Research On Models And Algorithms Of Geodesy And Geophysics Joint Inversion

Geodetic inversion is geodetic core that studies geoscience and also a branch that speculates on spatial change and evolution of physical state of interior medium in earth by deformation data measured. It is significant in theory and valuable in application to combine geodetic inversion with seismology and geophysics to study on geodynamics, deep-seated structural details of earth, the dynamical process of interior earth and material characteristics. Geodetic inversion is regarded by homely and abroad highly. Especially, crust deformation is natural related with earthquake. So it is a key task of geodetic inversion to research on the process and mode of warning signs of an earthquake, even to forecast an earthquake with interseismic and preseismic deformation measurement. Dislocation is a usual mode to study warning signs of an earthquake.The dislocation theory is researched systemically in the dissertation. The joint inversions with kinds of data based on dislocation are researched. Some usual algorithms are analyzed contrastively. Interval algorithm is discussed mainly. The interval Simulated Annealing algorithm is used to locate a local earthquake and jointly invert fault parameters with GPS and gravimetry in the west of Sichuan.The main research contents and new calculation methods in the dissertation are following:1. Research on dislocation modelThe changes of displacement, strain, tilt, gravity and crustal internal deformation due to dislocation are summarized systemically in the dissertation. Wrong Partial derivatives formulae of dislocation model in some papers are corrected in the dissertation. It is a contribution to researchers who use some methods based on partial derivatives of parameters, such as, the Least-Squared method. The correction perfect the dislocation theory2. Research on Joint Inversion modeJoint inversion with kinds of data is one of the keys of the dissertation. Some top-quality deformation data, such as GPS, leveling, gravimetry and InSar, are obtained by monitoring crustal movement. In fact, those data are output signals of responding to geodynamic process of the interior of earth. The responds to movements are different, but the medium is the same. So, joint inversion is a potential tool to analyze geophysical data.A kind of joint inversion that will invert the weight in the object function is proposed in the dissertation. Based on dislocation mode, the kind of joint inversion with simulated GPS, leveling and gravimetry data is used by twos or whole to invert the parameters of three-dimension fault model. In addition, this kind of joint inversion is also used to invert regional or local horizontal velocity with geodetic data, seismic data and geologic data, such as the Quaternary fault slip.3. Research on Inversion AlgorithmsResearches on joint inversion algorithms are another key of the dissertation. Inversion aims to get the minimum of the object function. This is an optimal question in mathematics. The classical methods, such as the Least-Squared method and Bayesian method with a prior information of parameter, need partial derivatives of parameters. In general, geodetic or geophysical model is very nonlinear, the derivatives are very complicated and even it is difficult to express them in formulae. So, recent years, some methods without partial derivatives are used widely.Some algorithms, such as Monte Carlo, genetic algorithm, Simulated Annealing algorithm, random cost method and interval algorithm, are compared in the dissertation. Thereinto, Monte Carlo, genetic algorithm, Simulated Annealing algorithm and random cost method are based on stochastic search. They can sometimes jump over local optimum and converge to global one, but they can't be successful every time because of their inherent stochastic nature. They have the same chance to converge to local and global optimum. So they can't be called whole global optimizations, but a global optimization oriented. Especially, interval algorithm is regarded as a whole global optimization in the dissertation. It is superior to other optimization methods in reliability and appraisal of results. And it is a method to find all global minimizers of a constrained nonlinear function with several variables. It is impossible to converge to a local minimizer for interval algorithm. It is concluded that interval algorithm is a reliable and efficient global optimization method.These methods are compared by inverting fault parameters with simulated gravimetry data base on dislocation mode. Several tests are made with every method. To the stochastic method, the different tests bring different results. If the true value of parameter is unknown, it can not be concluded which answer should be selected as inversion result. Simulated annealing method is better among the all stochastic methods. Interval algorithm can always converge to an interval including global optimum and the upper of approaching error is computed easily.To accelerate the speed of computation of interval algorithm, it is combined with simulated annealing method for the first time. And the new method is called interval simulated annealing method in the dissertation. The combination accelerates the computation speed and makes algorithm reliable and exact. This is a hybrid of stochastic search and exhaustive search.An improvement of interval Newton method is given in the dissertation. It corrects the unreliable part of prototype algorithm and makes the method more reliable and stable. Some examples show the application of it in solving nonlinear equations and global optimization.4. Research on Location of Near EarthquakeSeismic location is to decide the location of hypocenter and the time of earthquake occurrence. It is a basic question of seismology. The location result can disclose some important information about earthquake activities and the earthquake circumstance, thus, the earthquake mechanism and cause of occurrence will be known more. With the more development of digital observation technology, the more accurate location of hypocenter is needed. This is helpful to study hypocenterthe crustal structure and the crustal velocity model.The methods and principles of seismic location with IA-SA and classical Geiger method are introduced in case of homogeneous crust. The focus parameters of Shacheng earthquake in 1976 are inverted by the two methods respectively. The result of IA-SA is superior to the one of Geiger method according to some quantitative compares.5. Research on Geodetic Inversion of the Faults of the West of Sichuan Province Sichuan locates the southeastern of Qinghai-Tibet Plateau. There were many earthquakes historically. The intensity of seismic activities is the fifth in our country. Sichuan province is an important part of South-North Seismic belt. Xianshuihe fault locates the western Sichuan province. It is famous home and abroad and characteristic on intensive structural activities. In addition, Litang-Dewu fault locates the southwestern of Xianshuihe fault. They are researched in detail in the dissertation.Multipurpose researches were done in Xianshuihe fault broadly. According to its character of activity, Xianshuihe fault is divided into northwestern segment, Qianning-Kangding segment, Zheduotang segment and Moxi segment. The data used in the dissertation include relative gravimetry between 1996 and 2001 and GPS velocities between 1991 and 2000.Firstly, the two kinds of data is inverted individually by SA and IA-SA so as to compare their results.There are two projects to invert GPS. The one inverted all parameters of four segments if Xianshuihe Fault. Through the map of velocities, there are obvious differences on some points. Considering the big velocity of some points on southwestern of Xianshuihe fault, the second project is brought forward to invert Litang-Dewu fault synchronously. 7 parameters of every fault segment will be inverted, that is, the location of fault and strike are given some fixed values. According to value of object function, the results of IA-SA is superior to the ones SA. Therefore, the results of IA-SA are regarded as the inversion results with GPS data. The velocity measured is consistent with the one inverted.According to the maps of annual gravity changes isolines between 1996 and 2001, Xianshuihe fault is the boundary of plus isolines and negative isolines. This says the intensive activities of both sides of fault. So it is necessary to consider the action of fault activity to gravity changes. The inversion with gravimetry data resembles the second project of GPS inversion, that is, there are 7 parameters of every fault segment inverted. Still, the results of IA-SA is superior to the ones SA.At the end of the dissertation, a joint inversion with GPS and gravimetry data is done. Two projects are also given with the relatively weight ratio fixed to 0.5 or inverted. The all ten parameters of every fault are inverted by IA-SA during the two projects. The relatively weight ratio of gravimetry inverted is 0.314. The value of object function with the relatively weight ratio inverted is small than the one of another project. The results show that the project with weight ratio inverted is better and match the different kinds of data more rational.It can be summarized that Xianshuihe fault is mainly a left lateral fault. The northwestern segment has the most intensive activity with a strike slip 13mm/a. The strike slip velocity in middle segment is 4.9~6.9mm/a. But the strike slip velocity in southeastern, the Moxi segment, arrives at 8.28mm/a. Three dislocation components of Litang-Dewu fault is close to each other, and it has the maximum tensile components, 5.12mm/a, among all 5 fault segments.