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).