Global Models of Surface Wave Group Velocity

Abstract

Ð Measurements of group velocity are derived from phase-velocity dispersion curves and 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 data set of group-velocity measurements includes over 50,000 minor-arc observations and 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). For the area of Eurasia, the group-velocity maps from this study are compared with those 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, for determination of seismic event locations and source parameters, and as a basis for regional group-velocity studies.

Lateral Variations of Rayleigh-Wave Dispersions in the Philippine Sea Region

“…From Fig. 11, it can be see that our results provide better patterns of velocity variation, when compared with geological configurations, than the results given by Ekström et al (1997) and Larson and Ekström (2001) for the Philippine Sea region. This can be also accounted for by the fact that a study on a regional scale is more suitable for the interpretation of regional velocity variations than that on a global scale.…”

“…11. Comparison of the group-and phase-velocity of this study and those of Larson and Ekström (2001) and Ekström et al (1997) at the 40-sec period.…”

“…To verify the better resolution of the 2-D regional velocity maps described in this study, we compare an example of the 40-sec group-and phase-velocity results with previous globalscale studies (Ekström et al 1997;Larson and Ekström 2001); see Fig. 11.…”

“…Their results suggest that the plate thickness in the West Philippine Basin (including the Ridges) is about 60 km while it is about 40 km in the Shikoku, Parece Vela and Active Marginal basins. Since 1995, tomographic inversion with huge high-quality dispersion curves has been extensively used to establish global-scale surface wave group-and phase-velocity maps (e.g., Ekström et al 1997;Larson and Ekström 2001). Regional-scale tomographic images of surface waves, such as in the Philippine Sea or China, have been also made to investigate their tectonics implications (e.g., Lebedev et al 1997;Nakamura and Shibutani 1998;Hwang 1999).…”

A global horizontal shear velocity model of the upper mantle from multimode Love wave measurements

“…Love and Rayleigh wave dispersion maps for the fundamental mode exist (e.g. Trampert & Woodhouse 1995Larson & Ekström 2001;Visser et al 2007;Ekström 2011;Pasyanos et al 2014) and Rayleigh wave maps exist for some higher modes (van Heijst & Woodhouse 1997, 1999Shapiro & Ritzwoller 2002;Beucler et al 2003;Visser et al 2007Visser et al , 2008. Less work has been done on inverting Love wave measurements for β h (z) models (Li & Romanowciz 1996;Mégnin & Romanowicz 2000;Zhou et al 2005) and most existing β h (z) upper-mantle models are constrained using only fundamental mode measurements.…”