An earthquake rattled the Cascadia fault 325 years ago. Here's what we know about the massive quake
PORTLAND, Ore. (KOIN) – January 26 marked the 325th anniversary since the last earthquake struck the Cascadia Subduction Zone. Centuries later, the ancient quake has left clues for scientists to prepare for the next one.
The massive magnitude 9 quake stretched from Northern California to British Columbia, and sent a tsunami to Japan, researchers have found.
“The last Cascadia earthquake and tsunami occurred on January 26 in the year 1700 and it reached the shores of Oregon at approximately 9 p.m. The reason we can constrain it so tightly to that time of day even is in part because of Japan, who had very detailed records at that time of what they were experiencing on their coastline,” Laura Gabel, a geologist with the Oregon Department of Geology and Mineral Industries told KOIN 6 News Monday. “Also, Native American lore talked about the tsunami, the large shaking event and then water coming onshore.”
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The ancient quake also left behind geologic clues, including ghost forests in the Pacific Northwest.
“That’s actually one of the more beautiful geologic stories that we have in science. Folks that are from the coasts know that there’s these things called ‘ghost forests,’ tree trunks that are left standing that are no longer alive, sometimes they’re petrified. And they are a direct product of the earthquake in 1700. During the big events, the coast drops, sometimes by as much as four, five, six, seven, eight feet and then the trees end up being submerged into the salty water at these coastal marshes,” Diego Melgar, director of University of Oregon’s Cascadia Region Earthquake Science Center, previously told KOIN 6 News.
With Cascadia earthquakes expected roughly every 300-500 years, researchers are using those clues to prepare for the next tremor.
“We as a collective – not just my agency, but geoscientists as a whole – we do not have the capacity to predict when earthquakes are going to occur," Gabel noted. "Generally speaking, there is a lot of work being done at all levels of government and private institutions around the world to predict and to be able to have as much warning [for the next quake] as possible."
The geologist explained that Japan and California have advanced earthquake warning systems with seismometers tracking earthquake activity, noting there is some difficulty with warning systems for the Cascadia zone.
“The Cascadia Subduction Zone is tens of miles offshore in the deep ocean. So, listening for activity off there is much more difficult. There are seismometers on the ocean floor, and they are doing just that, but there are not many. And so, the scale of earthquakes that we're trying to listen for are just monumentally larger than anything else,” Gabel said.
While there is uncertainty of when exactly the next Cascadia quake could occur, Gabel said DOGAMI is working on a probabilistic assessment report for the state to provide guidance for building and bridge designs to ensure Oregon's infrastructure has a better chance of withstanding the next major quake.
Meanwhile, Gabel also reminds individuals to prepare.
“People can prepare [for a Cascadia Subduction Zone] earthquake, but the most important thing is just to know that it is a risk for us living here. It is a hazard, but it is survivable,” Gabel said.
“It’s just a matter of taking some time, if you’re going to the coast, to think about whether you’re going to be in a low-lying area that’s inside the tsunami zone, and if it is inside the tsunami zone, to just spend a moment thinking about what you route out of that area will be,” Gabel explained.
“We're trying to make it so that anyone that's coming to the coast is being made aware of this -- whether it's through their hotel or signage they're just seeing when you drive on [Highway] 101 you see you're entering and leaving tsunami [zone] signs, and that's all meant not just to show you where you are literally entering and leaving tsunami zone, but to get you thinking about it,” Gabel explained. “We made evacuation maps for every community on the coast, and we have an online viewer and smartphone app that will provide information on where location is with respect to the tsunami zone.”
Gabel also highlighted longer-term preparations for Oregonians to be prepared, including the Oregon Office of Emergency Management's guide to help Oregonians pack enough supplies to survive two-weeks after a major quake; however, Gabel notes Oregonians should prepare beyond two weeks.
“We can't prevent the next tsunami, but we can prepare for it, and the coast is a beautiful place to visit and live, and we encourage discussion of Cascadia, not to alarm people, but to encourage them to be informed and feel empowered to come to the coast with that knowledge in mind and enjoy themselves,” Gabel said.