To address safety problems caused by goaf and water accumulation in open-pit mines, the shallow three-dimensional seismic method and transient electromagnetic method were integrated and applied to detect the mining goaf distribution scope and the water accumulation conditions. In view of the special topographic conditions of an ultrashallow layer and high drop in an open-pit mine, we proposed utilizing bin homogenization and multidomain joint denoising to improve the reliability of seismic data. By using seismic-sensitive attributes to predict the goaf, the transient electromagnetic method was employed to further predict the water accumulation in the goaf. The results show that the shallow seismic method could clearly reflect the reflected-wave variation features of the goaf. The features of a junction between a normal seam and goaf vary obviously, and the prediction effect of the goaf boundary with high resolution is in line with the actual situation. Furthermore, taking the goaf scope prediction with the shallow three-dimensional seismic method as a base, targeted transient electromagnetic detection was deployed, with a detailed analysis of the survey-line repeated areas of the shallow seismic and transient electromagnetic methods. Making full use of the advantages of the shallow seismic and transient electromagnetic methods, we propose a reasonable data interpretation method in combination with the special topographic conditions of open-pit mines, which greatly improves the prediction effect of goaf and water accumulation conditions.

Nonstationary convolution models are widely used as the forward formula of nonstationary seismic reflectivity inversion (NSRI). This forward formula is determined by the convolution of a time-varying wavelet and reflectivity. Previous NSRI algorithms just focus on the estimation of reflectivity according to different sparse regularization strategies. The forward-operator, time-varying wavelet matrix is usually generated using a user-defined constant Q-value. However, the Q-value changes with time and space; therefore, inaccurate reflectivity inversion results will be yielded by the traditional NSRI method. In order to improve the accuracy of the inverted reflectivity, we propose a new forward-operator construction method based on the monotone relationship between the equivalent Q-value (Q_e) and centroid-frequency (CF). We first extract CF from the Gabor time-frequency amplitude spectrum of the seismic signal. Then, we can obtain Q_e through the CF-Q_e template. Hence, the blindness of selecting a Q-value is avoided and a more accurate forward operator can be constructed. Synthetic and field-data examples demonstrate that the proposed method provides a more accurate reflectivity estimation by constructing a more reliable forward operator. Furthermore, the enhanced reflectivity sections enable a clearer delineation of top and bottom interfaces of coalbed methane reservoirs, providing high-resolution seismic support for coal seam interpretation and subsequent mining planning.