This thesis concentrates on a shape based approach for seismic full waveform inversion, especially a novel level set based shape estimation method for elas- tic waveform inversion. Full waveform inversion is a numerical data processing technique aiming at the reconstruction of subsurface structure of the earth using collected seismic reflective data. However, traditional techniques using an acous- tic or Helmholtz wave equation as forward model are faced with the limitation of using simulated non-elastic wave data to numerically fit elastic waveform data, which is physically incorrect and practically prone to obtaining wrong estimates; the correct scheme for modelling seismic waves is using an elastic wave equa- tion. We construct an elastic waveform inversion algorithm using a symmetric- hyperbolic scheme, and a time-reversal adjoint-state method; in addition, we introduce a Sobolev gradient method as a regularization method, with the goal to smooth the gradient function and thereby obtain more regular boundaries of the reconstructed shapes. However, the procedure of elastic waveform in- version is a multi-parameter estimation, which will lead to the numerical error of Ã¢ÂÂcross-talkÃ¢ÂÂ; this phenomenon is particularly severe in high-contrast situations and irregular shape boundary reconstruction problems, as expected to face in salt dome estimation problems. Therefore we introduce a shape based method using a level set technique to tackle specific seismic reconstruction problems, instead of more traditional pixel-based schemes. We also introduce a stochastic gradient descent method as an alternative to traditional gradient line search techniques for level sets, in order to increase efficiency and to avoid certain local minima in large-scale inversion problems. In addition, we introduce an additional inte- grated internal-value reconstruction scheme; this will prove to be an interesting and possibly necessary expansion of the shape based approach in order to deal with more realistic 3D seismic reconstruction problems.
|Date of Award||31 Dec 2019|
- The University of Manchester
|Supervisor||Oliver Dorn (Supervisor) & Sean Holman (Supervisor)|
SHAPE BASED METHODS FOR SEISMIC FULL-WAVEFORM INVERSION
Wu, Y. (Author). 31 Dec 2019
Student thesis: Phd