A megaquake in the Pacific Northwest could trigger a large earthquake along California’s San Andreas Fault, creating an unprecedented catastrophe up and down the Pacific Coast, a new study has found.
The study suggests that the fearsome Cascadia subduction zone, a fault line running offshore from Northern California to British Columbia that is capable of producing earthquakes of magnitude 9 or higher, has triggered large quakes in San Francisco and elsewhere along the northern part of the San Andreas Fault. In some cases, it’s possible that quakes on the San Andreas followed the first quake within minutes or hours, according to the study, which was published Sept. 29.
For example, researchers found evidence that the last magnitude 9 earthquake in the Cascadia subduction zone — in 1700 and so large that it caused a tsunami in Japan — also produced a major earthquake on the northern San Andreas Fault. That part of the fault extends from the Mendocino Junction offshore of Humboldt County, where it meets the Cascadia, to Hollister (San Benito County). That earthquake could have been as large as the magnitude 7.9 earthquake in 1906 San Francisco, said Jason Patton, a co-author of the study and engineering geologist at the California Department of Conservation…