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Design Considerations for an Offshore Instrument Network for Tsunami Early Warning in the Cascadia Subduction Zone
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  • William Wilcock,
  • David Schmidt,
  • Randall LeVeque,
  • Frank Gonzalez,
  • Diego Melgar,
  • Brendan Crowell,
  • Paul Bodin,
  • Geoff Cram,
  • Michael Harrington,
  • Dana Manalang,
  • Emily Roland
William Wilcock
University of Washington

Corresponding Author:wilcock@uw.edu

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David Schmidt
University of Washington
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Randall LeVeque
University of Washington
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Frank Gonzalez
University of Washington Seattle Campus
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Diego Melgar
University of Oregon
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Brendan Crowell
University of Washington
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Paul Bodin
University of Washington
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Geoff Cram
University of Washington
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Michael Harrington
University of Washington
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Dana Manalang
University of Washington
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Emily Roland
University of Washington
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Abstract

We report on a feasibility study for an offshore instrument network in the Cascadia subduction zone to improve earthquake and tsunami early warning. The global DART buoy network provides effective warning for far-field tsunamis but near-field tsunami warning is challenging because the lead time is short and near-source observations are rarely available to directly measure the sea surface disturbance and evolution. Near-field tsunami warnings presently rely on rapid point source seismic inversions that do not estimate tsunami wave height. Efforts are underway to incorporate GNSS data into rapid source inversions that would support an initial near-field tsunami prediction. Offshore observations would contribute further to near-field tsunami warnings by providing: first, direct observations of seafloor and sea surface displacements during earthquake rupture and second, ongoing measurements for continued forecast refinement. Offshore instruments could also detect tsunamis triggered by submarine landslides and by so-called “tsunami” or “slow” or “silent” earthquakes that can generate unexpectedly large tsunamis but are characterized by shaking intensity so low as to be undetected or ignored. Pressure observations in the source zone will be challenging to interpret because they are dominated by seafloor accelerations and hydroacoustic waves rather than changes in hydrostatic pressure. In an effective system, pressure observations may need to be complemented by other observations such as inertial measurements of seafloor displacement, GNSS buoys and high-frequency coastal radar. It may also be important to place pressure sensors just seaward of the source zone to measure the developing tsunami in a region with an undisturbed seafloor. We will discuss alternative design options for an offshore instrument network in Cascadia, the research and development that must to be completed to determine the best approach, and the role of offshore observations in a holistic plan for tsunami mitigation.