The forward modeling of S-SKS and ScS-S differential travel time residuals sensitive to structure beneath a localized region of the central Pacific suggests the presence of two anomalous domains: first a broad zone which becomes thinner as it extends into the mid-mantle, where the S-velocity is reduced by -2 to -4%, and which is deflected to the South-East as it rises towards the surface; adjacent to it, a smaller domain, where the S-velocity is about 4% higher. These strong velocity anomalies are likely the results of chemical heterogeneity that may involve subducted material, and partial melting. Strong heterogeneity appears to extend, at least locally, well above D″, but the morphology of the anomalous domains is more reminiscent of localized rising or sinking currents rather than of a relatively uniform and thick geochemical reservoir. ¿ 2001 American Geophysical Union