2.2 Subduction interface sections
We assign fault sections to broadly characterize earthquake recurrence
and slip deficit rates along strike of the AASZ (Figure 1). Our
selection of the term ’section’ rather than ’segment’ is intentional, as
our analysis is not meant to imply that each section is a fixed rupture
segment. Previous segmentation models of the AASZ focused primarily on
the historical pattern of ruptures, mainly inferred from aftershock
zones (Davies et al., 1981; McCann et al., 1979; Sykes, 1971) (Figure
2). Here we define fault sections in part by historical and prehistoric
rupture patches, but also geodetic data, geologic observations of
land-level changes and tsunami recurrence, and structural observations.
The sections are modified from those presented in the 2007 NSHM (Wesson
et al., 2007) and many closely follow those defined by a coordinated
effort by the National Tsunami Hazard Mitigation Program to devise
tsunami source models for Alaska (Ross et al., 2023). The sections vary
in length, ranging from from ~95 km (Barren Islands
section) to ~540 km (Komandorski section) (Figure 1).
We defined sections based on observed along strike changes in criteria:
changes in slip magnitude and/or depth range of slip in historical great
earthquakes, changes in the interseismic slip deficit distribution (rate
or spatial pattern) based on geodetic studies, or changes in earthquake
recurrence estimated from paleo-earthquake or paleo-tsunami studies. We
required along-strike changes in at least two of these quantities to
define a section boundary. For example, the Barren Islands section, the
shortest in our model, was defined (see Section 3 for details) based on
a significant narrowing of the region of slip deficit observed in
geodetic models (Suito & Freymueller, 2009; 2020), plus a corresponding
narrowing of the region of slip in 1964 in the model of Ichinose et al.
(2007).
The hazard modeling approach that will use our model values does not
allow for variations in slip deficit with depth, but only updip and
downdip limits of the seismogenic zone and a slip deficit rate/moment
accumulation rate. The downdip limit is estimated from slip in known
great earthquakes or from geodetic estimates. The updip limit is
difficult to estimate because geodetic studies have very limited model
resolution near the trench, and usually no more than one large or great
earthquake has a known slip distribution. Even where earthquake slip
distributions have been modeled, the extent of shallow slip may be
poorly constrained without near-trench observations (e.g., Brooks et
al., 2023). The tsunami record can demonstrate evidence of past slip to
the trench (or near it), but if we lack clear evidence for the slip
behavior of the megathrust at shallow depth, or if previous coupling
models lack clear updip limits, we assume that the updip limit of slip
deficit extends to the trench.