Shear wave tomography of China using joint inversion of body and surface wave constraints

Abstract

The India‐Eurasia collision and the decratonization of the North China Craton have drawn much attention from the scientific community. Here we provide the first large‐scale S wave velocity model for China (CH11‐S) based on constraints from both teleseismic surface and body waves. We take advantage of the recent deployment of the 140 permanent stations of the Chinese Digital Seismic Network and temporary network deployments to resolve both the lithospheric and deeper mantle structure. Slow velocities are widespread in the crust and upper mantle. Deeply rooted fast anomalies are located beneath the stable Yangtze Craton and the western (Ordos) block of the North China Craton. An upper mantle fast anomaly is observed beneath the eastern block of the North China Craton and could represent thermally eroded or delaminated Precambrian lithosphere. Another flat and fast feature appears beneath the Tibetan Plateau from 50 to 250 km depth. This may represent the Indian slab stalled in the mantle due to its buoyancy or a lithospheric instability triggered by the India‐Eurasia collision. A large fast anomaly apparently stagnant in the transition zone is observed beneath the Yangtze Craton and may play a role in the stability of this block. In contrast, on both sides of the South China Block, active and reactivated areas coincide with oceanic slab material that has already sunk into the lower mantle and that may have enhanced tectonic activity by forcing convection. Finally, the upper mantle beneath Tibet seems almost completely surrounded by adjacent high‐velocity and presumably strong blocks.

Distinct upper mantle deformation of cratons in response to subduction: Constraints from SKS wave splitting measurements in eastern China

“…This kind of division is in good agreement with previous studies of subsurface structures that used other methodologies (e.g., Obrebski et al, 2012). For the areas having substantially thicker lithospheric roots (>200 km), such as the Ordos and the Yangtze cratons (grey outlines in Fig.…”

“…Tomography models show that the lithosphere in this area is relatively thin, with an average thickness of b 100 km (Obrebski et al, 2012;Zhao et al, in press). These lines of evidence suggest that velocity anomalies reflect features in the asthenosphere.…”

Shear wave structure in the northeastern Tibetan Plateau from Rayleigh wave tomography

“…Our model shows relative low velocity anomalies along and to the south of the Kunlun and high velocity anomalies in northeast (Figure ). To the first order, this observation is consistent with large‐scale tomography models in Tibet [ McNamara et al ., ; Liang and Song , ; Pei et al ., ; Huang and Zhao , ; Yang et al ., , Li and van der Hilst , ; Obrebski et al ., ] that generally imaged low velocity anomalies beneath the Songpan‐Ganzi Terrane with the Kunlun fault as the northern boundary, indicating a hot and deformable lithosphere.…”

“…The most interesting feature in the 3‐D model of NE Tibet is a local low velocity anomaly in the shallow upper mantle beneath the restraining bend of the Kunlun fault (Figures and c), where high topography and thick crust are observed (Figures , , and ). Is this anomaly a local feature or a simple extension of the anomaly beneath the Songpan‐Ganzi Terrane as imaged in large‐scale models [ Yang et al ., , Li and van der Hilst , ; Obrebski et al ., ]? We conducted additional resolution tests to address this question.…”

Lateral Variations of the Mantle Transition Zone Structure beneath Eastern China

“…1a; e.g., Charvet et al, 1996). Seismic tomography studies revealed near horizontal high-velocity anomalies within the mantle transition zone (MTZ) beneath eastern China and interpreted them as the stagnant ancient slabs (e.g., Huang and Zhao, 2006;Zhao et al, 2007;Li and van der Hilst, 2010;Zhao et al, 2011;Obrebski et al, 2012;Wei et al, 2012). Therefore, the current thermal state around the MTZ may be influenced at the locations in which the slab still interacts with the MTZ.…”