Relation between the subducting plate and seismicity associated with the great 1964 Alaska earthquake

Tectonic studies of the great 1964 Alaska earthquake have underappreciated the nature of the subducted plate in influencing seismicity. We compare sei smological observations in the Prince William and Kodiak areas that rupture d during this earthquake with the corresponding morphology and structure of the subducting plate. The upper plate geology (Prince William Terrane) and velocity structure are the same in both areas. In the Prince William area where the Yakutat Terrane subducted, the energy released and coupling were stronger than above the Kodiak subduction zone where thick trench sediment subducts. The conjecture that lower plate character or the amount of subduc ted sediment affects coupling helps explain variability in seismology, geod etic inversions and the horizontal velocity of GPS stations.