Complementing the 2020 Langseth offshore Cascadia survey with a large-N onshore nodal deployment

This deployment is an ambitious supplement to the Langseth offshore Cascadia survey scheduled for the summer of 2020. The focus of the onshore nodal deployment will be extending the ~20 2-D trench perpendicular offshore seismic lines ~50 km inland along the entire margin. Emerging work in subduction zones shows the controlled offshore source is well recorded on onshore receivers. Thus, we intend to leverage the scheduled Langseth survey to image the complete trench to wedge structure of multiple segments along the margin. A few, perhaps three or four 2-D lines will be extended further into the arc setting to investigate the along-strike variability observed in Cascadia using passive source techniques. Additionally, several smaller 3-D arrays will be attached to the 2-D lines that focus on locating tremor and investigating the fully 3-D geometry of the forearc. Instrument numbers available from the PIC supplemented with instruments from individual institutions are finally approaching the numbers where truly large-N style deployments are possible. The PIs included in this instrument request have extensive experience working in the area and with large nodal deployments. The timing of the offshore survey along with an increased availability of nodal instruments makes this deployment a potentially transformative data set in regard to our understanding of subduction related dynamics and hazards.