Larson, E.W.F. and G. Ekström, Global Models of Surface Wave Group Velocity, Pure Appl. Geophys. 158 (8), 1377-1400, 2001.
Also published as part of Monitoring the Comprehensive Nuclear-Test-Ban Treaty: Surface Waves (Volume 7 in the PAGEOPH CTBT Special Issue). Dr. M Ritzwoller and Dr. A Levshin are the editors for this special volume.
Measurements of group velocity are derived from phase velocity dispersion curves and are modeled with global laterally-varying isotropic structure. Maps for both Love and Rayleigh waves are created in the period range 35 s to 175 s. The dataset of group velocity measurements includes over 50,000 minor-arc observations and over 5,000 major-arc observations. The errors in the measurements are estimated by an empirical method of comparing pairwise similar paths, resulting in uncertainties which are 20% to 40% of the size of the typical measurement. The models are determined by least-squares inversion for spherical harmonic maps expanded up to degree 40. This parameterization allows for resolution of structures as small as 500 km. The models explain 70--98% of the variance relative to the Preliminary Reference Earth Model (PREM). The group velocity maps from this study are compared for the area of Eurasia with the maps of Ritzwoller and Levshin [1998]. The results of the two studies are in very good agreement, particularly in terms of spatial correlation. The models also agree in amplitude at wavelengths longer than 30 degrees. For shorter wavelengths, the agreement is good only for models at short periods. The global maps are useful for prediction of group arrival times, for revealing tectonic structures, and as a basis for regional group velocity studies.
The coefficients of the group velocity models and images of the models are also available.