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The deformation mechanism in southeastern Tibet since the continental collision between the Indian and Eurasian plates could be explained by several models, including two major classic end-member models, the rigid-block extrusion model and the crustal flow model. Crustal channel flow is likely an important tectonic regime for properly explaining a large number of geological and geophysical observations but remains in competition with the block extrusion model. Consequently, detecting ductile flow connectivity would play a key role in understanding the tectonic evolution of the southeastern Tibetan Plateau. Here, we established a high-resolution broad-band Q Pg model for the crust in SE Tibet by using a joint inversion tomography method based on both single- and two-station Pg data. We verified the stability of the Q Pg tomography by comparing the Q Pg values at 1 Hz between the joint inversion and the two-station method. Two low- Q Pg zones were observed, isolated by the high- Q Pg Emeishan large igneous province (ELIP). Strong Pg attenuation beneath the Songpan-Ganzi Block and Western Sichuan Block may indicate the presence of crustal material flow due to relatively weak rheological strength. Cooled basaltic magma remnants in the inner zone of the ELIP likely block the southeastward migration of crustal materials driven by the gravity and lateral pressure gradient, and restrict the flow to the Western Sichuan Block, resulting in surface uplift and crustal thickening. Strong Pg attenuation near the Xiaojiang Fault and the Red River Fault may result from mantle upwelling in this region. Our Q Pg model, combined with previous results, suggests that the tectonic deformation in the southeastern Tibetan Plateau has been mainly controlled by the effects of crustal channel flow and asthenospheric upwelling since the Late Miocene. [ABSTRACT FROM AUTHOR]

The continuous convergence between the Indian and Eurasian plates caused massive lithospheric deformation in the Tibetan Plateau and led to excessive crustal material escaping through its southeastern margin. However, the mechanisms that accommodate the escaping materials and whether they intrude into the Indochina Peninsula are continually under debate. Seismic Lg waves mostly propagate within the crust waveguide with an amplitude decay that is sensitive to crustal material properties, such as temperature, partial melting, and fracture. Therefore, Lg attenuation can be a useful indicator of potential crustal material escape. In this study, we developed a high‐resolution broadband Lg attenuation model in this region between 0.05 and 10.0 Hz, with the resolution reaching 1° in regions with dense raypath coverage. Prominent low‐Q anomalies beneath the southeastern margin of the Tibetan Plateau, correlating with previously observed low velocity, high conductivity and high Poisson's ratio, may indicate possible high temperature and/or partial melting within a relatively weak crust, and suggest a north‐south interconnected corridor for gravity‐driven material flow. Through our results and other geological and geophysical observations, a dynamic model is suggested here by combining shallow rigid block extrusion and deep viscous crustal flow to explain crustal material escape in the southeastern margin of the Tibetan Plateau. Additionally, neither shallow extrusion nor deep material flow enter the Indochina Peninsula based on the relatively high Q values, which indicate a stronger crust there. Key Points: A high‐resolution broadband Lg attenuation model in southeast Tibetan crustWeak crust in the southeastern Tibetan Plateau revealed by strong Lg attenuationThe Tibetan crustal flow for material escape does not stretch into the Indochina Peninsula [ABSTRACT FROM AUTHOR]

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 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. [Copyright &y& Elsevier]