SONNE SO294

Great megathrust earthquakes (M>8.5) at subduction zones and their tsunamis are among the most damaging natural hazards. At Cascadia, a megathrust earthquake is expected to occur in the foreseeable future. Little is known on whether and how the seismogenic behavior of the megathrust changes along the Cascadia margin. The detailed structure of the accretionary prism, segmented deformation front, style of faulting and vergence of thrusts, as well as the up- and down-dip extent of the locked zone remain uncertain. Especially north of the Nootka Fault Zone, little is known about the presence and extent of a subducted slab and the megathrust potential of the Explorer Plate system. We propose to acquire seismic data to image the frontal prism of the Juan de Fuca and Explorer Plates to seek structural signatures of slip-to-toe in past earthquakes, as e.g. recognized during the 2011 Tohoku event. Heat-flow data combined with seismic imaging will help to constrain the temperature regime across the deformation front to define the up-dip limit of the locked zone. A magnetotelluric experiment will address the down-dip end of the locked zone. Work is leveraged through collaboration with the Geological Survey of Canada, Japan Agency of Marine-Earth Science & Technology, and Ocean Networks Canada.