REFLECTED AND MODE-CONVERTED SEISMIC-WAVES WITHIN THE SHALLOW ALEUTIAN SUBDUCTION ZONE, SOUTHERN KENAI PENINSULA, ALASKA

Pronounced secondary phases observed in local recordings of quarry shots and earthquakes on the southern Kenai Peninsula are identified as reflected P and S and converted S-to-P phases originating within four depth ranges: in the upper few kilometers of the Cook Inlet Tertiary basin, at midcrustal depths within the overthrust North American plate, at about 35 km depth near the top of the Wadati-Benioff seismic zone in proximity to the inferred interplate megathrust, and at about 5-10 km below the megathrust in the subducted Pacific plate. The positions and origins of the mid-upper plate (MUP) discontinuity and similar reflectors are discussed. It appears the the MUP discontinuity is seismically inactive and does not represent a brittle-ductile transition zone within the upper plate. The two converted S-to-P phases generated near the top of the subducted plate could indicate a low velocity zone associated with subducted oceanic crust. -after Authors