Integrated Geophysical Study of Geodynamics and Deformation Zones in an Undermined Rock Mass

Abstract: Comprehensive engineering and geophysical assessment of undermined rock masses is crucial for ensuring industrial safety and structural stability in mining regions. This study focuses on a site within the Berezovskoye gold ore deposit (Ural region, Russia), which was subjected to intensive shallow underground mining (up to 50 m depth) from the 18th to the early 20th centuries. This historical activity left numerous undocumented minor shafts and illegal artisanal workings. To localize hidden hazardous zones, electrical resistivity tomography (ERT) was initially deployed, revealing a distinct geoelectric anomaly at a depth of approximately 10 m, interpreted as a loosening zone associated with an abandoned horizontal working. Seismic surveying verified these data, confirming a local zone with reduced soil elastic properties via Poisson's ratio analysis. Building upon these findings, radon emanometry was applied over a 20×35 m grid (40 measurement points spaced 5×5 m) directly above the discovered anomaly to evaluate geodynamic processes and map the spatial boundaries of the deformation zones. Soil air radon volume activity (RVA) was measured using an RGA-500 alpha-counter from 0.8-meter-deep boreholes. To isolate the geodynamic component, the measured RVA values were normalized based on homogeneous geochemical and hydrogeological conditions. Furthermore, the ratio of radon (²²²Rn) and thoron (²²⁰Tn) isotopes was analyzed using delayed measurement techniques to distinguish and map specific zones of tensile and compressive deformations. The compiled geodynamic zonation maps demonstrated that anomalies of normalized RVA values spatially correlate with the locations of abandoned vertical mine workings. This confirms the high efficiency of the integrated geophysical approach for localizing hidden deformation zones in historically undermined areas.