3.3 Kenai section
The Kenai section (Figure 3) extends approximately 125 km between Seward
and Homer and lies between regions of major slip along the Prince
William Sound and Kodiak sections in 1964. Pulpan & Frohlich (1985)
suggested that the Kenai and adjacent Barren Islands sections (roughly
their ‘Central Segment’) may exhibit different rupture behavior than the
Prince William Sound and Kodiak sections due to tears in the downgoing
slab. Hutchinson & Crowell (2007) examined regional archeological and
paleoseismic ages and deduced that the Kenai section ruptures together
with the adjacent PWS section but independently of the Kodiak section.
Tape and Lomax (2022) show that the Kenai and neighboring Barren Islands
section correspond to a local minimum in the spatial distribution of
aftershocks of the 1964 rupture.
Paleoseismic data indicate that the Kenai section exhibits different
rupture behavior than the neighboring Prince William Sound section. Mann
& Crowell (1996) first documented a rupture at Verdant Cove
~800 BP, and Kelsey et al. (2015) interpret this event
as the 1060-1110 CE rupture identified by Shennan et al. (2014), which
was initially interpreted as a multi-section rupture equal to or larger
than the 1964 earthquake, but may have been a rupture centered only on
Kodiak (Shennan et al., 2018). Kelsey et al. (2015) also identified
evidence for an additional, younger earthquake at 1530-1840 CE. Several
rupture scenarios fit the younger 1530-1840 CE data, including rupture
with the adjacent Kodiak section, rupture in the historical 1788 event,
or independent rupture of the Kenai section. Shennan et al. (2016)
report peat-mud couplets at their Kasilof and Homer sites that may
correspond to older subduction ruptures (e.g., ~2050
BP), although more study would be useful to develop the earthquake
chronology at these sites. We limit our analysis to the chronology of
Kelsey et al. (2015), which provides a closed-interval mean recurrence
of ~441 years (Table 1).
Geodetic observations along the Kenai section show that the interface is
highly coupled but that the width of coupling is much less than the
neighboring Prince William Sound section and confined to mostly near the
trench (Freymueller et al., 2000; Li et al., 2016; Suito & Freymueller,
2009). Here we model a 100% coupled seismogenic zone extending
~225 km from the trench with a downdip depth of
~20 km (Li et al., 2016) (Figure 3).