Much of history is lost to us because, for various reasons, we lack written records. Sometimes records are lost or destroyed, but many cultures passed stories from generation to generation rather than writing them down. That explains why we were so late in coming to certain realizations.
This week in The New Yorker there is an article, “The Really Big One”, about the earthquake danger to the coastal Pacific Northwest of the United States. It’s a terrifying article if you live in that area, especially when we learn that there already was a huge earthquake and tsunami in that area in 1700. But what I found most interesting was that science was used to help fill the gaps in historical knowledge. Or history was used to fill gaps in scientific knowledge.
On the science side, this is all new stuff, just discovered in the last half century. I don’t want to misinform you about the science, and can’t explain it succinctly, so if you are interested in how the science part works, read the article or start up your favorite search engine and take a look around. Much detailed information is widely available.
The part of this that I want to write about begins with the discovery in about 1970 of the Cascadia Subduction Zone (CSZ) on the western coast of North America. What I understand is that subduction zones line the Pacific Ring of Fire, and most of them are pretty active, regularly causing minor earthquakes. They also have the capacity to cause megathrust earthquakes and tsunamis, as happened in Indonesia in 2004 and Japan in 2011. That hasn’t happened with CSZ, which is one of the reasons it was a bit of a surprise that this subduction zone even existed.
On the history side of this mystery is the lack of historical records. Until the early 1800s, more than 100 years after the last big Pacific Northwest earthquake, the only people in that area were Native Americans. Their history was oral rather than written, and modern scientists and historians don’t give much credence to that type of evidence. In the two centuries since people other than Native Americans moved into the area and started keeping track of stuff, there hasn’t been a lot of shaking going on.
In the 1970s scientists wondered if the newly discovered CSZ had always been as silent as the last couple of centuries. But it took until the 1980s before several scientists found the key to this mystery in ghost forests, groups of trees that were standing but had all obviously died at the same time. Seeing the last growth ring was formed in 1699, and understanding how plants grow, it was clear they died sometime in 1699 or 1700. But that wasn’t enough to confirm an earthquake happened at that time.
Now they had some of the science, they needed to dig around in the history. Luckily for researchers, Japan has about 1400 years of historical records about earthquakes and tsunamis, and knew that the two events usually occurred in combination. Records show that in January of 1700, Japan had what they called an orphan tsunami, one for which they couldn’t identify the source earthquake.
By using science and history together, they were able to date the last big CSZ earthquake and tsunami to 1700. There’s always more to learn, in science and in history, and both specialties can work together to achieve understanding that benefits all.
Time is an interesting aspect of this. There were no written witness accounts to verify the earthquake that struck a mere 315 years ago. And if this research were being done 200 years ago, we would not have had access to the Japanese earthquake and tsunami records.
This is knowledge that impacts not only our understanding of our past, but also our present and our future. While we don’t know exactly when a future catastrophic event will happen, this new knowledge makes very clear that now is the time to start preparations. Who knows, maybe science and history working together can save the world.
You might want to check out these books:
Cascadia’s Fault: The Coming Earthquake and Tsunami That Could Devastate North America by Jerry Thompson Amazon
The Next Tsunami: Living On a Restless Coast by Bonnie Henderson Amazon
The Orphan Tsunami of 1700: Japanese Clues to a Parent Earthquake in North America by Brian F. Atwater Amazon