Research on the three-dimensional electrical structure of the shallow portion of the southern segment of the Red River Fault (Dazhai Village)

No earthquake of magnitude six or greater has been recorded historically in the southern segment of the Red River Fault (RRF). This absence constitutes a significant seismic gap, suggesting a risk of future strong earthquakes. The China Earthquake Science Experimental Site intends to conduct drilling exploration in this area, which necessitates improved knowledge of the fault zone’s geometric distribution characteristics and deep structure. We obtained and analyzed audio and broadband magnetotelluric (MT) data collected at one of the alternative drilling stations (in the Dazhai Village of Honghe County). We have used these data to obtain a high-resolution 3-D electrical model of this study area’s subsurface to a depth of 5 km. We report that the electrical structure from the surface to 0.5 km is relatively complex, characterized by alternating high and low resistivity; below 0.5 km, the electrical structure becomes more simplified. The RRF extends northwest−southeast orientation along the high and low resistivity boundary, dipping northeastward. The electrical structure of the Red River Valley, which the fault zone traverses, reveals low resistivity characteristics with a lateral width of up to 2 km. This study offers critical electromagnetic constraints that enhance our understanding of the tectonic characteristics of the RRF. The findings will inform and aid in the design of drilling plans for the southern segment of the RRF region.