The Central Asian Orogenic Belt (CAOB) is a globally magnificent accretionary orogenic belt that has been formed since the Phanerozoic as a result of the Paleozoic closing of the Paleo-Asian Ocean (PAO). The transition zone between the North China Craton (NCC) and the Siberia Plate is located in the eastern CAOB and has been thoroughly investigated by various seismic investigations. However, other types of geophysical approaches lag behind, especially integrated magnetic-gravity surveying, which could provide regional continent-scale constraints on the deep crustal structure. Here, the high-resolution ground gravity and airborne magnetic data covering the study region are newly processed by upward continuation, an improved potential field normalization differential algorithm, an analytical signal approach, and correlation analysis. The processed gravity and magnetic anomalies reveal dominant differences between the CAOB and the northern margin of the NCC; these regions are tectonically divided by the upper crustal Chifeng-Baiyan Obo fault, which is expressed by an important geological boundary. In the middle and lower crust, this tectonic boundary extends northward to the Xar Moron fault. Unexposed Mesozoic granites may be distributed extensively in the mid-lower crust along the Solonker suture zone. The local negative correlation characteristics of gravity and magnetic anomalies may be related to the structural fabrics derived from the convergence of the two terrains.

Utilizing short-period dense seismic arrays, ambient noise tomography has proven effective in delineating continuous geological structures, a task critical for characterizing shale gas reservoir configurations. This study deployed 153 short-period seismic stations across the Xiahuayuan District in Zhangjiakou, a region with prospective shale gas deposits, to perform an ambient noise tomography survey. Through a meticulous process involving cross-correlation analysis, dispersion curve extraction, and subsequent inversion, a three-dimensional velocity structure model of the area was constructed. The model discerns subtle velocity changes within the 0–3 km depth interval, achieving a horizontal resolution of approximately 1.5 km in the 0–3 km stratum, thereby effectively delineating the shale reservoir structure. Integration of the velocity model with regional geological data facilitated a comprehensive interpretation and structural analysis of the prospective shale gas zone. Low-velocity anomalies observed within the velocity structure correspond to the spatial distribution of the Xiahuayuan Formation, likely attributable to the prevalent stratum of mudstone shale deposits within this formation. Employing a binary stratigraphic model, the study predicted shale content based on the velocity structure, with predictions exhibiting a moderate correlation (correlation coefficient of 0.58) with empirical data. This suggests the presented method as a viable rapid estimation technique for assessing the shale content of target strata.