Multichannel seismic reflection data collected near the southern Kenai Peninsula, Alaska, show deep events that could stem either from a linear diffractor or from a curved reflector. Whichever is the cause, it must be at a minimum depth of 12 km. If a linear diffractor causes the most obvious events, it strikes at a 60¿ angle across the surface trend of Mesozoic rocks. Thus the diffractor could be associated with a transverse tectonic boundary that, on the basis of other evidence, is thought to strike through the area of this study. Alternatively, these deep events could be reflections from rocks associated either with a detached piece of oceanic crust or with the downgoing Pacific plate. Theses associated rocks could be porous and overpressured sedimentary rocks that are squeezed between indurated or metamorphosed sedimentary rocks in the overthrust plate and igneous rocks in the downgoing oceanic crust.