Distinct lateral variations of upper mantle anisotropy beneath eastern China revealed by shear‐wave splitting

Abstract

[1] A dense seismic array consisting of 28 temporary stations was deployed to study the crustal and upper-mantle deformations beneath eastern China. We measured the splitting parameters in the crust and mantle by analyzing P-to-S phases converted at the Moho discontinuity (called PmS phases) and the core-mantle boundary (i.e., core phases), respectively. The splitting parameters of core phases are retrieved at most stations while that of the PmS phases are retrieved at only a few stations. Distinct lateral variations of the fast polarization directions analyzed with the core phases are found in different tectonic blocks in eastern China. The delay times in the mantle and crust are moderately large (~1 s) and averagely smaller than 0.3 s, respectively. By the Fresnel-zone analysis, the laterally variant lithospheric anisotropy is revealed between the two sub-blocks (Southeast China Orogenic Belt and Yangtze Craton) of the eastern South China Block. In contrast, in the southeastern North China Craton, the anisotropy in a relatively deep layer contributes to the splitting observations.

Crustal Structure and Anisotropy in the Lower Yangtze Region and its Metallogenic Implications

“…The LYB has a total of 20 stations and the rose diagram shows a consistent NE-SW fast wave direction for all the stations except for C032, C035, and the two stations close to the Tanlu Fault (F4). Our results are consistent with results revealed by shear wave splitting analyses (Huang et al, 2013). The average polarization direction was 45 °and delay time was 0.35 s, which is larger than that for the NCB.…”

“…There are a total of 10 stations in the NCB, and the delay time was approximately 0.2 s, indicating weak crustal anisotropy (Shahzad et al, 2021;Wu et al, 2021). The fast directions of the stations close to the Xinyang-Shucheng Fault (F5) were approximately NW-SE, which is nearly parallel to the fault direction and consistent with previous results (Huang et al, 2013;Shi et al, 2013). The LYB has a total of 20 stations and the rose diagram shows a consistent NE-SW fast wave direction for all the stations except for C032, C035, and the two stations close to the Tanlu Fault (F4).…”

Azimuthally Anisotropic Structure in the Crust and Uppermost Mantle in Central East China and Its Significance to Regional Deformation Around the Tan‐Lu Fault Zone

“…(2018) employed seismic anisotropy from shear‐wave splitting and receiver functions. Their results showed moderately large and averagely small delay times for mantle and crust, respectively (H. Huang et al., 2013; Y. Yang et al., 2018). However, the quantitative estimates and the depths of occurrences of the inferred components of seismic anisotropy were not estimated.…”

P wave radial anisotropy tomography of the upper mantle beneath the North China Craton

“…A combination of frozen‐in lithospheric anisotropy from the past deformation processes, shear coupling between the lithosphere and asthenosphere, and current mantle flow in the asthenosphere is suggested to be the main contribution to seismic anisotropy under continents [ Park and Levin , ; Yuan et al ., ]. Our knowledge of the anisotropic structure beneath the NCC comes mostly from studies of shear wave (SKS) splitting measurements [e.g., Huang et al ., ; Zhao et al ., ; Zhao and Xue , ]. The azimuthal anisotropy deduced by shear wave splitting measurements has provided much geodynamic information beneath the NCC, but it has poor depth resolution and the estimated anisotropic strength is influenced by the thickness of the assumed anisotropic domain.…”