May 16, 2013 10:11 am
In 1700, a massive earthquake struck the west and northwest coast of the United Sates. Modern scientists first caught wind of the natural disaster through the scars it left on the land—massive, toppled red cedar trees and sand deposits washed far inland. Written records weren’t being kept in that region when the earthquake happened, but several years ago, scientists managed to pinpoint the date of that mysterious earthquake. In 2005, Smithsonian explained how they unraveled the mystery:
In Japan, officials had recorded an “orphan” tsunami—unconnected with any felt earthquake— with waves up to ten feet high along 600 miles of the Honshu coast at midnight, January 27, 1700. Several years ago, Japanese researchers, by estimating the tsunami’s speed, path and other properties, concluded that it was triggered by a magnitude 9 earthquake that warped the seafloor off the Washington coast at 9 p.m. Pacific Standard Time on January 26, 1700. To confirm it, U.S. researchers found a few old trees of known age that had survived the earthquake and compared their tree rings with the rings of the ghost forest cedars. The trees had indeed died just before the growing season of 1700.
The earthquake occurred along the Cascadia Subduction Zone, a major fault line running from the Pacific Northwest to Vancouver. In recent decades, scientists have determined that this fault line may produce mega-earthquakes of 9.0 or higher on the Richter scale.
Considering all the geologic evidence, scientists now say a major earthquake strikes the Pacific Northwest every few hundred years—give or take a few hundred years. That means the next one could strike tomorrow.
This is why researchers hope to learn as much as they can, as quickly as they can about the devastating quake that rocked the land back in 1700. Earthquake prediction remains notoriously sketchy (just look at the recent example of researchers in Italy who failed to predict an earthquake in L’Aquila), so the more scientists can learn about what happened in the past, the better prepared they can be for the next disaster. And that next one could be coming soon, according to new research:
The Cascadia subduction zone is of particular interest to geologists and coastal managers because geological evidence points to recurring seismic activity along the fault line, with intervals between 300 and 500 years. With the last major event occurring in 1700, another earthquake could be on the horizon. A better understanding of how such an event might unfold has the potential to save lives.
The University of Pennsylvania team turned to a fossil-based technique for studying the Cascadia Subduction Zone. They took core samples throughout the region and then picked through the samples to find microscopic foraminifera fossils, a type of single-celled aquatic protist. They used radiocarbon dating to estimate the age of these ancient creatures and to recreate past changes in land and sea level along the coastline. Through their analyses, they saw that the coastline ruptured in a heterogenous manner, or that the earthquake struck in different locations with different severity.
The earthquakes that occurred in this part of North America, they report, behaved similarly to recent major earthquakes in Japan and Chile, which arrived with very little warning. While the results are useful for modeling and understanding the next West Coast mega-earthquake, the researchers warn that some areas in Oregon will likely have just 20 minutes to evacuate before the tsunami waves arrive.
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