Using multiple ScS reverberations, we examine the mantle reflectivity structure beneath northeast China and the northwest Pacific. We find several upper mantle discontinuities, including a melt layer with a mean thickness of 64 km atop the 410 km discontinuity, present on both sides of the subducting slab near the Nankai trench. The transition zone contains a split 520 km discontinuity in several paths, and tomographic images show stagnant slabs at this depth. We believe that this may be slab related based on experimental work. A negative reflector is found in one path beneath the northeast China craton at a depth of 598 km. Mid-mantle reflectors are found in all of our paths and are present throughout a wide depth range (~750–1600 km).