A humpback whale lobtails over Noyo Canyon in the Pacific Ocean approximately eight miles off of the Mendocino Coast, Calif., on Sunday, March 1, 2026. (Peter Pyle/Cal Geographic via Bay City News)

I just got the kind of one-word text you never want to get from your grown daughter working from home in Tacoma, Washington, with your new baby grandson on the floor playing next to her. “Earthquake!”

A magnitude 4.3 earthquake emanating from somewhere close to home in Mendocino County on the San Andreas Fault system is usually not more than an uncomfortable reminder of the ongoing volatility and fragility of our seismic landscape, but a 4.3 in Puget Sound can signify something deeper and more dangerous still to arise from the ominous Cascadia subduction zone complex.

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Rowena Forest is a physical geographer and science writer at Cal Geographic. To follow her in-depth explorations and investigations of California’s living landscapes, and for upcoming field trips please...