By Rong-Gong Lin II, Los Angeles Times
- New research suggests the San Andreas fault and the Cascadia subduction zone could produce devastating back-to-back earthquake disasters.
- Scientists found evidence that major Cascadia quakes were followed by large San Andreas earthquakes in 1700 and throughout the last 2,500 years.
They are two of the West Coast’s most destructive generators of huge earthquakes: the San Andreas fault in California and the Cascadia subduction zone offshore of California’s North Coast, Oregon, Washington, and British Columbia.
The public has often thought of these danger zones as separate entities.
But what if they were capable of back-to-back disasters?
That’s the unsettling possibility described in a groundbreaking new study published recently in the journal Geosphere.
The authors suggest that, for thousands of years, large earthquakes on the Cascadia subduction zone were quickly followed by large earthquakes on the northern San Andreas fault.
(John Wesley Powell Center for Analysis and Synthesis / USGS)
In 1700, a Cascadia subduction zone earthquake is believed to have measured around a magnitude 9. Based on archaeological evidence, villages sank and had to be abandoned, according to the U.S. Geological Survey. That earthquake was so powerful, entire sections of the Pacific coastline dropped by as much as 5 feet. In the Pacific Northwest, Native American stories told of “how the prairie became ocean” and canoes were flung into trees.
The study suggests the Cascadia earthquake was followed by a northern San Andreas fault earthquake from Cape Mendocino toward San Francisco, with a magnitude of around 7.9.
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