An efficient joint inversion strategy for 3D seismic travel time and DC resistivity data based on cross-gradient structure constraint

Joint inversion of different geophysical data based on cross-gradient structure constraint can improve the reliability of the imaging result. However, because different geophysical observations have varied sensitivities to the Earth medium properties, which are associated with different inversion systems, it is a big challenge to construct and resolve the joint inversion system. To solve the above problems, we propose a new joint inversion strategy by combining the model updates from separate inversions and cross-gradient structure constraint. This strategy first determines the model updates from separate inversions and then utilizes them to constrain the cross-gradient inversion system to get the new model updates. In this way, we can effectively implement the cross-gradient based joint inversion and realize the balance between fitting separate data types and increasing structure similarity between the two models. The new inversion strategy does not need to modify the individual inversion code to realize the joint inversion, making it much easier to conduct the cross-gradient based joint inversion. In addition, it also overcomes the difficulties in storing and inverting large joint inversion matrix. Based on the new strategy, for the first time we implement 3-D joint inversion of seismic travel-time and DC electrical resistivity data based on cross-gradient structure constraint. The test on a synthetic model shows that compared with separate inversions, the joint inversion method can effectively reduce the artifacts shown in seismic travel time inversion results and significantly improve the resolution of the resistivity inversion.