G. Laske et al., FREQUENCY-DEPENDENT POLARIZATION MEASUREMENTS OF LONG-PERIOD SURFACE-WAVES AND THEIR IMPLICATIONS FOR GLOBAL PHASE-VELOCITY MAPS, Physics of the earth and planetary interiors, 84(1-4), 1994, pp. 111-137
Surface-wave dispersion maps provide important constraints on global m
odels of shear-wave velocity structure. Current surface-wave dispersio
n maps show significant differences from researcher to researcher, and
it is clear that further work is required. In addition to dispersion
data, polarization measurements obtained from long-period (100 s or mo
re) three-component recordings from the various global networks can al
so be used to constrain dispersion maps. The off great circle propagat
ion of the surface-wave packets is relatively easy to interpret within
a ray-theoretic framework, and provides sensitivity to higher-order s
tructure. The polarization angles as a function of frequency are readi
ly measured using a multi-taper technique, which also has the benefit
of providing an error estimate for the measurements. Application of th
e technique to three-component seismograms from the global GEOSCOPE ar
ray reveals large deviations from great circle propagation (up to 15-d
egrees- for low-orbit Love waves and 10-degrees for Rayleigh waves in
the frequency band 5-12.5 mHz). On a more regional scale, an analysis
of seismograms from the German Regional Seismic Network (GRSN) reveals
even larger, strongly frequency-dependent deviations from great circl
e propagation in the frequency range 10-50 mHz.