We address the use of regional broad-band waveform data to better constrain the upper mantle transition zone structure. We then show evidence of high velocity anomalies in the transition zone associated with the southern Kurile subduction zone. Modeling of the triplicated regional waveforms supports that high velocity anomalies exist in the deeper part of the transition zone (over 500 km in depth), and the ''660'' discontinuity may be depressed to about 690 km depth. Our results suggest there is some degree of flattening of the slab in the southern Kuriles. ¿ American Geophysical Union 1995