This became known as the “orphan tsunami.”Īs outlined in a 1996 article in Nature, seismologist Kenji Satake and three colleagues were able to put all the pieces together, pulling from previous work by Atwater and Yamaguchi. According to these records, a six-hundred-mile-long wave struck the coast of Japan in January 1700, yet no earthquake was felt beforehand. The Japanese have kept written historical records of earthquakes and tsunamis for hundreds of years. The answer to this next piece of the puzzle was 5,000 miles away in Japan. With this timeline, Yamaguchi and Atwater concluded that a massive earthquake had occurred sometime between August, 1699 and May, 1700, causing the land to drop suddenly and the cedars to drown.īut could it be proven that this earthquake actually occured? The “Orphan Tsunami” They “took samples of the cedars and found that they had died simultaneously: in tree after tree, the final rings dated to the summer of 1699” explains Schulz. Atwater theorized that the trees died quickly when the ground beneath them plummeted underwater.Ītwater teamed up with Yamaguchi, a specialist in dendrochronology (the study of tree rings). But, this theory changed when Atwater was studying soil layers along the Washington coast and found evidence of sudden land subsidence. Scientists already knew these trees died from saltwater flooding, but they originally believed that the trees died slowly over time due to sea level rise. The clue? A grove of western red cedars known as the “ghost forest” on the banks of the Copalis River, near the Washington coast. The “Ghost Forest”Īs outlined by Schulz in her article, a clue was found in the 1980s by Brian Atwater, a geologist with the United States Geological Survey, and David Yamaguchi, a graduate student. This is because human settlements in the Pacific Northwest did not keep written historical records until the 1800s. Yet, scientists did not know if the Cascadia Subduction Zone had ever produced a strong earthquake, how often, or when the next one could occur. The Pacific Northwest sits squarely on the Ring of Fire, and this is why scientists first discovered the Cascadia Subduction Zone. In her article, Schulz explained the process scientists went through to discover the Cascadia Subduction Zone and its history of earthquakes. “The discovery of the Cascadia subduction zone stands as one of the greatest scientific detective stories of our time.” – Kathryn Schulz, author of The Really Big One.
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In comparison, the upper limit for the San Andreas Fault is a Magnitude 8.2. The “Really Big One”Ī New Yorker article, authored by Kathryn Schulz, gave this potential megathrust earthquake in the Pacific Northwest a name: “The Really Big One.” The next big earthquake in the Cascadia Subduction Zone will have a Magnitude as high as 9.2. In fact, the largest recorded earthquake in history was a subduction zone earthquake along the Ring of Fire, the 9.5 magnitude Valdivia Earthquake that struck Chile in 1960. Subduction zones create the largest-magnitude earthquakes in history, known as “megathrust” earthquakes. The Ring of Fire is actually a string of subduction zones. Global Earthquakes M7.0+ (depth 0–69km) along the Ring of Fire between 1900-2013 from USGS. It is well known that most or the world’s earthquakes occur on the Ring of Fire, which runs from the coasts of New Zealand, Indonesia, and Japan, to the west coast of North and South America.
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The north end of the subduction zone terminates near Vancouver Island, Canada. The south end of the subduction zone is near Cape Mendocino, California. The Cascadia Subduction Zone spans 700 miles north-to-south, off the coast of Oregon and Washington.
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The name “Cascadia” refers to the Cascade Range, a chain of volcanic mountains that are 100 miles inland, but follow a parallel path as the subduction zone. In the Pacific Northwest, the Juan de Fuca plate is colliding into the North American plate known as the Cascadia Subduction Zone. In comparison, the San Andreas Fault in California is an example of where two plates slide past each other at the surface, also known as a strike-slip fault.
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At the Cascadia Subduction Zone, the Juan de Fuca plate is colliding into the North American plate and descending beneath it. Subduction zones are where two plates collide against each other, with one plate descending beneath the other. The Cascadia Subduction Zone Subduction Zone Earthquakes The Pacific Northwest is the most dangerous earthquake hotspot outside of California – because it is part of the Cascadia Subduction Zone. While the San Andreas Fault has the potential to unleash a devastating earthquake ( the ‘big one” earthquake) at any moment, it’s not the only dangerous fault line in America – or even on the West Coast. Most Americans know only one fault line by name– the San Andreas Fault.