Joint Inverse Study Of Gravity And Seismic Data For 2D Multi-density Interfaces Basing On Integration Of The Objective Function

Joint inversion of geophysical exploration are important means to explain, and can improve the accuracy of the inversion.This paper presented a new method of the joint inversion of gravity and seismic data ,which can invert multi-density interfaces at one time.The new method was based on the theories of jointting inversion of gravity and seismic data in addition to the conventional forward modeling and inverse modeling theories.Using the Visual Fortran 6.0 and Perl develop tool, a series of programs of forward modeling and inverse modeling were developed. The inversion result of models and actual data demonstrated that united inversion method for multi-density interfaces is effective and correct.At first, the paper studied the 2D dispersed models of multi-density interfaces and presented a formula that can compute the gravity anomalies of multi-density interfaces and. seismic traveltimes. We presented the Jacobian matrix of seismic traveltimes relative to the depth and speed ,and presented the Jacobian matrix of the gravity anomalies relative to density and the depth of interface. Studying the theory of generalized linear inversion, we eatablished the objective function of united inversion for 2D multi-density interfaces. In this paper, damped least square method to solve the objective function. The corresponding iterative inverse formula was presented at the same time.Secondly, we designed single-interface model and multi-interfaces model. In additional, hill models was also designed. According to the trials of single-interface models, the influences of Damping factor and weight coefficient parameters to the inversion result were analyzed. The paper also summarized the common principle for selecting these parameters in actual inversion. In addtional, the influences of seismic traveltime and gravity anomalies error to the inversion result were Discussed.Also, the influences of density and velocity error to the inversion result were analyzed.Compared diferance initial models, we inclued that influence of initial models to inversion result was not prominent. According to the trials of multi -interface models, we proved that the united inversion method was effectual to multi -interface models. According to the trials of hill models, the problem of only seismic traveltime inversion and only gravity anomalies inversion were compared. This proves the effect of the joint inversion.The inversion was done to the 1:5 high-precision gravity data and line 616 of horizontal stack travel-time profile of Southern Jiyang Depression.Nine interface were obtained from the inversion result, and the method of the joint inversion of gravity and seismic data was proved practicably and effectively.At last, the paper summarized some problem that existed and presented several advice for improving united inversion method.