Time-Lapse Three-Dimensional TEM Imaging and Damage Evolution of Hydraulic Fracturing in Landslide Fracture Zones

Landslide fracture zones play a critical role in slope instability, yet their hydraulic fracturing processes remain difficult to monitor using conventional geophysical methods. This study proposes a time-lapse three-dimensional transient electromagnetic (TEM) imaging approach to characterize fracture damage evolution in the Xiaolongdong landslide, Zhaotong City, China. Repeated TEM observations, integrated with GNSS displacement monitoring and environmental measurements, were used to reconstruct dynamic resistivity fields through three-dimensional inversion. Distinct resistivity precursor anomalies were characterized by a 3–8% increase followed by a rapid decrease. During hydraulic fracturing, resistivity decreased from 30 to 50 Ω·m to 8–15 Ω·m, reflecting progressive fracture connectivity. Rainy-season permeability coefficients reached 10−4–10−3 m/s, one to two orders of magnitude higher than those during the dry season. A substantial proportion of the observed displacement occurred during periods characterized by seasonal temperature fluctuations and rainfall-related hydrological changes. However, the available observations do not permit a quantitative separation of the contributions of freeze–thaw processes, rainfall infiltration, gravitational creep, and other driving mechanisms. Time-lapse TEM observations revealed substantial temporal variations in the resistivity structure of the landslide fracture zone. The development and spatial connectivity of low-resistivity anomalies were associated with seasonal hydrological changes, indicating the potential of repeated TEM surveys for characterizing subsurface moisture redistribution and fracture-zone evolution. However, the temporal resolution of the available TEM surveys does not permit identification of minute-scale precursory signals. The proposed framework provides quantitative visualization of fracture evolution and effective geophysical constraints for landslide stability assessment and early warning.