Application of the ESPAC method based on the detection of goaf in a mid-deep coal mine

Abstract Water-rich goaf constitutes a primary hazard factor in coal mines, potentially triggering mine instability and ground subsidence. To detect water-rich goaf efficiently, economically, and non-destructively, the extended spatial autocorrelation (ESPAC) method was applied to perform microtremor surveys in the goaf of the mid-deep sections of the Renjiazhuang coal mine in Ningxia. Microtremor signals were obtained using a linear array, and the 2D distribution of subsurface shear wave velocity was inverted and verified against borehole data. The results showed that in the depth range of −200 to −600 m, the low-velocity zone (500–1500 m/s) is closely related to the fissure development and water-rich area, revealing the spatial distribution of hidden disaster-causing factors in the subsurface. Three low-velocity anomalies within the profile were successfully identified by microtremor probing and combined with borehole drainage validation, confirmed the presence of standing water within these anomalous areas. Enhanced application scope and depth of ESPAC methodology in coal mine water-rich goaf detection have been achieved, establishing comprehensive technical support and theoretical frameworks for subsequent water-rich zone risk assessments and mine safety monitoring systems.