VARIATIONS IN SUBDUCTION BENDING-RELATED NORMAL FAULTING OF THE INCOMING JUAN DE FUCA PLATE ALONG THE CASCADIA MARGIN

Abstract

Cascadia Subduction Zone (SZ) is a natural laboratory for investigating bend-related normal faulting. Multichannel seismic data acquired along the incoming oceanic Juan de Fuca (JdF) plate dating back to the 1980s show along-strike variations in faulting patterns; however, the available data quality and coverage are limited. To characterize the along-strike bending fault variations of the JdF plate system, we interpret pre-stack depth migrated reflection images from the 2021 CASIE21 survey covering much of the Cascadia SZ. We identify nine distinct categories of reflection events, seven of which are interpreted to be related to extensional faults. Using fault density as an indicator of incoming JdF plate hydration, the study area can be subdivided into four offshore regions: Vancouver Island (~48°–50°N, average hydration), northern Washington (~47°–48°N, below average hydration), southern Washington and central/northern Oregon (~43.5°–47°N, most hydrated), and southern Oregon (~42°–43.5°N, least hydrated).