Figure 1. Study area along the Alaska-Aleutian subduction zone
(AASZ) showing the locations of fault sections and approximate
historical rupture areas. For older events, rupture areas are inferred
from aftershock zones (Tape and Lomax, 2022), and recent events are
taken from fault rupture models (Freymueller et al., 2021; Tape &
Lomax, 2022; Ye et al., 2022). Slab interface contours are from Hayes et
al., 2018. Bathymetry and shaded relief from GEBCO Compilation Group
(2023).
The last update to the Alaska portion of the U. S. Geological Survey
(USGS) National Seismic Hazard Model (NSHM) in 2007 used the best
available information to define recurrence rates for seven fault
sections along the subduction interface, primarily based on rupture
areas of historical subduction earthquakes (Wesson et al., 2007).
Maximum magnitudes were assigned to each fault section, and seismicity
and limited paleoseismic data were used to estimate rupture recurrence
(Wesson et al., 2007). At the time of the Wesson et al. (2007) update,
paleoseismic and paleotsunami records extended westward only as far as
Kodiak Island, and so seismicity rates exclusively were used west of
Kodiak to approximate the recurrence of large ruptures. Geodetic data
(Freymueller et al., 2008) were not incorporated in the 2007 update.
There have been several advances in the treatment of subduction zone
hazard since the last update of the Alaska portion of the NSHM in 2007.
In New Zealand, geodetic data were incorporated into the Hikurangi
subduction interface model of Stirling et al. (2012), where rupture
segments were defined based on the pattern of interseismic coupling,
slow slip events, and historical seismicity and earthquake recurrence
rates were inferred from plate convergence rates and coupling
coefficients. The most recent New Zealand seismic hazard model also uses
geodetic data, and leverages geologic data as a comparison, but not as a
constraint, in the inversion for rupture rates (Coffey et al., 2022). By
contrast, in Cascadia geodetic data are not used explicitly in
recurrence models, but instead a rich onshore and offshore paleoseismic
record is available to assign entire-zone and partial-rupture recurrence
rates (Frankel et al., 2015). Recent global subduction zone recurrence
models (Pagani et al., 2021) rely primarily on seismicity, especially
where paleoseismic data are lacking.
Here, we construct a recurrence model for the Aleutian-Alaskan
subduction zone using both geologic and geodetic data because these
datasets provide different, but complementary, views of rupture
behavior. Along the energetic coasts of Alaska, geologic data capture
only the largest ruptures, generally with preserved evidence of vertical
deformation above detection limits of > 0.2 m (Hawkes et
al., 2010; Shennan et al., 2016) or tsunami runup > 5 m
above the modern tidal range (Nelson et al., 2015; Witter et al., 2016,
2019) The geologic data also represent events that typically rupture
multiple fault sections, which is demonstrated by historical events and
inferred for prehistoric earthquakes. The geodetic data is used to
approximate strain accumulation and release by a single fault section.
Thus, recurrence rates of ruptures inferred from geodetic data are
necessarily shorter and the inferred earthquake magnitudes are smaller
than events recorded by geology. Our goal is to provide parameters
useful for seismic hazard analyses, such as for the next update of the
USGS NSHM. The model focuses on subduction interface ruptures rather
than outer rise, crustal, or intraslab events.