Seismic Reflection Tomography From Travel-time And Its Gradient Data

The conventional reflection travel-time tomography needs to pick the travel-time of successive seismic reflection event and create the corresponding relation between reflector and event, which is a very hard work for low signal-to-noise ratio data. In order to solve this problem, the introducing of gradient of event in travel-time tomography is a current developing direction. So we research the reflection tomography from travel-time and its gradient data. The main research work includes: The study on automatic picking of travel-time and gradient based on local slant stack; The study on the creation of smooth velocity model based on Cubic B-spline; The study on the ray tracing in heterogeneous media based on normal ray equations; The study on the calculation of inversion matrix based on the paraxial theory; The study on the prior information constrained joint inversion of multi data parameters and multi model parameters.Based on the research work above, the programs of reflection tomography from travel-time and gradient are developed. The main function includes the automatic picking of travel-time and its gradient, ray tracing in continuum model, the computation of travel-time and its gradient, and joint inversion with travel-time and its gradient. The picking package realizes the quick automatic picking of travel-time and its gradient by seeking the locally coherent event of data. This package can also realize the manual correction and quality control on the interactive interface. The inversion package which combines local optimization algorithm and multi-scale joint inversion algorithm, using travel-time and its gradient as input data, realizes the stable and effective inversion process.The main characteristic of the method is the using of reflection travel-time and its gradient simultaneous, so instead of successively picking of travel-times of event in a wide range of source-receiver offset, only those fewer travel-times and gradients of locally coherent event which can be easily recognized are picked, and the manual determination of the reflecting interface of corresponding event is also avoided, which has important and practical value to the processing of low signal-to-noise ratio data. In the meantime, the introducing of gradient of travel-time can also better constrain the model parameters, reduce the multiplicity and improve the reliability of inversion. The experiment on synthetic data and real data shows that the seismic reflection tomography from travel-time and its gradient is fast and stable when executing, and could obtain much better macro-velocity model which is the base of migration imaging.