Seafloor Geodesy

Cascadia subduction zone is overdue for a major earthquake. A key question regarding natural hazards is whether such an earthquake can generate a large tsunami. Our ability to answer this question is limited by the lack of deformation measurements near the shallow portion of the subduction zone.

Recently, my group started to collaborate with physical oceanographers at GSO (Randy Watts and Kathleen Donohue) to investigate this problem. Funded by the National Science Foundation (award 1728060), we deployed four Current and Pressure Recording Inverted Echo Sounder (C-PIES) offshore Oregon in April 2017 to quantify the water-column contributions using in situ observations (Figure 1). C-PIES (Figure 2) are unique because they simultaneously measure bottom pressure, current, and round-trip acoustic travel time from the sea floor to surface and back. By combining these measurements, the water signal can be separated from the measured bottom pressure signal. We will recover these instruments in November 2017.

Figure 1. Map of the study site offshore Oregon. The magenta circles are proposed sites of the four CPIES. Three will be co-located with the UW benchmarks. The black lines are seafloor cable as part of the Ocean Observatory Initiative (OOI) project. Red nodes are the voltage nodes. The green squares are benchmarks for BPR and ASCPR measurements by the UW-SIO Cascadia project.
Figure 2. The CPIES is a bottom-mounted instrument that measures pressure at the sea floor, current speed and direction 50 meters above the bottom, and acoustic travel time from the sea floor to the sea surface and back. Instrumentation is self-contained with an acoustic release and flotation buoyancy. Instrument enhancements include a pop-up data shuttle where disposable capsules rise to the sea surface and send data to shore via satellite links, and an acoustic Doppler current profiler directly attached to the inverted echo sounder.