The Poisson Ratio and Crustal Structure of the Central Tibetan Plateau Inferred from Indepth‐III Teleseismic Waveforms: Geological and Geophysical Implications

Abstract

AbstractTeleseismic conversion and multiple waves recorded by the INDEPTH III seismic array have been used to investigate the crustal thickness and VP/VS ratios of the central Tibetan Plateau. The comparison with crustal thicknesses obtained from other studies shows good agreement, which suggests that our measurements are reliable. Our results reveal that the crustal thickness is 65±5km beneath central Tibet. On the average, the Moho beneath Qiangtang is 5~6km shallower than that below the Lhasa terrane. A ~10km Moho offset occurs along the BNS, which maybe the result of northward subduction of the Lhasa mantle lid beneath the Qiangtang terrane affected by the India‐Asia collision. Due to extensive crustal melting/fluid beneath the central Tibet, the average crust Poission's ratios are high (0.25~0.32). The high Poission's ratio abnormality in the northern Lhasa may be related to the Bong Co‐Lhari fault. Another high Poission's ratio abnormality located on the northern Qiangtang terrane (st36~st40) can be related to the crustal partial melting arising from the high heat flux from abnormal upper‐mantle beneath the north‐central plateau.