3.14 Komandorski section
The Komandorski section (Figure 6) extends ~530 km from
near the western edge of Attu to the western end of the AASZ. Although
this section is not included in the USGS NSHM, we include it here for
completeness. There is no historical subduction interface rupture larger
than Mw 6 or deeper than 50 km recorded along this
section of the subduction zone (Kogan et al., 2017), nor is there active
volcanism (Newberry et al., 1986). The 2017 Mw 7.8
earthquake near Komandorskiye Ostrova (also known as Komandorski
Islands) in Russia ruptured nearly 400 km of the strike-slip Bering
fracture zone between the Komandorski sliver and the Bering plate (Lay
et al., 2017).
A substantial component of relative Pacific-Bering plate convergence is
arc-parallel in the Komandorski section. Modeled geodetic observations
indicate that lateral motion is accommodated along primarily along
backarc strike-slip faulting as demonstrated in the 2017
Mw 7.8 rupture, but also as oblique convergence along
the shallow subduction interface (Kogan et al., 2017; Lay et al., 2017).
It is unclear if shallow interface slip is completely strike-slip as
depicted in Lay et al. (2017), or if it is oblique or even occasionally
trench-normal on the interface. Given the occurrence of subduction
interface slip near the Andaman Islands (India) in the
Mw 9.15 Sumatra–Andaman earthquake of 2004 where the
Indian Plate converges obliquely under the Andaman Islands (Chlieh et
al., 2007), we do not discard the idea that highly oblique relative
plate convergence can lead to interface slip.
Geodetic observations in the Komandorski section can be fit with a model
of a rigid Komandorski sliver moving westward at ~51
mm/year, bounded by the Aleutian subduction interface to the south and
by the Bering fracture zone to the north (Kogan et al., 2017). Our
calculation of relative Pacific - arc velocities (Table 2) indicates
that as much as 38 mm/yr of convergence is available for interface slip.
In the context of these models, we infer 100% coupling on the shallow
subduction interface from the deformation front to a map distance of
~55 km arcward, corresponding to a depth of
~15 km (Figure 6).