DO ALONG-STRIKE CHANGES IN SUBDUCTION PLATE GEOMETRY INFLUENCE INTRACONTINENTAL STRESS LOCALIZATION? NUMERICAL MODELS OF THE PACIFIC-YAKUTAT-CENTRAL ALASKA PLATE BOUNDARY

The complex geometry of Alaska's south-central subduction interface and the boundary element method are used to investigate whether changes in strike direction and/or changes in the along-strike dip of the subduction interface influence stress localization 200 to 500 km from the trench. We partition the Pacific-Yakutat-central Alaska subduction zone into three segments: Kodiak (strike 58°), Prince William Sound (PWS) (strike 87°), and Trans (strike 58-33°). All of the segments ruptured during the 1964 great Alaska earthquake (Mw 9.2). The Kodiak segment, southwest of longitude -153.2° is characterized by classic subduction of the Pacific Plate at an angle of <10° for 150 to 175 km before it rapidly steepens. The PWS segment, east of longitude -142.3°, subducts at an angle of 5 to 9° for an anomalous 350 to 450 km before it steepens. The Trans segment, located between the Kodiak and PWS segments, is characterized by rapid to gentle changes in the spacing and strike of Waditi-Benioff zone contours, northward dying out of the volcanic arc, and along strike variations in the percent of trench-perpendicular motion of the subducting plate. Active, fault-cored anticlines within Cook Inlet Basin lie >200 km inland from the Trans segment trench and appear to correlate with along-strike changes in subduction zone geometry. Changes in Navier-Coulomb stress on upper Cook Inlet faults support this correlation as modeled using geometrically-accurate boundary element method models of large magnitude subduction zone earthquakes. The results have significant implications concerning the mechanical stability and seismic potential of faults within Cook Inlet Basin.