26-Foot Tsunami Could Hit California Study looks at Cascadia Subduction Zone fault By Kate Seamons, Newser Staff Posted Mar 26, 2013 8:15 AM CDT 25 comments Comments With a tsunami warning in effect for Northern California, two men watch the waves at San Francisco's Ocean Beach on Friday, March 11, 2011. (AP Photo/Noah Berger) (Newser) – It's a frightening scenario: An infamous 620-mile fault located off the West Coast generates an 8.0-magnitude earthquake; it triggers a 26-foot tsunami that strikes northern California. According to a new study, that series of events is a real possibility, and would threaten more than a quarter of a million Californians. The US Geological Survey study, released to coincide with Tsunami Awareness Week, identifies the areas most likely to be hit, and puts a figure to them: 267,000 California residents live in "tsunami-inundation" zones, and another 169,000 work in them; and that's not counting the tourists. As AFP explains, the Cascadia Subduction Zone fault named in the study has produced at least seven tsunamis in the last three millennia, spaced as little as 140 years apart; the last occurred in 1700. "A future CSZ-related earthquake (likely magnitude 8 or larger) would create a series of tsunami waves possibly 8 meters ... or higher that would inundate these communities in 15 to 20 minutes after initial ground shaking," the study notes. Waves would hit Southern California "approximately one hour later."