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.