FOCUSING THE LENS OFFSHORE CASCADIA – RECENT AND EMERGING EFFORTS TO EXPLORE PLATE BOUNDARY BEHAVIOR AND UNDERSTAND OFFSHORE HAZARDS (Invited Presentation)

Improved observational capabilities and the occurrence of several great earthquakes in the past decade+ have lead to a clearer picture of the process of stress accumulation and the range of slip behavior associated with the inter- and coseismic cycle at subduction zones. Through this ‘focusing of the lens’ of subduction zone research, it is becoming apparent that answering the most pressing questions related to seismogenesis will require taking a detailed look at phenomena that occur offshore, closer to the source of large subduction zone earthquakes. In Cascadia, the effort to extend observations and models seaward of the coast has been aided by several community efforts, including the deployment of the Cascadia Initiative (CI) ocean bottom seismometer (OBS) array, the installation of the Ocean Observatory Initiative Regional Nodes and Ocean Networks Canada NEPTUNE cabled observatory, and several recent imaging experiments. Here, we will present an overview of a subset of ongoing efforts currently underway in Cascadia to refine our understanding of seismicity, deformation, and plate boundary structure in the offshore regime. These include investigations of margin-scale seismicity patterns and structure using OBS recordings from the CI, and an effort to develop seafloor pressure measurements as a tool for offshore geodetic monitoring. Related to these studies, knowledge of the structure of the accretionary prism and along-strike heterogeneity in sediment and faulting patterns will be critical for interpreting observations and anticipating the location of splay faults and strong asperities during future ruptures. New marine active source imaging data has helped to constrain these features in certain locations, but more modern data are necessary to extend this along strike. We will also discuss an emerging effort to explore the feasibility and design of a permanent system for offshore geophysical monitoring of the Cascadia subduction zone that will facilitate earthquake and tsunami early warning as well as long-term scientific research. Challenges and successes from the body of research currently being conducted offshore Cascadia should be used to refine hazard models and mitigation plans for a large Cascadia subduction zone earthquake, and guide the next generation of subduction zone observatories.