The relative behavior of shear velocity, bulk sound speed, and compressional velocity in the mantle: Implications for chemical and thermal structure

Abstract

Despite immense progress in imaging seismic velocity anomalies in the mantle over the past 15 years, we still know relatively little about their physical cause. One way to shed some light on this problem is to investigate the relative amplitudes of compressional and shear velocity anomalies in the mantle. Unfortunately, the amplitudes of velocity anomalies can be quite sensitive to the data sets and imaging techniques employed. It is therefore usually meaningless to take two models from the literature and do a simple comparison, In this paper, we consider joint modeling of P and S data sets and compare with some recent results from the literature. Some robust patterns are beginning to emerge which allow us to identify regions of the lower mantle which are anomalous. Such regions seem to be associated with large-scale upwelling in the mantle and may indicate chemical interaction with the core.