Tiny Quakes Reveal a Five-Piece Tectonic Puzzle Under Northern California
Scientists report in Science (Jan 15, 2026) that undetectable low-frequency earthquakes beneath the Mendocino Triple Junction reveal a far more complex tectonic system than previously thought: five moving pieces instead of three, including a Pioneer Fragment dragged beneath the North American Plate and a subducting segment with the Gorda Plate. Using dense seismometer data and tidal triggering by the Sun and Moon, researchers formed a new five-piece model of plate interactions off Northern California, with implications for understanding seismic hazards and where fault boundaries actually lie.