We have automatically measured phase dispersion and
arrival angles on seismograms from a database of over 100,000
digital records. The measurements are in the range 32s to
150s. This data set is inverted for global laterally
heterogeneous phase velocity structure. We have developed
theory for interpreting the measurements in terms of
anisotropic phase velocity.
2011 Update: Global Dispersion Model GDM52
We have extended the 1997 Ekström, Tromp, and Larson study
to shorter and longer periods, and including azimuthal
anisotropy. The results are published in the
Global Dispersion Model GDM52.
Some earlier results and links
We have calculated group velocity values from the phase
dispersion curves at a number of periods, and then
determined maps of
global group velocity.
These maps are isotropic models, up to degree 40 spherical
harmonics. We also compare this models to recent group
velocity models of Eurasia in Ritzwoller and Levshin (1998)
We have analyzed our dataset of
arrival angle measurenments to determine
azimuths of seismometers worldwide.
Our large data set of Rayleigh wave and
Love wave phase measurements has been inverted
for isotropic phase velocity maps,
expanded in spherical harmonics to degree 40.
An automated method for making measurements of arrival angle
has been developed.
We have developed a
complete ray theory for anisotropic
propagation of surface waves, including terms to predict
phase, arrival angle, and amplitude.
A comparison of ray perturbation theory to exact ray
theory shows that perturbation theory is sufficiently accurate
(for phase and arrival angle) for use in large scale inversions
for anisotropic phase velocity structure.
Maps of phase velocity which allow only isotropic structure
can be biased, predicting small scale isotropic structure in
place of true anisotropic structure.