RETRODICTING CASCADIA SUBDUCTION ZONE GREAT EARTHQUAKE SOURCE CHARACTERISTICS FROM TSUNAMI INUNDATION ALONG THE OREGON COAST

Inundation of low-lying coastal regions by tsunami following a Cascadia subduction zone earthquake is one of the most pressing, acute natural hazards facing coastal communities in the Pacific Northwest. More than two decades of research now underlies a near consensus that a future large earthquake along the Cascadia subduction zone is inevitable. Significant uncertainty remains, however, regarding the magnitude of displacement in such an event as well as the spatial extent of rupture along the fault zone; both are key factors that directly influence earthquake magnitude, tsunami generation, and coastal impacts. Existing models of tsunami inundation, in particular, demonstrate the close linkage between rupture scenario and site-specific inundation at the scale of individual estuaries. Our team is in the initial phase of developing a project exploring rupture scenarios by looking seaward from selected estuaries along the coast. Looking seaward involves two components. First, we seek to characterize tsunami deposit thickness, sedimentology, and distribution in estuaries with a clear record of tsunami deposition to build hydrodynamic models for exploration of the range of flow conditions capable of delivering and distributing sediment into an estuary. Hydrodynamic models will be coupled to a fault-coupling model in an effort to test existing Cascadia subduction zone rupture scenarios. The second component centers on developing the scientific framework in consultation with coastal emergency managers, land use planners, and communities. This dimension of the study is an attempt to incorporate end-user input into the study design. Understanding how communities use data and existing tsunami hazard maps is a key step needed to develop next-generation tsunami inundation models and to increase coastal community resilience.