Seismic Structure of the Crust and Upper Mantle Beneath SE Tibet Revealed by Ambient Noise Full-Waveform Inversion

The southeastern margin of the Tibetan Plateau has experienced complex tectonic deformation since the Cenozoic collision between the Indian and Eurasian plates. In this study, Empirical Greens’ Functions (EGF) are extracted from the dense ChinArray (phase I) with over 350 broadband stations covering Yunnan and southern part of Sichuan, China. High-quality surface waves are selected from the EGFs and used for the Multi-Scale Time-Frequency Full Waveform Inversion (FWI) to construct a high-resolution crustal and uppermost mantle S-wave velocity model. Our results reveal a high-velocity anomaly extending from the upper crust down to ~100 km depth beneath the inner zone of the Emeishan Large Igneous Province, interpreted as a fossilized magma plumbing system within the lower crust and lithosphere. Additionally, two long low-velocity zones are bounded by major strike-slip faults, with large earthquakes predominantly occurring along these boundaries. The Xiaojiang Fault is first identified as a well-constrained low-velocity zone, cutting through the whole crust, separating the Yangtze and Sichuan-Yunnan high-velocity blocks, while the Red River Fault delineates the boundary between the Yangtze and Indo-China blocks at the lithospheric scale. The eastern boundary of the clockwise crustal material movement beneath the Southeastern Tibetan plateau might be further confined by the Xiaojiang Fault. The strong rotation movement along the Xiaojiang Fault potentially causes the shear heating or partial melting in the crust along the fault, consistent with the distribution of active crust-origin hot springs and high strain rate from GPS observations. In summary, this model shows higher resolution than the previous studies and provides new insights into the crust-lithosphere geodynamic processes and deformation patterns.