The short-period vertical-component data from the Fiji Is. earthquakes recorded by three seismological networks in Japan are analysed to investigate short-wavelength lateral heterogeneities in D″ layer. A double-array stacking method, which allows us to combine event and receiver arrays, is applied to the records of each network. Three regions in the D″ layer sampled by the three networks are located at horizontal intervals of a few hundred kilometers. In all three regions, the D″ reflectors are detected. The height of the D″ reflector above the CMB, which is estimated by the differential travel time between PdP (D″ reflection) and P, changes from 270 km to 170 km. This result may suggest that some strong short-wavelength lateral heterogeneities exist in the D″ layer beneath the southwestern Pacific. ¿ 1998 American Geophysical Union