Elleda Wilson: 'Yes, they happen here'
Jan. 27—Wednesday was the 322nd anniversary of the Jan. 26, 1700 megathrust 9-plus earthquake on the Cascadia Subduction Zone that, along with the tsunami that ensued, devastated much of the West Coast.
The subduction zone ruptured along its full length of over 600 miles, and the shaking lasted for several minutes, causing coastal land to suddenly drop and become flooded with seawater.
The Native Americans who survived the catastrophic event preserved the memory — and tried to explain what happened — by creating a colorful oral history. For example, the Quileute and the Hoh describe a horrific battle between Thunderbird and Whale; the mountains shook, and the ocean rose and covered the land.
Nine or 10 hours after the shaking stopped on the West Coast, a tidal wave hit Japan, and observers there were puzzled by the "orphan tsunami." The wave didn't seem to have any local cause. Nonetheless, the time, date and details were fastidiously recorded in several municipalities. It took 300 years for scientists and historians in the U.S. and Japan to connect the 1700 orphan tsunami with the catastrophic event on the Cascadia Subduction Zone.
Remnants of the disaster are visible on the North Coast to this day. One reminder is the Neskowin Ghost Forest. The trees, 150 to 200 feet tall, disappeared when the land suddenly dropped, and they were covered with debris. Stumps, more than 2,000 years old, according to carbon dating, appeared occasionally on the beach over the years, then reemerged for good during the winter of 1997-1998.
Closer to home, at the mouth of the Lewis and Clark River, researchers excavated a small section of the river bank, revealing a history of tsunami inundations. "The key message is: Yes, they happen here," Patrick Corcoran of the Oregon Sea Grant warned. "It's easy to be complacent ... We get large earthquakes and tsunamis fairly regularly in geologic time. The dates of these tsunamis are roughly 1700, 1400, 900 and 400 A.D."
So when will the next Cascadia "big one" hit? The Oregon Office of Emergency Management estimates there is "about a 37% chance that a megathrust earthquake of 7.1-plus magnitude in this fault zone will occur in the next 50 years." Are you ready?
