Late Holocene spatial patterns of coseismic land level changes and earthquake rupture areas, south-central Alaska

Previous investigations of multiple late Holocene earthquake events in Cook Inlet suggest different spatial patterns of co-seismic subsidence for the 1964, ~900 BP and ~1500 BP great earthquakes . One hypothesis to explain these differences is that they record variations in the location, extent or depth of the rupture zone. Testing this hypothesis is important if we are to reduce uncertainties regarding the nature of future earthquake hazard in south central Alaska and improve our understanding of the nature of past earthquake ruptures in this region. Here we study sites beyond Cook Inlet to address the issue of spatial variability; Copper River Delta and Cape Suckling record coseismic uplift, Middle Bay and Anton Larson Bay, Kodiak Island, record coseismic subsidence. The 1964 rupture involved two segments (Kodiak and Prince William Sound) of the Aleutian Megathrust. We aim to quantify coseismic deformation for three Late Holocene earthquakes: ~500BP, a single segment rupture of the Kodiak segment; and ~900 and ~1500BP earthquakes that we consider involved simultaneous rupturing of three segments. These are the Kodiak and Prince William Sound segments and the adjacent segment extending to the Pamplona - Malaspina thrust front in the east. In this scenario, the Yakataga seismic gap ruptures in conjunction with the Aleutian megathrust.