STRENGTH AND RHEOLOGY OF THE SUBDUCTION MEGATHRUST AND IMPLICATIONS FOR MODE OF SLIP (Invited Presentation)

Strength profiles of continental and oceanic lithosphere combined with models of fault stability provide first order predictions for the dominant deformation mechanisms at depth and the base of the seismogenic zone. These predictions are generally well-supported by structural studies of exhumed rocks and modern seismicity. However, despite the utility of this approach, similar strength and stability models for the subduction megathrust are difficult to implement. This is because of the lithologic complexity along the subduction megathrust, the unconstrained role of fluids along the megathrust, and differences in sediment input, thermal gradient, and geophysical observations of seismicity and modes of slow slip between each subduction zone. Here, we summarize what is known about the constitutive relations of the most abundant lithologies along the plate boundary and cite evidence from field based structural observations. We create strength profiles for 6 modern subduction megathrusts considering differences in thermal gradient, sediment inputs, and pore fluid pressure variability, and compare them to depths of seismicity, slow slip, and tremor. Although we find the predictions to be generally consistent with the geophysical observations, we discuss the unknowns that need to be resolved to make further progress.