HR: 0800h
AN: S31B-1044    [Abstracts]
TI: Seismic Applications of the Fast Marching Method: Traveltime Prediction in Complex Layered Media and 3-D Tomographic Imaging
AU: Sambridge, M
EM: malcolm@rses.anu.edu.au
AF: Research School of Earth Sciences, Australian National University, Canberra, ACT 0200 Australia
AU: * Rawlinson, N
EM: nick@rses.anu.edu.au
AF: Research School of Earth Sciences, Australian National University, Canberra, ACT 0200 Australia
AB: The accurate prediction of seismic traveltimes is required in many areas of seismology, including the processing of seismic reflection profiles, earthquake location, and seismic tomography at a variety of scales. We present two seismic applications of a recently developed grid based numerical scheme for tracking the evolution of monotonically advancing interfaces, via finite difference solution of the eikonal equation, known as the fast marching method (FMM). Like most other grid-based eikonal schemes, FMM can only locate the first-arrival phase in continuous media; however, unlike other schemes, it combines unconditional stability with rapid computation. The first application of FMM that we consider focuses on the prediction of multiple reflection and refraction phases in complex 2-D layered media. By treating each layer that the wavefront enters as a separate computational domain, we show that sequential application of FMM can be used to track phases comprising any number of reflection and transmission branches in media of arbitrary complexity. We also show that the use of local grid refinement in the source neighbourhood, where wavefront curvature is high, significantly improves the accuracy of the scheme with little extra computational expense. The second application of FMM that we present is in the context of 3-D teleseismic tomography. We show that FMM can rapidly and robustly calculate two point traveltimes from an impinging teleseismic wavefront to a receiver array located on the surface, despite the presence of significant lateral variations in wavespeed in the intervening crust and upper mantle. Combined with a rapid subspace inversion method, the new FMM based tomographic scheme is shown to be extremely efficient and robust. For example, an iterative non-linear teleseismic tomography problem involving nearly 10,000 unknowns and 5,938 ray paths is solved in less than 10 minutes on a 1.6 GHz Opteron PC running Linux.
DE: 8180 Tomography
DE: 7260 Theory and modeling
DE: 7203 Body wave propagation
DE: 7205 Continental crust (1242)
DE: 7218 Lithosphere and upper mantle
SC: Seismology [S]
MN: 2004 AGU Fall Meeting