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Application of simulated annealing to some seismic problems

University of British Columbia

Wavelet estimation, ray tracing, and traveltime inversion are fundamental problems in seismic exploration. They can be finally reduced to minimizing a highly nonlinear cost function with respect to a certain set of unknown parameters. I use simulated annealing (SA) to avoid local minima and inaccurate solutions often arising by the use of linearizing methods. I illustrate all applications using numerical and/or real data examples. The first application concerns the 4th-order cumulant matching (CM) method for wavelet estimation. Here the reliability of the derived wavelets depends strongly on the amount of data. Tapering the trace cumulant estimate reduces significantly this dependency, and allows for a trace-by-trace implementation. For this purpose, a hybrid strategy that combines SA and gradient-based techniques provides efficiency and accuracy. In the second application I present SART (SA ray tracing), which is a novel method for solving the two-point ray tracing problem. SART overcomes some well known difficulties in standard methods, such as the selection of new take-off angles, and the multipathing problem. SA finds the take-off angles so that the total traveltime between the endpoints is a global minimum. SART is suitable for tracing direct, reflected, and headwaves, through complex 2-D and 3-D media. I also develop a versatile model representation in terms of a number of regions delimited by curved interfaces. Traveltime tomography is the third SA application. I parameterize the subsurface geology by using adaptive-grid bicubic B-splines for smooth models, or parametric 2-D functions for anomaly bodies. The second approach may find application in archaeological and other near-surface studies. The nonlinear inversion process attempts to minimize the rms error between observed and predicted traveltimes.

Thesis/Dissertation

application/pdf

2009-06-25

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http://hdl.handle.net/2429/9599

Oceanography

University of British Columbia

UBCV

DSpace