Three‐Dimensional Model of the Lithospheric Structure Under the Eastern Tibetan Plateau: Implications for the Active Tectonics and Seismic Hazards

Abstract

Details of lithospheric structures in three‐dimensions (3‐D) are key to understanding the dynamics of crustal deformation and earthquakes in active orogenic systems. In this study, we develop a 3‐D model of the eastern Tibetan Plateau using the Skua‐Gocad software based on the latest Rayleigh wave tomography. We perform a quantitative modeling workflow to map the details of the Moho discontinuities and the high‐velocity anomalies. Then, we integrate the topography, major active faults, large earthquakes, and crustal Poisson's ratios to analyze the relationship between the shallow and deep structures of this region. Our study shows that the Moho is generally coupled with the topography. A steep Moho ramp exists under the plateau margin and its surface projection intersects the Longmen Shan (LMS) at a low oblique angle (~22°). Active deformation and large earthquakes are related to the steep Moho ramp under the plateau margin. Moreover, based on a 3‐D model of the Poisson's ratio perturbations, we find that deformation across the central LMS is characterized as a crocodile‐type wedge in the crust and lithospheric mantle, due to the resistance of the Yangtze craton and isostatic rebound. We suggest that a tectonic wedging model that contains both the upper‐crust thrusting and lower‐crustal thickening contribute to the LMS orogeny. Three‐dimensional visualization of the lithospheric structure is well suited to reveal the different levels of deformation and their relationships. Quantitative modeling methods provide effective constraints on the active blocks in the eastern Tibetan Plateau.

Differential Erosion and Sedimentation Process at the Longmenshan Foreland Basin, Eastern Margin of the Tibetan Plateau: Evidence From Analog Experiments

“…The evolution of the Longmenshan fold-and-thrust belt is characterized by multi-stage thrusting and denudation, indicated by syn-sedimentations and low-temperature thermochronology (Li and Ji, 1993;Gou, 2001;Wang et al, 2012). In particular, the crustal thickness, fault geometry, and kinematics, and exhumation pattern all show along-strike variation in the Longmenshan at the eastern margin of the Tibetan Plateau (e.g., Hubbard et al, 2010;Sun et al, 2018;Lu et al, 2019;Tan et al, 2019). Which resulted in the kinematic and deformation more complicated than that of our experiments.…”

Supplemental Material: Surface-wave tomography of the Emeishan large igneous province (China): Magma storage system, hidden hotspot track, and its impact on the Capitanian mass extinction

“…In Figure 1(B), the map of the Emeishan Large Igneous Province is compiled from the following sources: eruption center (Xu et al, 2004), uplift center (He et al, 2003), flood basalts exposed on the surface (He et al, 2003(He et al, , 2007Xu et al, 2004;Zhou et al, 2005;Zhang et al, 2006;Anh et al, 2011;Liu et al, 2017;Xiang et al, 2018) and drilled in wells (Q. Jiang et al, 2018), basaltic lava and volcanic craters buried in the Sichuan Basin (Ma et al, 2019;Xia et al, 2020), basaltic dikes (Li et al, 2015;Shen et al, 2018), borders of inner (I),intermediate (II), and outer (III) zones (Chung and Jahn, 1995;, fault traces (Ren et al, 2013;Lu et al, 2019). Two photos of the dike-dominated magma storage system in the outer zone of ELIP are annotated and shown in Fig.…”

Quantitative Study of Crustal Structure Spatial Variation Based on Gravity Anomalies in the Eastern Tibetan Plateau: Implication for Earthquake Susceptibility Assessment

“…The Qinghai‐Tibet Plateau (QTP) is a young plateau that has undergone large‐scale and high uplift during the collision and convergence of the Indian and Eurasian plates since 65‐50 Ma (Molnar & Tapponnier, ; Harrison et al, ; Molnar et al, ; Tapponnier et al, ;). The QTP and its surrounding areas show strong three‐dimensional changes in terms of the crustal thickness, seismic wave velocity, resistivity, and topography (Bai et al, ; Chen & Molnar, ; Lu et al, ). The spatial changes in the crustal structure are also reflected in gravity anomaly data.…”