A recent study conducted by the University of Arizona has revealed a previously unknown earthquake threat to the Pacific Northwest. By examining tree rings, the researchers were able to identify a significant seismic event that took place in the Puget Lowlands in western Washington around late A.D. 923 or early 924. This discovery has raised concerns about the potential devastation that such an earthquake could cause in the region.
The study found that similar shallow faults located less than 18 miles below the surface ruptured about 1,000 years ago, similar to recent earthquakes in the Turkey-Syria border area. These earthquakes, with magnitudes of 7.8 and close to that, resulted in the destruction of thousands of buildings and the loss of over 50,000 lives. Now, it appears that the Pacific Northwest is facing a similar earthquake threat.
The researchers estimate that over 4 million residents in the Pacific Northwest, including major cities like Seattle, Tacoma, and Olympia, are at risk. The study also revealed that the shallow faults in the region are interconnected, either through subterranean connections or stress transfer from one fault to another. This finding has led the researchers to suggest that current regional hazard models need to be updated to include this earthquake threat.
Scientists have been aware of the presence of shallow faults in the region since the 1960s, but it was previously unclear when and how these faults last ruptured. The study utilized tree stumps that died during previous seismic events to determine the timing of these earthquakes. By comparing the growth patterns of ancient trees with those still living, the researchers were able to determine that the seismic events occurred in late fall through early spring of late 923 to early 924.
The research highlights the need for improved understanding and preparedness in the face of this earthquake threat. It also serves as a reminder of the importance of continuously updating hazard models to accurately assess the risks posed by natural disasters.
– University of Arizona study, led by Professor Bryan Black
– Published in the journal Science Advances