Mega quake could trigger shaking on entire West Coast

[Auggie]

San Francisco Chronicle/ 10-12=2025

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.

The authors found evidence of 18 other large earthquakes on the Cascadia that preceded ones on the northern San Andreas over the past 3,000 years, said Patton, who along with lead author Chris Goldfinger has been studying the possible correlation between the two faults for more than 20 years. This latest study has the strongest evidence so far that earthquakes on the Cascadia Fault preceded those on the San Andreas, said Patton.

LINK (paywall): https://eedition.sfchronicle.com/infinity/article_popover_share.aspx?guid=898285b4-9a32-448d-9496-63d1888c0d4d&share=true

Highlights (from the link):

• The frequency of major quakes on the southern part of the Cascadia subduction zone — as large as magnitude 8.5 to 9 — happen on average every 220 years.

• The Cascadia subduction zone has a 37% chance of producing a large quake in the next half century and could set off tsunamis that could reach the Bay Area in hours.

• The frequency on the northern San Andreas Fault is an average of 200 years.

Quote (from the link): “If they (the faults) both went off together, then you’ve got potentially San Francisco, Portland, Seattle and Vancouver all in an emergency situation in a compressed timeframe,” said Goldfinger.

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Goldfinger?

[Turbineguy]

1. Trumpers can't wait.

[travelingthrulife]

2. Maybe our plate tectonics shift will make us Californians part of Canada.

Silver lining.

[MineralMan]

3. Yes, of course. We've known this all my life.

And yet, life goes on as if it were impossible.