Azimuthal anisotropy of Lg attenuation in eastern Tibetan Plateau

Abstract

The Q of seismic phase Lg is measured to approach the crustal Qβ, which can be used to infer crustal rheology. A reverse two‐station/event method is used to measure the interstationQLg, which theoretically eliminates effects from the source and site response. Strong azimuthal anisotropy of 1/QLg in northern Tibet is observed, which approximately correlates with the seismic velocity anisotropy observed using both surface waves and teleseismic S waves. Both the intrinsic and scattering attenuation contribute the isotropic Q, whereas the anisotropic Q may be associated with the fractures and faults in the crust. Strong 1/QLgis observed in the northwestern Songpan‐Ganzi fold belt, where the high‐Qdirections correspond with the orientations of major strike‐slip faults. Intrinsic and scatteringQ values are estimated for different tectonic terranes in eastern Tibetan Plateau. The intrinsic Qvalues are approximately 500 in the northern Tibetan Plateau, which suggests a hot (∼700°C) crust, consistent with low seismic velocity measurements. Our result suggests that the crust of northwestern Songpan‐Ganzi fold belt may be hotter than that of the Qiangtang terrane, which may be related to the strain heating along the major strike slip fault zones that dominate the northernmost Tibet.