Towards a Real-Time, Seafloor Based, Earthquake Early Warning System for the Pacific Northwest
DOEI Funded Project: 2007
Earthquake Early Warning (EEW) systems have become common on land in the last 5 years. These systems continually process real-time seismic data to determine when a potentially damaging earthquake is underway. They utilize the first arriving, low-amplitude P-waves to predict the impending arrival of the higher energy later arriving waves which actually cause damage. In Japan, dense instrument networks detect most earthquakes within 3-5 seconds after they start. Since building damage typically occurs 10-500 seconds after a rupture starts, computers have sufficient time to take precautions including shutting off gas lines and stopping trains. The most advanced algorithms can differentiate between a relatively minor M6 earthquake and a catastrophic M7-9 earthquake using only the first few seconds’ worth of data. Unfortunately, the largest earthquakes in the world, subduction zone mega-thrusts like 2004 Sumatra, occur offshore where real-time seismic data is usually unavailable. These earthquakes are great candidates for EEW because they typically start 50-150 km from the nearest (onshore) building, meaning there is an even greater lead-time to process data and issue warnings. Moreover, if this type of seafloor data were available, it would greatly improve our ability to differentiate between M9 earthquakes that generate damaging tsunamis and M8 earthquakes that generate only minor tsunamis. Installing an earthquake early warning system for the Magnitude 8-9 earthquakes that are expected offshore of Oregon and Washington would be one of the most societally relevant applications for seafloor observatory science. Unfortunately, both the ORION program and NOAA’s DART system purposely ignore this goal. As co-PIs on the subduction zone part of the ORION program’s Regional Cabled Observatory we have been very frustrated by this. However, we have recently received encouragement from the director of NOAA’s tsunami program, Dr. David Green, who is similarly frustrated with his own program’s inability to address the problem of warning the people in the most danger from tsunamis, namely those that live close to the epicenter. We will submit an NSF proposal in August to do a test-deployment of an EEW system that builds on the success of WHOI’s 1-year deployment of an acoustically-linked moored buoy observatory. Dr. Green has encouraged us to seek NOAA ship time to deploy an improved version of the Nootka Buoy off the Cascadia subduction zone for two years to demonstrate the feasibility of using Ocean Bottom Seismometers (OBSs) as part of a real-time warning system. To be ready for this proposal, we seek DOEI funding to add real-time onboard processing and decision-making capabilities to the current WHOI OBS design, and interface this capability with the WHOI acoustic modem. We view a demonstration of these improvements as vital for capturing NOAA’s current level of interest and using it to nucleate a major new ocean observatory project.