Global models of surface wave group velocity

Measurements of group velocity are derived from phase-velocity dispersion c urves and modeled with global laterally-varying isotropic structure. Maps f or both Love and Rayleigh waves are created in the period range 35 s to 175 s. The data set of group-velocity measurements includes over 50,000 minor- arc observations and 5,000 major-arc observations. The errors in the measur ements are estimated by an empirical method of comparing pairwise-similar p aths, resulting in uncertainties which are 20% to 40% of the size of the ty pical measurement. The models are deter-mined by least-squares inversion fo r spherical harmonic maps expanded up to degree 40. This parameterization a llows for resolution of structures as small as 500 km. The models explain 7 0-98% of the variance relative to the Preliminary Reference Earth Model (PR EM). For the area of Eurasia, the group-velocity maps from this study are c ompared with those of Ritzwoller and Levshin (1998). The results of the two studies are in very good agreement, particularly in terms of spatial corre lation. The models also agree in amplitude at wavelengths longer than 30 de grees. For shorter wavelengths, the agreement is good only for models at sh ort periods. The global maps are useful for prediction of group arrival tim es, for revealing tectonic structures, for determination of seismic event l ocations and source parameters, and as a basis for regional group-velocity studies.