Upper mantle models from ‘pure-path’ dispersion data

Abstract

‘Pure-path’ phase and group velocities of mantle Rayleigh waves in combination with mantle Love wave velocities and worldwide averages of free oscillation data are used to derive upper mantle models with the smallest possible number of parameters. The shear-velocity solutions between the crust-mantle boundary and 400 km appear to be unique for an assumed set of averaging lengths, despite the fact that the density solutions are nonunique over the same depth interval. Oceanic models are characterized by a well-developed low-velocity zone. For the set of data used in this study, the thickness of the oceanic lithosphere proves to be a critical parameter that influences the density solutions. If the thickness of the lithosphere is 80 km or less, a reversal in density distribution is necessary to explain the data. If the thickness is 100 km or greater, the densities between 10 and 400 km can be represented by a single average value. The shield data do not require a low-velocity channel when the velocity in the lid is 4.60 km/sec or less, but they do require a low-velocity channel for higher Sn velocities. The characteristic feature of tectonic models is high shear velocity between 200 and 400 km (>4.80 km/sec). This feature could be explained by the thrust of oceanic lithosphere under tectonic regions.