Abstract:
The discrimination between chemical and thermal heterogeneity in the Earth's mantle remains one of the most important and challenging questions to be answered by observational and theoretical geophysics. To answer this question requires a thorough knowledge of the ratio between compressional and shear velocity anomalies. We describe results of a joint inversion for compressional and shear velocity in the mantle using a large and diverse data set consisting of traveltimes, complete waveforms and surface wave dispersion measurements. A horizontal tessellation consisting of 362 spherical splines is used to parametrize the model, which is approximately equivalent to a spherical harmonic of degree 18 in resolution. The model contains peak variations (from PREM) of up to +-7 per cent in S velocity and +-2.5 per cent in P velocity in the upper mantle. These variations decrease to +-1.5 and +-0.6 per cent, respectively, at 1000 km depth and reach +-2.5 and +-1.0 per cent, respectively, in the D'' region.
