A study of Forward Models in Seismic Inversion

Abstract

Knowledge about the physcical parameters of the seafloor is often important information. This master s thesis looks at seismic inversion to find these parameters. The choice of forward model is highly emphasised. A seismic inversion has a number of variables which can be changed and altered to obtain a good result. The forward model will have a big impact on the results of the inversion. Both the time spent on the inversion, and which parameters the inversion will be best suited to estimate will be determined by the choice of forward model. An inversion code written in Matlab by Fredrik Helland is used. It uses genethic algorithms as optimization, and OSIRIS as forward model. This code is expanded to deal with several forward models and seafloor geometries. Testing of the inversion code shows that all the forward models serves different perposes. The ray tracing model is still at a consept level, but should be usable in the future when it runs a bit faster and can deal with more than 3 layers. The dispersion method and the wave number integration method both work well and the results show that using a combination of them might be the best choice if all the geoacoustic parameters of the seafloor is sought.