Master thesis defense by Niels Fabrin Nymand

Title: Spectral element and the adjoint method in seismology - Modelling of discontinuous boundaries

Abstract: In this thesis I join spectral element modelling of seismic waves with the adjoint method to try and reproduce discontinuous boundary layers from seismic signals. The adjoint method is a highly efficient way of generating model gradients to be used in steepest descent type inversion algorithms. A series of simple models are made to demonstrate how the adjoint method can be used to model sharp bound- aries, such as faults, from seismic data. The results show that the method is able to locate and horizontally delimit sharp contrasts not accounted for by the prior model. The method is also tested on a more complex model, based on the seis- mic survey of North Viking Graben [Keys et al., 1998], where the success of the method does in part rely upon good prior model estimations. Spectral element modelling has the advantage of being able to accurately hon- our complex model geometry with a well designed mesh. Based on a seismic flat- tening algorithm I present a simple approach to generating a finite element mesh to be used with the spectral element software SPECFEM2D [Komatitsch et al., 2012].

Supervisor: Klaus Mosegaard

Censor: Thomas Mejer Hansen (AU)