ISSN:
1365-246X
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Geosciences
Notes:
We present the results of global measurements of spheroidal and toroidal fundamental mode eigenfrequencies as well as fundamental spheroidal mode attenuation made from a data set consisting primarily of records from the Geoscope network. Data processing includes variable filtering and account is taken of higher order effects along the dispersion branch. Local frequency and attenuation maps are first obtained, as a function of angular order, by a regionalization scheme based on the introduction of a correlation length. In a second step, after correction for shallow-layer effects, shear velocity maps at different depths in the mantle are obtained by simultaneous inversion of spheroidal and toroidal local frequency maps. The results confirm the correlation of shear velocity with large-scale tectonic features in the first 200 km of the mantle. Below that depth, the maps are dominated by a degree-2 pattern whose power is peaked around a depth of 300 km, shallower than inferred in the first 3-D global studies of the upper mantle, and correlated with a degree 2 in attenuation, thus confirming the results of our earlier study of degree 2 in the upper mantle. We also report estimates of spherically averaged eigenfrequencies for fundamental spheroidal and toroidal mode branches.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1365-246X.1990.tb00758.x
