Crustal Azimuthal Anisotropy Beneath the Central North China Craton Revealed by Receiver Functions

Abstract

To characterize crustal anisotropy beneath the central North China Craton (CNCC), we apply a recently developed deconvolution approach to effectively remove near‐surface reverberations in the receiver functions recorded at 200 broadband seismic stations and subsequently determine the fast orientation and the magnitude of crustal azimuthal anisotropy by fitting the sinusoidal moveout of the P to S converted phases from the Moho and intracrustal discontinuities. The magnitude of crustal anisotropy is found to range from 0.06 s to 0.54 s, with an average of 0.25 ± 0.08 s. Fault‐parallel anisotropy in the seismically active Zhangjiakou‐Penglai Fault Zone is significant and could be related to fluid‐filled fractures. Historical strong earthquakes mainly occurred in the fault zone segments with significant crustal anisotropy, suggesting that the measured crustal anisotropy is closely related to the degree of crustal deformation. The observed spatial distribution of crustal anisotropy suggests that the northwestern terminus of the fault zone probably ends at about 114°E. Also observed is a sharp contrast in the fast orientations between the western and eastern Yanshan Uplifts separated by the North‐South Gravity Lineament. The NW‐SE trending anisotropy in the western Yanshan Uplift is attributable to “fossil” crustal anisotropy due to lithospheric extension of the CNCC, while extensional fluid‐saturated microcracks induced by regional compressive stress are responsible for the observed ENE‐WSW trending anisotropy in the eastern Yanshan Uplift. Comparison of crustal anisotropy measurements and previously determined upper mantle anisotropy implies that the degree of crust‐mantle coupling in the CNCC varies spatially.

Shear Wave Splitting Evidence for Keel‐Deflected Mantle Flow at the Northern Margin of the Ordos Block and Its Implications for the Ongoing Modification of Craton Lithosphere

“…Therefore, from splitting measurements alone, we are not able to quantitatively analyze the splitting pattern with respect to back azimuth and rule out the possibility of a multilayered anisotropy structure in the lithosphere and asthenosphere. Although the crustal contribution to the observed splitting delay time could be significant in some areas (e.g., Reiss et al, 2016), receiver function analyses imply that accumulated delay time due to crustal anisotropy is ~0.20 s beneath the WNCC and TNCO (Xu et al, 2018; Yang et al, 2018; Zheng et al, 2019). This is significantly smaller than the regional average, suggesting that the upper mantle is the primary source of the observed anisotropy.…”

Crustal Anisotropy Beneath the Trans-North China Orogen and its Adjacent Areas From Receiver Functions

“…The mechanism of crustal deformation is important in understanding the tectonic evolution and seismic hazards in this study area. However, the details on crustal deformation beneath the TNCO and its adjacent areas are still being discussed and debated recently (Tian and Zhao, 2013;Zhang et al, 2016;Yang et al, 2018;Schellart et al, 2019;Zheng et al, 2019;Cai et al, 2021;Chang et al, 2021). Further studies on crustal structure and anisotropy are essential for constraining the crustal deformation mechanism.…”

“…Based on these methods, crustal anisotropy beneath the southeastern and northeastern Tibetan plateau was calculated to investigate the mechanism of the crustal deformation and thickening (Sun et al, 2012;Wang et al, 2016;Xu et al, 2018). Yang et al (2018) and Zheng et al (2019) also measured the splitting of the Moho Ps phases from receiver functions and observed the spatial distribution of crustal anisotropy beneath the northeastern TNCO, respectively. Results mentioned above confirmed that crustal anisotropy has been successfully estimated from the splitting of the Moho Ps phases and performed to study the crustal deformation.…”

Deformation of the Crust and Upper Mantle beneath the North China Craton and Its Adjacent Areas Constrained by Rayleigh Wave Phase Velocity and Azimuthal Anisotropy

“…Recently, many studies revealed the velocity structure and seismic anisotropy beneath the crust and upper mantle of the NCC [23,[25][26][27]. However, these results on understanding the lithospheric thinning and deformation of the NCC are still controversial.…”

“…Seismic anisotropy is often used to investigate the deformation of the crust and upper mantle. The S-wave splitting studies provide useful information about anisotropy in the crust and upper mantle [24,26]. However, the depth of the anisotropic structure is usually difficult to obtain by S-wave splitting.…”