SEATTLE — Washington’s coastal communities face a significant threat from tsunamis, with potential water heights reaching three stories in some areas following an offshore magnitude 9.0 earthquake.
Adding to the threat, a major earthquake generated by the nearby Cascadia subduction zone could trigger one such tsunami that would arrive as quickly as 15-30 minutes.
To address this risk, researchers are developing ways to get tsunami warnings out faster to residents at NOAA’s Pacific Marine Environmental Laboratory in Seattle’s Sand Point neighborhood. Now in their fourth generation, a fleet of 50 or so Deep-ocean Assessment and Reporting of Tsunamis (DART) buoys, strategically placed worldwide, can detect and measure tsunami waves.
The buoys are strategically placed, transmitting a signal detected from a sensor 6,000 meters underwater. Those sensors can detect a wave fluctuation of less than 1 cm.
The dart buoys are heavily engineered. The cables that anchor them are resistant to shark bites, and the spool the cables unwind from is designed to unravel delicately upon deployment so they don’t become entangled. And the latest upgrade: The buoys can now differentiate between seismic waves and tsunami waves. This is key, as the buoys have the opportunity to be relocated closer to the triggering source – the Cascadia subduction zone. That means the tsunami wave will arrive at the buoy faster, so analyses and alerts can come faster as well.
“That allows us to detect the tsunami in the order of 10-15 minutes earlier than the previous generation,” explained Diego Arcas, a research scientist with NOAA’s Center for Tsunami Research.
That extra lead time would be critical for a tsunami potentially arriving on the Washington coast in as little as 15-30 minutes.
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While it may be a once-in-a-lifetime event, or once in several lifetimes, it has happened before. Over and over.
Coastal hazards specialist Carrie Garrison-Laney has seen it, right under her nose, literally. For 25 years, she has been digging into tidal marshes, uncovering a literal record of past tsunami activity. Bringing with it, turbulent flow, washing sand ashore and into normally quiet tidal marshes.
One site in particular that has more tsunami deposits than anywhere else in Washington is Discovery Bay.
Protected from the most frequent storm waves, Discovery Bay’s tapered shape serves as a funnel that directs tsunami wave energy toward its tapered terminus, accepting sand washed ashore from the turbulent flow of the occasional tsunami.
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Between each layer of “tsunami sand” is a hundred or so more years of marsh peat, which are organics that can be dated with radiocarbon.
“As you go down in section here, you’re going back in time,” Garrison-Laney explained as she showed a long core of soil, pointing out the most recent tsunami generated by a Cascadia subduction zone earthquake, “This one is from 1700.”
The tsunami record buried in the dirt goes back thousands of years. It provides clues as to how often these megaearthquakes occur.
From mud to modeling, Arcas has been building upgrades to high-resolution wave models that can pinpoint specific neighborhoods and risk levels of tsunamis.
“We can compute really fast and get an estimate of the inundation, wave elevation, duration of the event, number of waves, pretty accurate forecast in a matter of a couple of minutes,” he explained.
Arcas is also assessing the “time dependency” impact on a tsunami, the idea that an earthquake doesn’t happen instantaneously at one point, rather it can rupture over 5 minutes, propagating along the entire fault zone, maybe 1,000 miles in the case of the Cascadia subduction zone – which can impact the tsunami wave generated and impacts.
Moving forward, the team at PMEL is currently working to upgrade older buoys to the new fourth-generation model.
Relocating current buoys closer to the earthquake source is a detailed process, involving additional studies on ocean currents and survivability of the buoys – and electronically engaging the 4G capabilities.
As it stands now, the best precaution for someone along Washington’s Pacific coast living in a tsunami zone is to head to higher ground once a strong earthquake is felt.
Meanwhile, scientists will continue to develop these systems to make tsunami warnings quicker and more accurate.
