Two Dimensional Joint Inversion Of Magnetic And Magnetotelluric Data

Traditional geophysical methods are magnetic, electric, gravity, seismic,logging and radioactive, different geophysical method interpret the subsurface structure by inverse different petrophysical properties. Joint inversion is a method of inverting different geophysical data together and finding the similar of the geological structure by petrophysical approach or structural approach. Therefore, Joint inversion is a new method different from the geophysical methods before. It is no longer observes the geological structure from a single petrophysical property but inverse the same geophysical model through the relationship of different petrophysical properties and geometric parameters. Joint inversion overcomes the limitation of single geophysical method and the problem of multiple solutions. It is the inevitable direction of the development of geological interpretation.Through the study and analysis of the most popular geophysical joint inversion methods in recent years, and take into account the susceptibility is used in the magnetotelluric inversion, we centered on magnetic and magnetotelluric data and performed joint inversion of the two methods.First of all, basic research works on magnetic 2-D inversion and magnetotelluric 2-D inversion was performed. About magnetic prospecting, we calculate the magnetic anomaly through the analytic solution, and inverse the susceptibility with smoothness constraint and logarithmic barrier method. The objective function not only includes data fitting difference, but also includes the model’s smoothness and the logarithmic term, so it can not only reduces the multiple solutions, but also avoids the susceptibility little than zero. About magnetotelluric prospecting, we using finite difference method to solve forward problem, we also joined the model’s smoothness term into the objective function so that the objective function constraint the model more, the inversion was performed by conjugate gradient method which greatly improving the operation efficiency and reducing the operation timeSecondly, we developed a 2-D joint inversion algorithm of magnetotelluric andmagnetic data on the base of cross-gradient theory proposed by Gallardo and Meju. In the inversion, using the central differences to discrete the cross-gradient which can add constraints on the boundary, and applied the susceptibility into the magnetotelluric inversion, make the inversion more reliable.Lastly, we designed some theoretical models for joint inversion. From the experiments results, we can know that the cross-gradient constraints can make the susceptibility and resistivity to constrain each other, our joint inversion algorithm will make the results more reliable and accurate than single geophysical method, which verifies the validity of our joint inversion algorithm.