• 标题：Three dimensional P-wave velocity structure underneath the southeastern margin of the Tibetan Plateau and the deep tectonic significance
• 关键词：P-wave velocity structure ,Tibetan Plateau, deep tectonic significance
• 作者：Dahu Li, Zhifeng Ding, Yan Zhan, Lijun Chang

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The deep velocity structure underneath the southeastern margin of the Tibetan Plateau is the key to understand the tectonic evolution of the Tibetan Plateau. In this study, 145254 relative travel-time residuals were measured from the records of 1360 teleseismic events using the waveform correlation method, we determined the three-dimensional (3-D) P-wave velocity structures in the upper mantle using a large-scale dense seismic array. The western boundary of the Yangtze Craton extends from the Longmenshan fault zone in the north to the Red-River fault in the south, our imaging results show that in a depth range of 50–150 km, obvious differences in physical properties of the medium exist across the Longmenshan fault zone. The Red-River fault and the Xiaojiang fault are the western and eastern boundaries of Chuan-Dian diamond block, respectively. Low-velocity anomalies are visible from the north of the Red-River fault to the east of the Xiaojiang fault and their intersection region. The high-velocity anomaly below the Sichuan Basin is thinning westward, with the thickness of 350 km below eastern Sichuan Basin. We obtained a low-velocity anomaly extending 400 km below the Tengchong volcanic field. A high-velocity anomaly, extending down to the mantle transition zone, is thought to be related to the subduction of the Indian slab. Our results also reveal an obvious low-velocity anomaly exists to the south of 26°N, we speculate that the flow of the upper mantle material beneath the Tibetan Plateau affects the velocity structure in this region.