Constraints on the Alaska-Aleutian Subduction Zone from MCS and OBS Data of the ALEUT Project

The Alaska Langseth Experiment to Understand the megaThrust (ALEUT) program acquired deep penetration multichannel seismic (MCS) reflection and ocean bottom seismometer (OBS) data along a part of the Aleutian subduction zone that exhibits the full spectrum of coupling, from locked to freely slipping. The goal of this program was to characterize variations in the geometry and properties of the megathrust, over-riding and downgoing plates and other structures and relate them to downdip and along-strike changes in slip behavior and seismogenesis. The study area encompassed 1) the freely slipping Shumagin Gap; 2) the locked Semidi segment, which last ruptured in 1938, and 3) the locked western Kodiak asperity, the western extent of the 1964 M9.2 rupture. In this talk, I will summarize some of the major findings from this marine geophysical experiment. I will particularly focus on three points: - the link between oceanic plate fabric, hydration and subduction zone seismicity - the variations in reflection characteristics of the megathrust fault with depth and how theses variations may relate to changes in fault structure and seismic behavior - the seismic imaging of a major fault system in the over-riding plate within the Shumagin gap and how these large-scale structures are sufficiently profound to play a major role in the behavior of the megathrust in this area and segmentation of great earthquake rupture area.