The COSY Project: verification of global seismic modeling algorithms

Progress in determining the details of the global 3-D seismic velocity structure requires the ability to accurately model seismic wave propagation (e.g., travel times, waveforms, etc.) through heterogeneous 3-D Earth models. While for spherically symmetric models (quasi-) analytical solutions are available for the verification of numerical algorithms, this is not the case for general heterogeneous models. It is therefore desirable to establish global 3-D test models and verified reference seismograms, which allow us to assess the accuracy of numerical algorithms quantitatively. Prior to a workshop held on this issue at the 1997 IASPEI Meeting, a 3-D test model was handed out to various groups and long-period synthetic seismograms were returned. This workshop was the initiation of the COmparison of global SYnthetic seismogram techniques (COSY) Project, which aims at establishing a WWW page (http://www.geophysik.uni-muenchen.de/COSY), where the test models and seismograms as well as some of the algorithms can be accessed. In this paper, we study the accuracy of and compare solutions from different numerical methods for a spherically symmetric model and the 3-D test model. The algorithms compared use the normal-mode method, the Direct Solution Method (DSM), a direct evaluation of the Greens function for spherically symmetric media (GEMINI), and the finite-difference (FD) method. Our 3-D test model is a perturbation to the spherically symmetric background model (PREM) based on a (scaled) temperature field from numerical modeling of mantle convection. The model displays many features in common with recent seismic tomographic images. We suggest that in addition to (future) 3-D reference Earth models, verified reference synthetic seismograms should be established for use by the seismological community.

@article{id76,
  author = {Igel, H. and Takeuchi, N. and Geller, R. J. and Megnin, C. and Bunge, H.P. and Clevede, E. and Dalkolmo, J. and Romanowicz, B.},
  journal = { Phys. Earth Planet. Int.},
  language = {en},
  number = {1-2},
  pages = {3-23},
  title = {The COSY Project: verification of global seismic modeling algorithms},
  url = {http://www.geophysik.uni-muenchen.de/{\textasciitilde}bunge/downloads/cosy.pdf
http://www.geophysik.uni-muenchen.de/{\textasciitilde}bunge/downloads/cosy.ps.gz},
  volume = {119},
  year = {2000},
}

%O Journal Article
%A Igel, H.
%A Takeuchi, N.
%A Geller, R. J.
%A Megnin, C.
%A Bunge, H.P.
%A Clevede, E.
%A Dalkolmo, J.
%A Romanowicz, B.
%J  Phys. Earth Planet. Int.
%G en
%N 1-2
%P 3-23
%T The COSY Project: verification of global seismic modeling algorithms
%U http://www.geophysik.uni-muenchen.de/~bunge/downloads/cosy.pdf
http://www.geophysik.uni-muenchen.de/~bunge/downloads/cosy.ps.gz
%V 119
%D 2000