Northern Cascadia: Extent of locked zone, prism deformation, slip-to-toe, and the edge of subduction
The aim of the SO294 – CLOCKS cruise is to investigate subduction earthquakes using the Cascadia continental margin off Vancouver Island as an example. Earthquakes at subduction zones with magnitudes M>8.5 are among the most hazardous earthquakes worldwide. The Cascadia subduction zone is one of the regions for which such an earthquake is expected in the near future. Despite decades of intensive research, many questions remain about the behaviour of the Cascadia seismogenic zone off Vancouver Island and important details about the tectonic structure along the deformation front have not yet been explored. The focus of SO294 is to determine the boundary of the seismogenic zone, especially the seaward limit. For this purpose, seismic data are used together with bathymetric data to map the deformation structure and fragmentation of the deformation front. Thermal data are combined with seismic methods to determine the temperature at the plate boundary and associated drainage processes. Magnetotelluric data along an approximately 230 km long amphibious profile will be acquired to determine the extent of this fault surface and fluid accumulations at the lower limit of the seismogenic zone. All of these data will help to determine whether the seismogenic zone has ruptured to the base of the accretionary wedge during previous earthquakes. This will not only make it possible to better isolate geohazards from such subduction earthquakes off Cascadia, but also improve estimates of the tsunami hazard. The work builds on an excellent collaboration with the Geological Survey of Canada, the University of Alberta, the Japan Agency of Marine-Earth Science & Technology (JAMSTEC), Kobe University, University of Tokyo, and Ocean Networks Canada (ONC).