Niels Bohr Institute > Calendar > 2009 > Specialeforsvar Thoma...

Receiver function modeling

Modeling local subsurface velocity structures using multiple diverse algorithms

Supervisers: Klaus Mosegaard and Trine-Dahl Jensen

Specialeforsvar: Thomas R. N. Jansson 

Receiver function analysis is a seismic method utilizing that fact
that seismic P-waves impinging on a subsurface boundary will result in 
refracted and reflected P and S-waves. The generated waves are only 
the result of the local structure and by deconvolution the local 
effect can be isolated in a data set called the receiver function.
Reconstructing the local velocity-structure by comparing the observed 
receiver functions with synthetically generated receiver functions is 
usually regarded as a highly non-linear inverse problem.

In this thesis I will apply four different algorithms to recreate the 
subsurface velocity structure from a synthetic data set as well as 
data collected in Greenland. The algorithms are: Uniform search, the
Metropolis algorithm, Neighborhood search and the Levenberg-Marquardt 
algorithm.

Overall, the algorithms were successfully in reconstructing 
the synthetic data. In the Greenland data set the algorithms generated 
models indicating a low velocity layer which is most likely an
artifact of the difference between the wavelet used in the forward
algorithm and the wavelet embedded in the data. This problem affected 
all the algorithms. For the Greenland data only the Metropolis and the 
Levenberg-Marquardt algorithm found reasonable models. It was also
concluded that the Uniform search and the Neighborhood algorithm do 
not perform well in high dimensional problems.