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.