ASA 124th Meeting New Orleans 1992 October

5aPAb6. Reasonable choices for material constants in seismic modeling.

J. H. Rosenbaum

1308 Castle Ct., Houston, TX 77006

The assumption that the earth is made up of homogeneous elastic layers, which can exhibit transverse isotropy and moderate constant-Q attenuation, leads to an effective method of modeling the response from a point source into a long spread of seismometer stations [J. H. Rosenbaum, Geophysics 36, 1276--1277 (1971)]. A difficulty experienced by users of such programs is the necessity of furnishing consistent elastic constants and absorption values for the formations. An extension of the long-wavelength-equivalent-medium theory [G. E. Backus, J. Geophys. Res. 67, 4427--4440 (1962)] to the anelastic case has been used to derive default options, which require minimal information from the user, appear reasonable for many earth materials, and reduce to a proper description for the case of isotropy. A very simple earth model demonstrates that parasitic modes are excited and the computations may become unstable when anelastic model parameters violate stability conditions or are inconsistent. [Work done at Shell Development Co.]