Crustal Structure Beneath the Southeastern Tibetan Plateau and Yunnan Province Using Teleseismic Data

To explain the development of the India-Eurasian continent-continent collision, it is necessary to constrain the characteristics of the lithosphere of the Tibetan Plateau and surrounding regions. The crustal structure beneath the SE Tibetan Plateau and adjacent off-Plateau Yunnan Province was illuminated using the receiver function method. The Moho depth in Tibet was found to be ~70 km, decreasing off-Plateau to ~60 km in northern Yunnan, and further decreasing to ~40 km in southern Yunnan. The gradual change in crustal thickness matches the gradual topography change over this region. The lower crustal flow model (Clark and Royden, 2000) predicts anisotropy and a low velocity (weak) zone in both Tibet and Yunnan Province. The Flesch et al. (2005) model predicts anisotropy and shear between a decoupled crust and mantle only in Yunnan. Crustal anisotropy manifests as backazimuth variability on the radial and transverse components (Sherrington et al., 2004). A positive velocity discontinuity at ~40 km depth in northern Yunnan is observed on the radial component with backazimuth variability (strongest at backazimuths of 100 degrees to 150 degrees). However, no backazimuth variability was observed on the transverse component in either Tibet or Yunnan. We see a positive velocity discontinuity in Yunnan at ~20km depth and in SE Tibet at ~43km, but we observe no negative velocity discontinuities or low velocity zones. We see no evidence of anisotropy or crustal flow in Tibet, and possible evidence of anisotropy in Yunnan. These results agree with the Flesch et al., 2005 model in Tibet, disagree with the lower crustal flow model in Tibet, and are inconclusive in Yunnan Province.