| In the course of roadway excavation,geological anomalies such as ancient river erosion zone and fault fracture zone are often encountered,which seriously threaten the safety of roadway excavation.Therefore,it is necessary to carry out advanced detection during roadway excavation to ensure efficient and safe roadway excavation.At present,seismic and transient electromagnetic are two important advanced detection techniques commonly used to ensure the safety of roadway tunneling.However,due to the multi-solution of geophysical problems and the limitation of single detection technology,the conventional advanced detection methods of roadway appear the problems of multi-solution and large detection anomaly range in data inversion.In view of the problems existing in data inversion with single detection method,it is of great significance to study the joint processing method of seismic and transient electromagnetic data.In this paper,a seismic full waveform and transient electromagnetic joint inversion method based on cross gradient constraint is studied.In the inversion calculation,the common geological model is inverted jointly by constructing the relation through the structural similarity of various geophysical data.In order to simplify the calculation,this paper deduced the to join the single inversion formula of cross gradient function,separate two inversion procedure,and in the process of building a full waveform inversion objective function formula to get rid of transient electromagnetic data forward,retention model constraint of transient electromagnetic inversion formula of cross gradient constraint based seismic waveform and all transient electromagnetic joint inversion of the objective function,Thus the joint inversion of the two is realized.The basis of joint inversion is single inversion,so single inversion should be done first.Single inversion consists of forward and inversion.In this paper,Hankel transform is used to solve the first-order Bessel function in the frequency domain for transient electromagnetic forward modeling,and cosine transform is used to realize time-frequency conversion.Then one-dimensional transient electromagnetic inversion is carried out based on simulated annealing,and least-squares quasi-two-dimensional inversion is carried out by simulated annealing inversion model,which greatly improves the accuracy of single inversion.Seismic wave equation forward modeling in time domain can well simulate the energy attenuation of seismic wave passing through medium.The forward analysis of the acoustic wave equation uses the form of five-point central difference to discretize and solve the wave field response,and the inversion uses the iterative solution of the velocity model based on the steepest descent method,which can make the results converge quickly.Finally,two groups of models are designed,the model is calculated,and the results are compared and analyzed.Through numerical simulation of two groups of models with different structures,the inversion results show that the joint inversion is better than the single inversion,and the boundary shape of the model can be well restored,the resolution can be improved,and the false anomalies of geophysical inversion can be suppressed.Because of the limitations of existing computing conditions and algorithm selection,there are still some problems to be solved in improving the efficiency and field application of seismic full waveform and transient electromagnetic data joint inversion,which mainly include inversion method selection,algorithm parallel calculation and field data processing optimization.Further research is needed.Figure 52 Table 3 Reference 103... |
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