California's earthquake risk just got more complicated
Scientists have discovered that Northern California's Mendocino Triple Junction—where major fault lines meet—actually has five moving tectonic pieces, not three like everyone thought.
This could totally change how we look at earthquake risks in the region.
Hidden tectonic pieces revealed with micro-earthquake data
By tracking tiny, low-frequency earthquakes, researchers uncovered two "secret" fragments: the Pioneer Fragment (a leftover from an ancient plate now buried under North America) and a chunk of the North American Plate being pulled underground.
These aren't visible on the surface but play a big role deep below.
Why does this matter for earthquakes?
One of these hidden pieces—the Pioneer Fragment—might explain why some quakes, like the 1992 Cape Mendocino event, start closer to the surface than expected.
As researcher Kathryn Materna put it, these boundaries "deviate" from what scientists assumed.
What's next?
Co-author Amanda Thomas (professor of earth and planetary sciences at UC Davis) said, "If we don't understand the underlying tectonic processes, it's hard to predict the seismic hazard."
With this new info, scientists hope to improve earthquake forecasts and help keep Northern California safer.