Research on Identification of Underground Water Hazards in Coal Mines Based on Joint Magnetotelluric and Microtremor Detection

Underground water hazards are among the most serious concealed threats to safe coal mine production, yet their accurate spatial localization remains challenging when relying on a single geophysical method. This study proposes a joint detection framework integrating the magnetotelluric (MT) method and the microtremor survey method (MSM), and applies it to the Shaping Coal Mine in Lianyuan City, Hunan Province, China. The MT method was used to image the resistivity structure of water-bearing bodies at depths of 50–500 m, while the MSM delineated the shear-wave velocity structure of shallow-to-middle strata (0–300 m). A comprehensive identification criterion based on the spatial superposition of “low resistivity + low velocity” anomalies was established. The MT results identified low-resistivity water-bearing structures within the coal-bearing Ceshui Formation, while the MSM revealed reduced-velocity anomalies, some 30% below the background value of the host unit, associated with the Coal Seam No. 5 goaf and fault fracture zones. The two methods formed an effective overlapping detection zone at depths of 100–300 m, with anomalies distributed above the mined-out area and near the Sifangqiao reverse fault, showing strong correspondence with documented water seepage. Within this overlapping window the two independently inverted anomaly sets show a spatial coincidence, expressed as the intersection-over-union of their footprints, of more than 0.85, and the principal seepage points recorded in the roadways fall inside the jointly delineated anomalies. The framework is an integrated interpretation of two independent inversions rather than a mathematically coupled joint inversion, and it provides supporting geophysical evidence for water hazard prevention and control in geologically complex coalfields.