On 4 February 1975, the Haicheng Ms 7.3 earthquake occurred in the Liaodong Uplift, northeastern China. To investigate its seismogenic structure and deep geological environment, we acquired broadband magnetotelluric data along two intersecting profiles across the epicentral region and performed three-dimensional inversion. Two orthogonal electrical sections were then extracted from the resulting 3D resistivity model to image the crustal structure beneath the Haicheng earthquake area. The model reveals that the northern segment of the Tanlu fault corresponds to a major electrical discontinuity between the Xialiaohe Basin and the Liaodong Uplift, suggesting that it may represent a deep-seated fault zone extending into the lithosphere. Beneath the Liaodong Uplift, a prominent mid-crustal low-resistivity layer is developed, and a synform conductive body is resolved beneath the source region. The Haicheng mainshock and relocated aftershocks are mainly distributed along the interface between this conductive body and the overlying high-resistivity upper crust. In addition, the Haichenghe–Dayanghe fault is imaged as a conductive zone that connects the mid-crustal conductor with shallower crustal levels. These electrical features suggest that deep crustal fluids, possibly related to Pacific Plate subduction and craton destruction, may have migrated upward along fault zones, weakened the seismogenic fault system, and promoted earthquake nucleation. Compared with the volcanic regions of the Jilin–Heilongjiang orogenic belt, where conductive anomalies extend into the upper mantle, the Haicheng region is characterized mainly by intracrustal conductors. This contrast highlights the role of crustal-scale conductive structures in the seismogenic environment of the Haicheng earthquake and provides geophysical constraints for comparing earthquake- and volcano-related deep processes in northeastern China.

The Yilan-Yitong Fault Zone, a core part of the northern Tanlu Fault Zone, is a key seismogenic structure in Northeast Asia. Its Liaoning segment suffers from unclear surface distribution, insufficient late Quaternary activity evidence and lack of refined research based on optimized multi-source remote sensing data, which restricts regional seismic hazard assessment and major engineering safety layout. This study aimed to conduct fine detection and activity evaluation of this fault segment using high-resolution satellite data. We took GF-2 panchromatic and Sentinel-2 multispectral images as core data, compared four fusion algorithms (PCA, GS, HSV, Brovey) via qualitative and quantitative evaluation, and combined UAV remote sensing, field surveys of 28 key observation points and large-scale trench (25 m × 8 m) verification in Kaiyuan for systematic analysis. Results showed the PCA algorithm had the optimal comprehensive performance, suitable for fine geological interpretation. The fault was divided into three subsegments, with the Tieling-Kaiyuan segment showing distinct linear geomorphology and strong late Quaternary activity. The trench provides evidence suggestive of Holocene activity, and flower structures plus multi-phase faulting events reflected multistage activity characteristics, with preliminary identification of paleoseismic relics. This study verifies the application potential of domestic high-resolution satellites, fills the gap in refined activity research of the fault’s Liaoning segment, and provides high-precision scientific support for Liaoning’s seismic hazard assessment and major engineering safety layout.