Experimental study on joint inversion of water conducted karstic collapse column based on mine TEM and seismic exploration

Karstic collapse column seriously threatens mine safety. Mine TEM and seismic exploration are two key widely applied methods for a practical karstic collapse column detection. Mine TEM is sensitive to water abundance and seismic method has high spatial resolution. To utilize the advantage of each method,the joint inversion of mine TEM and seismic exploration is proposed. First,based on the mirror 2D resistivity model and the 1D TEM whole space forward algorithm,the mine Pseudo-2D TEM inversion algorithm is proposed. The mine Pseudo-2D TEM inversion algorithm fulfills the joint inversion requirements of 2D model and cost-effective calculation time. Then,through removing the seismic forward term from the conventional joint inversion objective function (only preserving the seismic impedance model parameters in the cross gradient term),a unidirectional cross-gradient joint inversion algorithm is formulated. The seismic impedance model constrains the TEM inversion while the resistivity model does not constrain the seismic inversion in the unidi-rectional cross-gradient joint inversion. Seismic impedance inversion can be done by commercial software,and TEM inversion is based on the mine Pseudo-2D TEM inversion algorithm. Furthermore,the interpolation of seismic impedance model is proposed to achieve the match of seismic and TEM model grids. The clustering and segmentation of seismic impedance model based on K-means algorithm is proposed,which eliminates the secondary structure changes in the seismic impedance model and increases the stability of joint inversion. Finally,a model with a water conducted karstic collapse column is built,a 3D mine TEM simulation and a 3D seismic simulation are carried out. Independent inversion and joint inversion are calculated. Results show that joint inversion recovers both the shape and the electrical characteristics of the theoretical model. Joint inversion results not only have a high spatial resolution but also detect water abundance,which is better than independent TEM and seismic inversion results. Different from the traditional joint inversion method mainly used in a large scale target detection or shallow surface imaging,the unidirectional cross-gradient joint inversion based on mine TEM and seismic is reliable for the detection of targets with small scale and large depth.