Chaos Genetic Algorithm-based Magnetotelluric Deep Inversion

There are many good qualities in MT inethods,such as no artifical electromagnetism source requiring instead of crude electromagnetism sources which vary with time,lower cost,quite deep exploring depth,no influence shielding by high resistance strata,high resolving power on low resistance strata and so on.It has been widely applied in deep mother earth structure researching,oil and natural gas exploring,terrestrial heat field exploring , earthquake forecasting and researching. Inversion is one of the key taches in MT. Aiming at traditional methods' depending on initial model and having no sensitive strata, the Chaos Genetic Algorithms (CGA) are the first applied in MT inversion in this article. By analyzing the theory of CGA,some improved methods are putted forward there and the sofeware blocks of CGA based on Matlab6.5 have been developed.Genetic Algorithms(GA) are random searching methods similar to natural selec- tion and natural genetic mechanism,which are advanced by professor J.H.Holland in 1975. It is simple, general,quite robust and fitting for parallel processing, and has been successful applied in widely fields in the past 20 years. GA has such good qualities as no differential coefficient requiring, no local linearization,low request for initial mo- del and so on. But GA is helpless in dealing with the optimization of many parameters which have big zones. CGA is the integration of GA and chaos optimizing, which has good qualities of the two. This article has done material analyse in CGA and some simulatings have been done by computer there, the compares of several Algorithms in inversions have also been done there, the elementary results as follows:(1) Both CGA and GA have the ability of globe optimizing, but CGA is more powerful.(2) Both the convergence speeds of CGA and GA are much slower than the classic linear methods, but their speeds after improved are acceptable, and the convergence speed of CGA is faster than that of GA.(3) It helps to increase the speeds and the precision of inversion ifwe use both the CGA and classic linear methods at the same time or integrate them.