The core-reflected phase ScP is a sensitive probe of the properties of an ultralow velocity zone (ULVZ) at the base of the mantle. In synthetic experiments, a ULVZ with large depressions in P and S velocities results in ScP having two diagnostic precursors and one later arrival, whose timing depends on ULVZ VP,VS, and thickness. Amplitudes of the additional arrivals can be large if ULVZ shear velocity has extreme reductions, such as 30% and greater. Some data examples are presented for southwest Pacific events recorded at short period and broadband arrays in Hawaii, which show evidence for a ULVZ. Resolving all three additional arrivals will help in addressing the strength and ratio of VS and VP reductions in ULVZ, and thus the issue of partial melt. ¿ 1999 American Geophysical Union