NOTE: This paper is in press at AGU Books and has USGS BAO approval for publication (IP-152990). The final version may contain copy edits.
Abstract
Seismic hazard models rely on earthquake recurrence estimates, but histories of earthquakes with long recurrence intervals can be difficult to derive for subduction zones from historical seismicity alone. Here we present an earthquake recurrence model for the subduction interface of the Alaska-Aleutian subduction zone based on geodetic and paleoseismic data. To capture variations in rupture behavior along strike, we define fault sections based on geodetic coupling, prehistoric earthquake and tsunami recurrence, historical ruptures, and geologic and geophysical structure. From east to west along the subduction zone, several key findings guide construction of the recurrence model. The Yakataga section exhibits a complex interplay of strain accumulation along the Yakutat plate interface and upper-plate faulting. In the 1964 Mw 9.2 rupture area, which spans four fault sections, recurrence rates for section participation in presumed great (Mw 8.5+) events vary from ~600 years (Prince William Sound section) to ~380 years (Kodiak section), geodetic character varies substantially along strike, and geologic evidence indicates rupture patches vary in space and time. Westward along the Semidi section, recurrence of large, tsunamigenic ruptures are far more frequent (~220 years) based on geologic and geodetic data than previously assumed. The seismic potential of the Shumagin section, an area of low coupling, remains enigmatic despite a large (Mw 7.8) rupture in 2020. The neighboring Sanak section, which is nearly freely slipping, appears to produce large events every ~1,000 years, most recently in 1946 (Mw 8.6). Prehistoric tsunami data indicate that large rupture recurrence in the Fox Islands is ~210 years. Paleoseismic data is lacking west of the Fox Islands, so rupture rates along the western 1900 km of the subduction interface to Komandorski rely on geodetic constraints. Simple recurrence estimates from geodetic data suggest that rates for Mw 8+ earthquakes are higher than previously assumed from seismicity alone west of the Fox Islands.