Strong seismic scatterers near the core-mantle boundary west of Mexico

PKP phases observed in Japan show strong precursors with clear onsets for e arthquakes that occurred in south America. The onset times of the PKP precu rsors can all be explained by existence of seismic scatterers in the lowerm ost 100 km. of the mantle west of Mexico, within an area of 200 km x 300 km . Forward modeling of PKP precursor amplitudes indicates that a P-wave velo city variation of at least 6% is required to explain the large amplitudes o f the observed PKP precursors, suggesting that the core-mantle boundary reg ion beneath west of Mexico is a highly anomalous region characterized by st rong seismic scatterers.