Converted phases have been identified in the P-wave coda of teleseismic seismograms from a single large (MW 6.8), deep (360 km) earthquake south of Honshu, Japan. Standard array techniques (slantstacking), applied to broadband data from the global broadband network, the German Regional Seismic Network (GRSN) and the Gr¿fenberg (GRF) array, and synthetic seismogram modeling, reveal that these unusual phases are S to P conversions from under the seismic source. Timing of the converted phase indicates that subduction has had little, if any, effect on the depth of the '660 km' discontinuity. This study shows that upper mantle seismic structure can be constrained from single events using the presently available broadband seismic data and applying array techniques to network data. ¿ American Geophysical Union 1994