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 comprehensi ve Sdif f 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 pre viousl y 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 %.