Mapping structures on the core–mantle boundary using Sdiff postcursors: Part II. Application to the Hawaiian ULVZ

Abstract

SUMMARY We present a new data set of nearly 100 earthquakes which show clear evidence of the Hawaiian ultra-low velocity zone (ULVZ) in the S core-diffracted phase (Sdiff), representing the most comprehensive Sdiff data set of a ULVZ to date. Using a Bayesian inversion approach, as outlined in Martin et al., and a subset of the data set, we characterise the 2-D morphology and velocity of the Hawaiian ULVZ. The results suggest that the ULVZ is smaller than previously estimated, with an elliptical shape, and oriented along the direction of the large low-shear velocity province boundary. Using forward modelling, we infer that the ULVZ has a height of 25 km and shear velocity reduction of 25 %.