MASKING SUBDUCTION ZONE RHEOLOGY WITH SUBDUCTION ZONE GEOMETRY

One goal of studying earthquake cycle processes at subduction zones is to understand the physical conditions and characteristics that govern megathrust seismogenesis. Seismic, geodetic, geologic, and experimental studies suggest that velocity weakening material is characteristic of the portions of the subduction interface capable of generating earthquakes, while aseismic zones slide stably and are velocity strengthening. However, the geometry of the subduction interface itself may play a role in controlling the spatial distribution of interseismic coupling and coseismic slip. Using the USGS Slab1.0 geometries for the Chile-Peru, Cascadia, Aleutian, Kamchatka, Japan, Nankai, and Sumatra subduction zones, I investigate this hypothesis by calculating the traction induced on the seismogenic portion of the interface by interseismic creep on the deep interface down to 100 km, which in many regions is more geometrically complex than the shallow slab, as well as the coseismic slip that would be required to relieve this imposed traction. The spatial distributions of the stress and slip induced solely by subducting the corrugated slab show along-strike variations with wavelengths similar to great earthquake rupture areas and geodetically constrained estimates of interseismic coupling. This suggests that inferences of megathrust rheology based on parametrization of the seismogenic interface alone may actually reflect the combined effects of rheology and subduction interface geometry.