A new technique for making single-station phase velocity measurements
is developed and applied to a large number of globally recorded Raylei
gh and Love waves in the period range 35-150 s. The method is based on
phase-matched filter theory and iteratively suppresses the effect of
interfering overtones by minimizing residual dispersion. The model sur
face wave signal is described by its amplitude and apparent phase velo
city, both of which are parameterized in terms of smooth B-spline func
tions of frequency. A misfit function is constructed which represents
the difference between the model and observed waveforms, and the optim
al spline coefficients are estimated in an iterative misfit minimizati
on algorithm. In order to eliminate cycle skips in the measurements of
phase at short periods, the waveforms are first matched at long perio
ds, and the frequency range is gradually extended to include higher fr
equencies. The application of the algorithm to records from the Global
Seismographic Network, using earthquakes in the Harvard centroid-mome
nt tensor catalog, results in the determination of more than 50,000 hi
gh-quality dispersion curves. The observed variations in measured disp
ersion for pairwise similar paths are used to estimate realistic uncer
tainties in the data. Phase delays at discrete periods are inverted fo
r global maps of variations in phase velocity expanded in spherical ha
rmonics up to degree 40. A realistic resolution test indicates that st
ructures are well recovered up to at least degree 20. The new phase ve
locity maps explain 70-96% of the observed variance in phase residuals
, reflecting the high internal consistency of the dispersion measureme
nts.