velocity and Attenuation Models of Eastern Tibet and Adjacent Regions (Post Print)

Abstract : High-resolution seismic velocity and attenuation models of the Tibetan Plateau and adjacent regions of western China are critical to monitoring seismology efforts in Eurasia. Our waveform data are collected from new deployed seismic networks including NETS (North-Eastern Tibet Seismic experiment), INDEPTH-IV-ASCENT, INDEPTH-IV-UK, and previous networks, comprising an unprecedented coverage of the eastern half of the Tibetan plateau. Three seismic methods are used in the velocity structure in this region: Pn velocity tomography, body-wave finite-frequency tomography, and Rayleigh wave phase velocity. We observe consistent anomalies in the crust and upper mantle using all of these methods. These anomalies include a low velocity in northern Qiangtang and the Songpan-Ganzi fold belt and the high velocity in the Qaidam Basin. QLg and QPg models have been determined using a Reverse Two-station/event Method, which shows a high seismic attenuation zone along the Kunlun belt. We have also observed significant azimuthal anisotropy of seismic Q. The isotropic seismic Q, suggested as an estimate of QS for the crust, is low in northern Qiangtang and the Songpan-Ganzi. The high-Q directions parallel major fault planes in eastern Tibet, and correlate with fast-direction of shear wave splitting and Rayleigh wave azimuthal anisotropy fast directions, which suggests a coherency of deformation between the crust and upper mantle in this region. Similarly, a high velocity and high Q block in southeastern Tibet around eastern Bangong-Nujiang Suture and Eastern Himalaya Syntaxis correlates well with the high velocity in this region.