Simultaneous Traveltime Inversion In Complex Isotropic/Anisotropic Medium Using Multi-Phase Arrivals

With the increased demand and continuous exploitation of oil and gas and mineral resources,as well as the intensive study of crustal and mantle structure, the relatively low spatialresolution of traveltime tomography is becoming an increasingly serious problem. Therefore,the main research works we have done in this thesis are aimed at how to improve theresolution of the seismic traveltime tomography.From a point view of basic theory, considering the impact factors on the tomographicresolution, for example, the ray high frequency assumption, ray coverage rate, crossing rayintersecting rate of different phases, the complexity and anisotropic properties of media, weattempt to improve the resolution in several ways: by introducing the multi-phase traveltimedatasets, it is possible to increase the ray density and crossing ray intersecting rate; byintroducing the concept of Fresnel Volume ray, it is constructive to overcome the drawback ofray high frequency assumption; by introducing the concept of phase and group velocity ingeneral anisotropic medium, it is able to avoid of week anisotropic assumption.For the forward modeling method, it is designed not only to work on the rectangularcoordinate system, but also on the Spherical coordinate frame to conduct seismic traveltimetomography locally, regionally and globally, we first put forward a multistage irregularshortest path method for multiple arrival tracing, and evaluate its computational accuracy andefficiency. The results show that the multistage irregular shortest path method has theadvantages in terms of global solution, numerical calculation stability, high calculationaccuracy and fast computation speed. Therefore, we firstly extend the functional of themultistage irregular shortest path method to the Spherical coordinate frame, and then to theFresnel Volume ray tracing and finally to the ray tracking in the anisotropic medium, whichholds the same advantages as in the rectangular coordinate system. So the multistage irregularshortest path method can yet be regarded as a preferred forward modeling algorithm in theseismic traveltime tomography.For the inversion method and technique, we mainly discuss the constrained, dampedleast squares problem solved by the conjugated gradient method, the subspace inversionalgorithm and the trade off and normalization between different classes of model parameters.Based on two inversion solvers, we combine them with the above forward modelingalgorithms to form four different traveltime tomography methods including:(1)simultaneously invert two types of model parameters (velocity and source location, or velocity and reflector geometry) by using multiple traveltimes both in the Cartesiancoordinate and the Spherical coordinate;(2) simultaneously update three classes of modelparameters (velocity, source location and reflector geometry) with multiple traveltimes both inthe Cartesian and Spherical coordinates;(3) simultaneously invert for velocity and reflectorgeometry by using multi-phase Fresnel Volume rays;(4) simultaneously update multipleelastic parameters in the general anisotropic medium by using multi-phase traveltimesdatasets.The numerical tests demonstrate that it is possible to effectively improve the spatialresolution by using the multi-phase traveltime datasets. And furthermore, all the simultaneoustraveltime inversion methods, such as, two or three model parameter inversion both in theCartesian coordinate and the Spherical coordinate, simultaneous inversion by using theFresnel Volume rays, and simultaneous invert multiple elastic parameters, by using multipletraveltimes, are practical and efficient ways to conduct traveltime tomography.In summary, the main innovative achievements in this thesis include:(1) using themulti-phase traveltimes datasets, we put forward a simultaneous inversion method for two andthree types of model parameters updated, which works on both in the Cartesian coordinateand the Spherical coordinate;(2) considering the width of seismic rays with differentfrequencies, we develop a simultaneous inversion method for velocity and reflector geometryupdated by using multi-phase Fresnel Volume rays;(3) making use of the multiple traveltimes,we establish a simultaneous inversion method to update multiple elastic parameters in generalanisotropic medium.