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The origin of rupture segmentation along subduction zone megathrusts and linkages to the structural evolution of the subduction zone are poorly understood. Here, regional-scale seismic imaging of the Cascadia margin is used to characterize the megathrust spanning ~900 km from Vancouver Island to the California border, across the seismogenic zone to a few tens of kilometers from the coast. Discrete domains in lower plate geometry and sediment underthrusting are identified, not evident in prior regional plate models, which align with changes in lithology and structure of the upper plate and interpreted paleo-rupture patches. Strike-slip faults in the lower plate associated with oblique subduction mark boundaries between regions of distinct lower plate geometry. Their formation may be linked to changes in upper plate structure across long-lived upper plate faults. The Juan de Fuca plate is fragmenting within the seismogenic zone at Cascadia as the young plate bends beneath the heterogeneous upper plate resulting in structural domains that coincide with paleo-rupture segmentation. 

This data set was acquired with a Kongsberg Maritime EM122 Multibeam Sonar during R/V Marcus G. Langseth expedition MGL2104 conducted in 2021 (Chief Scientist: Dr. Suzanne Carbotte, Investigators: Dr. Jeffrey Beeson, Dr. Suzanne Carbotte). These data files are of MBSystem-compatible format (format 121, Generic Sonar Format) and include Acoustic Backscatter, Sidescan and Swath Bathymetry data that were processed after acquisition. This data was processed by OSU and is included in the Global Multi-Resolution Topography (GMRT) Synthesis (version 4.0). Data were acquired as part of the project(s): Collaborative Research: Illuminating the Cascadia plate boundary zone and accretionary wedge with a regional-scale ultra-long offset multi-channel seismic study. Funding was provided by NSF award: OCE18-27452.