Presentation Information
[U15-P06]Advancing Offshore Earthquake and Tsunami Early Warning in Cascadia
*William S D Wilcock1, Zoe Krauss2, J Renate Hartog2, Mikael Mazur3, Nicolas K Fontaine3, Roland Ryf3, David T Neilson3, David A Schmidt2, Bradley P Lipovsky2, Marine A Denolle2, Harold J Tobin2, Paul Bodin2, Mika Thompson2, William J Dienstfrey2, Alexander Rose2, Dana A Manalang4, Yoichiro Dobashi1, Michael J Harrington4 (1.School of Oceanography, University of Washington, Seattle, 2.Department of Earth and Space Sciences, University of Washington, Seattle, 3.Nokia Bell Labs, New Providence, New Jersey, 4.Applied Physics Laboratory, University of Washington, Seattle)
Keywords:
Cascadia Subduction Zone,offshore early warning,submarine telecommunication cables,seafloor cabled observatory
The Cascadia subduction zone fault off the coast of Northern California, Oregon, and Washington, USA, and British Columbia, Canada, is known to produce great earthquakes and resulting tsunamis comparable to the devastating 2004 Sumatra magnitude 9.2 and 2011 Japan magnitude 9.0 earthquake disasters. For this reason, the geoscience research and disaster risk management communities are working to address scientific questions regarding these events and incorporate new knowledge into efforts to mitigate the hazard and improve societal resilience. An important component of hazard mitigation is enhancements to earthquake early warning and tsunami forecasts. Submarine observations are important for these objectives because the seismogenic zone of the Cascadia megathrust lies offshore. In Japan, there are extensive networks of offshore cabled infrastructure to support timely and accurate warnings for offshore earthquakes as well as scientific research to improve the hazard assessment. In Cascadia, dedicated scientific infrastructure is limited to the Ocean Networks Canada (ONC) NEPTUNE cabled observatory off Vancouver Island and the Ocean Observatories Initiative’s Regional Cabled Array (OOI RCA) off central Oregon. Offshore observations from the ONC cabled observatory presently support earthquake early warning and tsunami forecasts. However, the OOI RCA does not, and implementing early warning on the OOI RCA would account for only a small portion of the subduction zone. A dedicated cabled system for early warning spanning the entire US subduction zone would be very expensive, and there is little prospect of funding such a system in the short to medium term. An alternative approach would be to take advantage of the numerous telecommunication cables that land in the Pacific Northwest by repurposing retiring cables for early warning, adding multiplexed fiber sensing to operational cables, and incorporating conventional geophysical sensors (SMART Cables) and enhanced fiber sensing into new telecommunication systems. Early warning infrastructure could also be incorporated into wind farms if they are installed in the region. If real-time DAS data could be collected from the current configuration of submarine telecommunication cables and were incorporated into the existing U.S. ShakeAlert earthquake early warning system, more than 50% of the submarine forearc region could benefit from an additional 10-18 s of improved earthquake detection time. A private-public partnership for early warning will be challenging to implement, but the first step is to demonstrate the feasibility of the approach. The OOI RCA can contribute to this objective by testing new technologies and prototyping early warning systems. The US National Science Foundation is funding the Cascadia Offshore Subduction Zone Observatory (COSZO) project to enhance the OOI RCA to support geophysical studies. The seismometers and pressure gauges installed can contribute to early warning, and the system could be expanded by prototyping SMART sensor systems suitable for telecommunications cables. The OOI RCA has also supported three short open-access experiments of distributed acoustic sensing (DAS) on its two cables. The first occurred during an observatory shutdown, while the second demonstrated the feasibility of permanent multiplexed DAS out to the first repeaters during observatory operations. This past winter, the OOI hosted a 3-month experiment that combined multiplexed DAS with the multi-span DAS system developed by Nokia Bell Labs that leverages the high-loss loopback couplers within repeaters to extend observations further offshore. The data from this experiment are presently being prepared for public release, but the multi-span system successfully recorded M4.1 and M6.0 earthquakes on the Blanco Transform spanning the subduction zone illustrating its potential for earthquake early warning. Conventional sensors on the OOI RCA will help calibrate the multi-span observations.