2.1 Subduction interface geometry
Prior studies in Alaska have used a wide range of interface geometry
models. The subduction interface geometry we use is simplified as a
planar fit to the Slab2 interface model (Hayes et al., 2018) for use in
hazard calculations. Generalization of the interface is reasonable
because (1) at the shallow levels of the seismogenic interface where
curvature is minimal, a plane is a reasonable approximation of the
interface geometry; (2) the geodetic coupling models we use to calculate
slip deficit rates assumed planar surfaces; and (3) geodetic polygons
are not used to model seafloor deformation to generate tsunamis or
predict the downdip extent of slip, but instead are used as a way to
approximate moment accumulation.
The criteria above led us to approximate the potentially seismogenic
plate interface as a series of rectangular elements, one for each
section. The downdip width of the inferred seismogenic zone, combined
with a slip deficit rate that is based on the relative plate motion
multiplied by a coupling coefficient, gives a reasonable first-order
approximation for the moment accumulation rate. As moment accumulation
rate is the primary focus, we do not attempt to model spatial complexity
at a smaller scale, but instead will average the slip deficit
rate/coupling coefficient over the rectangle.