The amplitude of coda from local shallow earthquakes in the southern Kanto district of Japan does not decay smoothly with time. A clear phase appears in the S coda at lapse time from 15 to 45 s measured from the S wave arrival, and it is predominant for frequencies around 8 Hz. This phase seems to be an S wave reflected from a discontinuity inclined westward at upper mantle depths since it is predominantly on the horizontal components and propagated westward with a high apparent velocity. Applying an inversion method to the travel times of the phases read from 8-Hz band seismograms, we locate the S wave reflector near the upper plane of the double seismic zone associated with the subducting Pacific plate. The S wave reflector is resolved east of the volcanic front at a depth of 80--100 km. If we put Qs-1=10-3, the reflection coefficient is estimated to be around 0.5; however, the scatter is large. The S wave impedance contrast at the interface seems to be very large. It may suggest the existence of a zone containing many liquid bodies. ¿ American Geophysical Union 1988