Crustal flow pattern beneath the Tibetan Plateau constrained by regional Lg-wave Q tomography

Abstract

As a prominent geophysical anomaly, unusually high seismic wave attenuation is observed in the crust and upper mantle of the Tibetan Plateau, particularly along its northern area. Theoretical and laboratory investigations show that the strong seismic attenuation can indicate high temperatures and partial melting, which may decrease the viscosity of the material and cause it to flow. Thus, seismic attenuation distribution may provide useful constraints to the crust flows if they exist. Using Lg-wave Q tomography, we construct a 0.05–10.0 Hz broadband high-resolution crust attenuation model for the Tibetan Plateau and its surrounding regions. The maximum spatial resolution is approximately 1.0°×1.0° in well-covered areas and for frequencies between 0.05 and 1.5 Hz. This attenuation model reveals an apparent low-QLg belt stretching along the northern and eastern Tibetan plateau. Combining the Lg-wave Q model with other geophysical data, two possible crust flow channels are found in the Tibetan Plateau. The main flow channel is from north to east and then turns to southeastern Tibet along the western edge of the rigid Sichuan basin, while a second channel starts from southern Tibet and crosses the Eastern Himalayan syntaxis.