Investigation of Crustal Structure of the Ordos Block and Its Adjacent Regions along an N-S Profile at 107.6°E

The Ordos Block and its surrounding area has been a region of intense study for its important role in revealing the formation, evolution and destruction of North China Craton. Our study, in order to obtain crustal structure with higher resolution beneath the Ordos region, employed seismic data along an N-S profile at 107.6°E consisting of 27 temporary broadband stations from the newly deployed ChinArray-Himalaya II, stretching across Yinshan Oregon, Hetao Graben and Ordos Block. Also data of 17 stations from SOSArray and permenant CEA stations (Guo and Chen, 2017) at the south of this profile, crossing Weihe Graben and Qinling belt region, were added to enhance our further analysis. Receiver functions were first calculated for these stations with an iterative deconvolution in the time domain (Ammon, 1999). And a Kirchhoff migration method was employed to get a preliminary image of the Moho under this profile. Detailed structures in the crust and the Moho variation were then obtained with a joint inversion of our receiver functions and surface wave dispersion curves calculated by Li et al. (2018) beneath each station. Our reference shear velocity model for the migration and joint inversion was from Li et al. (2018) and corrected concerning the thick sediments (Wang et al., 2017) at some sites. The results reveal that Moho is generally flat at about 43 km depth in the northern part of Ordos, and goes deeper to about 49 km in the southern part. To the north of Ordos, under the Hetao Graben, Moho is also deeper with a depth of 45-48 km. To the south of Ordos, crust is thinned to about 41 km beneath Weihe Graben and then thickened under the Qinling belt with a deepest Moho at about 53 km. In addition, the migration image and joint-inverted velocities under the Ordos Block display differences bounded by 38°N, which may indicate different tectonic histories of the two parts.