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#  Megaquake Could Permanently Reshape Nor Cal Coast, New Study Warns

May 01 2025

Written by CalMatters.org.

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EARTHQUAKE - Scientists and government officials have long warned of climate-induced sea level rise along California’s coast. But a single event could eclipse those gradual changes, reshaping the entire region overnight.

[A new study](https://www.pnas.org/doi/10.1073/pnas.2424659122) describes the nightmare scenario that would unfold in the event of a major earthquake along the Cascadia Subduction Zone (CSZ). The CSZ runs from Cape Mendocino in Northern California through Oregon and Washington, all the way to Vancouver Island in British Columbia.

According to the new study published Monday in “Proceedings of the National Academy of Sciences,” an 8.0 earthquake or higher could permanently sink land by 1.6 to 6.6 feet and produce an immediate three-foot sea level rise. The area’s flood plain would increase 168%, more than doubling flood risk. This would lead to “compromised roadways and bridges” and cause “profound, lasting impacts to coastal populations, infrastructure, and ecosystems.” Humboldt Bay — including the cities of Eureka, Arcata, and Fortuna —would never be the same.

The last major earthquake on the CSZ occurred 325 years ago. The 9.0-magnitude quake sank entire towns. If it happened again, FEMA estimates it would immediately kill 5,800 people. Another 8,000 would perish in the ensuing tsunami.

The authors of the study hope state and local officials will use the new information to plan for the aftermath of a large Nor Cal quake. They advise officials to consider whether critical infrastructure would fall within the new post-quake flood plain. They also caution against building new schools, fire stations or wastewater plants in areas that would be highly susceptible to flooding after a megaquake.

*(This article was first published in California City News.)*

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