The Tangshan M(S)7. 8 earthquake in 1976 was located at the transitional part between the Yanshan fold and the North China Plain. The research on the existing crustal structure in the earthquake area is still not fine enough, and there are some controversies in the understanding of its seismogenic tectonic conditions. Combining the high-resolution Bouguer gravity anomaly data in Tangshan earthquake area with the latest global gravity field model WGM2012, based on wavelet multi-scale signal separation technology and spatial domain iterative inversion algorithm, the Moho surface fluctuation and the inner crust density disturbance distribution images in the earthquake area are obtained. The results show that the Tangshan earthquake area is located on the east side of Taiyuan-Yanqing Buge gravity anomaly gradient belt (that is, the middle part of the famous gravity gradient belt in eastern China) and the Moho steep belt, its isoline curves from NNE to NE, and the Moho depth is between 32 similar to 37 km. The epicenter of Tangshan is located in the transition between Moho steep belt and uplift area. The internal density distribution of the crust in the earthquake area presents the characteristics of high in the south and low in the north, and the scattered high-density bodies in the shallow part gradually aggregate with increasing depth. The former reflects the difference of tectonic movement between the North China Plain and Yanshan fold, while the latter reflects that the shallow high-density bodies mainly originate from deep upper mantle magmatism. From the density structure profile of the vertical and parallel Tangshan fault, it can be found that the Tangshan fault runs through the Moho surface, and its deep (about >7 km) pre-existing fracture surface is gradually opened by the intrusion of upper mantle magma under the action of horizontal tension and uplift compression of Moho surface, and the magma expands more and more as it goes up. The relatively uniform shallow part (within a depth of about 7 km) may be due to the continuous deposition of new strata and diagenesis on the surface, which prevents magma from invading, thus forming a locking area where stress and strain are easy to accumulate at the top of high-density body. This may be an important reason why the Tangshan earthquake occurred on the top of the high-density body and showed the characteristics of flower-like rupture in the shallow. Combining with the existing achievements, the seismogenic model of the Tangshan earthquake by the combined action of magmatic upwelling and faults is put forward from the point of view of material migration movement, and at the same time, it provides new evidence for the seismic sounding speculation of the seismogenic structural conditions of the Tangshan earthquake.

The Huangling Anticline, which formed during the Jinning movement, is the structural core of the Yangtze River Three Gorges area. In this study, we investigated the geological structure of the Huangling Anticline through correlation analysis among magnetic, Bouguer gravity, and crustal susceptibility anomalies of the Three Gorges and adjacent areas. Aeromagnetic anomalies, which were processed by reducing to the pole, reveal four main aeromagnetic anomaly regions. Three-dimensional (3D) magnetic susceptibility constrained inversion was used to obtain the susceptibility distribution from 0 to 30 km depth. We focused on the spatial distribution of four major rock masses: Sandouping, Huanglingmiao, Dalaoling, and Xiaofeng. The low susceptibility of the Huanglingmiao rock mass is tentatively explained by the combined effect of weathering and stripping of the upper body and a tectonic ductile shear zone at the bottom.

The complex geological structure of the Helan-Yinchuan Graben and adjacent areas is of great significance to study on shallow and deep structures of this area. In this paper, the gravity normalized total gradient method and 2-D wavelet multi-scale decomposition method are used to analyze the vertical and transverse structures in this region. The results show that the tendency and dip angle of the value of the high-low gradients match with the fault distributions, such as the eastern Helan mountain piedmont fault, Yinchuan fault and Yellow River fault. The intersection depth of the western Helan mountain piedmont fault and Helanshan-Donglu fault is about 18 km, and the intersection depth of Yinchuan fault and the Yellow River fault is about 25 km. The results of 2-D wavelet multi-scale decomposition show that the Zhengyiguan fault, western Helan mountain piedmont fault, Luhuatai fault and Yinchuan fault are confined to upper crust, while the eastern Helan mountain piedmont fault, Qingtongxia-Guyuan fault and the Yellow River fault extend down to lower crust. These three faults may be the southeastern boundaries of the Alxa block and the southwestern boundaries Ordos block, respectively. The epicenter of the Pingluo M8. 0 paleoearthquake intersected with Yinchuan fault at the depth of the gravity profile about 15 km, where the high-low gradient is a strong deformation zone. At the same time, the epicenter of the 1739 Pingluo M8. 0 earthquake is also located at the place of low gravity anomalies on the gradient belt. Therefore, it can be inferred that the seismogenic structure of this event is the Yinchuan fault. These conclusions can improve the understanding of the geological structure of the Helan-Yinchuan Graben and its adjacent areas, providing a scientific basis for the study of crustal dynamics and seismogenic mechanism of najor earthquakes.

为研究三河-平谷地震区浅层构造背景、地震孕育机理及地震与构造的关系，利用高精度重力异常数据，采用基于块体生长模式的重力三维反演算法对地震区浅层三维密度结构进行反演，并通过模拟试算验证基于块体生长模式反演方法的有效性和稳定性。高精度布格重力异常显示，三河-平谷8.0级地震位于大兴重力局部高、三河-马坊重力局部高与大厂重力低之间的交汇过渡低值区域。研究区浅层三维密度结构反演结果表明，1679年三河-平谷M8.0地震明显受NE向夏垫断裂控制，断裂两侧密度差异明显且向下延伸约10 km，推测发震部位深约10 km。

In this paper,we present an open python procedure with Jupyter notebook,for data extraction and vectorization of geophysical explo ration profile.Constrained by observation routes and traffic conditions,geophysical exploration profiles tend to bend curved roads for easy observation,however,it must be projected onto a straight line when data processing and analyzing.After projection,we don’t know the true position of the obtained crustal structure.Nonetheless,when the results used as an initial constraint condition for other geophysical inversion,such as gravity inversion,we need to know the true position of the data rather than the distance to the starting point.We solved this problem by profile vectorization and reprojection.The method can be used for extraction data of various geophysical exploration profiles,such as seismic reflection profiles,gravity profiles.