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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 crustal attenuation structure can effectively reveal the rheology and thermal properties of different geological blocks, and can provide seismological constraints on regional tectonic evolution. Based on 11 306 vertical-component Lg-wave seismograms recorded at 111 broad-band stations from 891 crustal earthquakes that occurred between 1994 and 2020, a broad-band Lg-wave attenuation model is obtained for Southeast Asia. This study demonstrates the capability of applying crustal Lg-wave attenuation inversion in a complex region mixed with continents, islands and marginal seas. The resolution approaches 2° in most parts in the study region. Lg blockages are observed at places with sharp Moho depth changes. The resultant Q models are consistent with regional geologic structures provided by previous studies. Prominent low-attenuation anomalies are located in the Sundaland Core containing stable ancient crust, including Indochina, Malay Peninsula, East Sumatra, Sunda Shelf and Borneo Core. Regions with strong attenuation are associated with complex tectonic conditions, such as the Indo–Australian subduction zone, sutures in Sarawak and Sabah. The observed Lg-wave attenuation characteristics provide constraints on the tectonic affinities and evolutions of the geological blocks. The results show that the Borneo Core remained stable since its accretion with the Sundaland Core. Ancient blocks are characterized by weak Lg attenuation, whereas geologically younger terranes are often characterized by strong Lg attenuation, which can be exploited to better understand the separation and convergence of plates during the tectonic evolution. [ABSTRACT FROM AUTHOR]

The Lg-wave spectra are investigated for the 2019 Changning M L 6.0 earthquake and its 94 aftershocks with magnitudes above M L 2.8, which occurred in the southern Sichuan Basin, Southwest China. This earthquake sequence is potentially related to the water injection from nearby salt mining activities. Based on an established regional high-resolution broadband Lg-wave attenuation model, we correct the observed spectra for the attenuation effect along the propagation path. By fitting the observed spectra from the Changning earthquake sequence with the theoretical source model, we estimate seismic moments and corner frequencies, from which the stress drops are calculated for the entire earthquake sequence. The results show that the stress drops are rather scattered, ranging from 0.16 MPa to 32 MPa with a median value of 0.78 MPa. Spatiotemporal variation of stress drops reflects strong fault heterogeneity and a complex stress release process, which is likely influenced by water injection and diffusion. Positive trends are observed between the stress drop and focal depth and between the stress drop and seismic magnitude. Relatively lower stress drops for most shallow events are possibly the indication of lowered normal stress by long-term fluid injection. No apparent relation is observed between the stress drop and the distance to the Shuanghe salt mine, where water was injected. Combining the actual water injection data and previous numerical simulation studies, we suggest that the salt mining-related water injection may lead to elevated pore pressure beyond the source region of the 2019 Changning earthquake. The increasingly cumulated underground water may have created pathways linking multiple fault systems, thus the possibility of future large induced-earthquakes cannot be ruled out. • The Lg-wave source spectra are revised for the 2019 Changning earthquake sequence. • Stress drops are obtained by fitting source spectra based on the Brune's source model. • The lowered normal stress by long-term injection may lower the stress drops of most shallow events. [ABSTRACT FROM AUTHOR]