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As the west rim of an ejective fold zone, the Huaying Mountain fault zone (HMFZ) in the eastern Sichuan Basin (SB) plays an important role in the tectonic evolution of the SB. The distribution and characteristics of HMFZ are strongly associated with tectonic activities and have greatly impacted the distribution of oil and gas reservoirs. However, its distribution and characteristics have remained poorly understood due to a lack of geophysical data, especially areal gravity survey and magnetotellurics (MT) survey, which are admittedly advantageous for detecting the edges of geological structures. Therefore, we carried out the ground geophysical surveys that areal gravity survey and MT survey, and acquired 1:250,000-scale real gravity data and MT data for the first time in this area. Optimized edge-detection methods were adopted to process the areal gravity data, allowing us to characterize the planar distribution of faults more reliably and convincingly. We found that the southern HMFZ is well developed and primarily trends in NNE and NE, whereas the subordinate faults trend in N-S and W-E. Vertical information for the faults extracted using the improved depth from the extreme points method revealed that the fault dominantly dipped to the SE, which was consistent with the results of MT inversion. Based on the spatial distribution of the faults, we further discussed the gravity anomaly, fault distribution, Luzhou palaeo uplift, and the distribution and characteristics of oil-gas resources, and found the convincing evidence to analysis the distribution of oil and gas resources in this region.

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The spatial position and dip feature of the density boundary are significant to the study of fault and tectonic frameworks. Edge detection methods generally attach importance to the horizontal position of the boundary, but it is difficult to determine the dip feature expressly. A density gradient inversion method was proposed based on the corresponding relationship among the gravity forward field, forward kernel matrix, and model attributes. The inversion result of this method is that the density gradient value is different from the conventional gravity inversion. It can directly display the 3D distribution features integrated with 3D inversion results of the density gradient in different directions. The theoretical model means that the inversion results can not only identify the horizontal position of the boundary but also qualitatively determine the dip feature of faults. It has been widely applied to fault identification in the Songliao Basin. According to the joint inversion results, the strike feature and the dip feature can be quantitatively and qualitatively identified, respectively, making up for the shortcomings of sparse distribution and poor lateral resolution of existing seismic data.