Equivalent Medium Parameters for Numerical Modeling in Media with Near-Surface Low Velocities
We have developed a methodology to discretize an isotropic velocity model with low velocities near the free surface for full waveform numerical modeling. The method modifies the near-surface minimum velocity in a given (original) model by replacing parts of the model with equivalent medium parameters (EMP). The discretized model (with EMP) has a higher minimum velocity and minimizes the difference between the seismograms evaluated for the original model and the model with EMP. The method is suitable for studies requiring full waveform numerical modeling with a limited frequency range (such as a finite-difference full waveform modeling in a sedimentary basin). The discretized model with EMP is set to match locally surface-wave velocities evaluated in the original model over the frequency range of interest. The difference in group velocity calculated for the original vertical profile and the vertical profile with EMP provides an estimate of the error due to the modification of the original model.
© 2002 by the Seismological Society of America. Manuscript received 1 April 2001. The authors are grateful to Luis Rivera for interesting insights during the development of this method. Special thanks go to Hiroo Kanamori who not only followed our progress but significantly helped with the determination of the error criterion. Dimitri Komatitsch greatly helped to make this manuscript readable and offered his experience to evaluate one of the numerical tests used in this article. We thank Václav Vavryčuk, Kim Olsen (reviewer), Ivan Pšenčík, Jeroen Tromp, Jascha Polet, Si-Dao Ni, John Etgen, and anonymous reviewer for their input when developing this method and preparing the manuscript. Many of the figures were made with Generic Mapping Tools software (Wessel and Smith, 1991). This research was supported by the Southern California Earthquake Center (SCEC). The SCEC is funded by NSF Cooperative Agreement EAR-8920136 and U.S. Geological Survey Cooperative Agreements 14-08-0001-A0899 and 1434-HQ- 97AG01718. The SCEC Contribution Number for this article is 524. This is Contribution Number 8820 from the Division of Geological and Planetary Sciences, California Institute of Technology.
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