Seismic Anisotropy of Upper Mantle Beneath the Ordos Block and Adjacent Regions

Abstract

Based on the polarization analysis of teleseismic SKS waveform data recorded at 90 broadband stations in the Ordos block and adjacent regions, the splitting parameters of fast polarization direction and delay time between the fast and slow shear waves are determined for each station using the minimum transverse energy method, yielding the images of upper mantle anisotropy. Combined with the GPS horizontal velocity field with respect to the Ordos block during 1999~2007, we analyze the seismic anisotropy as well as the crust‐mantle coupling beneath the Ordos block and its adjacent regions. At last, a new understanding of the block movement and the dynamic causes of the adjacent fault zones is achieved. The results reveal that there are nulls in the block which show an obvious isotropic characteristic. The delay time of the adjacent stations is obviously greater than those in the central block, which indicates an obvious anisotropy. The fast polarization directions are compatible with the tectonic strike direction and the horizontal velocity direction, which shows the crust‐mantle coupling. The differences between the directions at some stations may be associated with the early block activities. According to the SKS shear wave splitting results and the current GPS velocity field, we suggest that the Ordos block has no rotation. Meanwhile, the horizontal and ascending intrusion and the transverse extension of the plastic material in the upper mantle lead to the bifurcated flow around the Liupan Shan Mountains in the southwestern margin of Ordos. The generation and development of the Fenwei graben are the result from upward intrusion and lateral spreading of upper mantle material along deep faults.

Mantle Flow and Dynamics Beneath Central‐East China: New Insights From P‐Wave Anisotropic Tomography

“…Tian & Santosh, 2015), the asthenosphere (X. Y. Yang et al, 2019) or both (P. Wu, Wang, et al, 2012). In our study, the Vp azimuthal anisotropy is mainly attributed to the LPO due to the thermal flow or the stress.…”

“…Figure 14c shows that the FVDs of the P ‐wave and the S ‐wave are almost orthotropic. The previous studies suggested that the anisotropy estimated from shear‐wave splitting measurements may originate from the lithosphere (X. Tian & Santosh, 2015), the asthenosphere (X. Y. Yang et al., 2019) or both (P. Wu, Wang, et al., 2012). In our study, the Vp azimuthal anisotropy is mainly attributed to the LPO due to the thermal flow or the stress.…”

Asthenospheric Flow Channel From Northeastern Tibet Imaged by Seismic Tomography Between Ordos Block and Yangtze Craton

“…Therefore, there has to be YU ET AL. (Chang et al, 2011(Chang et al, , 2016Hu et al, 2011;Huang et al, 2008;León Soto et al, 2012;J. Li et al, 2011;Y.…”

“…(a) shows the average P-wave velocity perturbations from 150 to 250 km. Red bars represent fast-polarization directions and splitting delay times of previous SKS-splitting analyses(Chang et al, 2011(Chang et al, , 2016Hu et al, 2011;Huang et al, 2008;León Soto et al, 2012;J. Li et al, 2011;Y.…”

Study on effective elastic thickness of lithosphere and its tectonic significance in surrounding area of Ordos Block

“…These earthquakes are all distributed in the Ordos surrounding fault zone and faulted basin, but no earthquakes of Ms6.0 or above have ever occurred in the Ordos Basin. Previous studies have focused on crustal deformation, velocity structure, electrical mechanism, deep thermal structure and crustal stress field in the Ordos Block [3][4][5][6][7][8][9][10][11][12][13], these research results have laid a good theoretical foundation and provided sufficient reference for this study.…”