The arrows give the sense of motion of the faults. Historically, the junction has been extremely seismically active, but fortunately it is more lightly populated and better prepared than most areas in the United States. Because the junction is distorted and compressed, deformation is distributed across a network of faults, one of which ruptured on Dec.
The magnitude-6.4 quake struck within the Mendocino Triple Junction, where three tectonic plates meet. The Ferndale and surrounding Cape Mendocino areas are laced by faults. The collisions lead to Earth’s crust being compressed and stretched, and that distortion is exacerbated by two factors: the Juan de Fuca Plate subducting (sliding underneath) unevenly under the North American Plate, and the 80-degree bend the San Andreas Fault makes when it juts out into the Pacific. Thankfully, it is not densely populated, and its residents and governments are well prepared for earthquakes.įerndale sits atop a geologic “triple junction,” where three tectonic plates collide - in this case, the North American, Juan de Fuca, and Pacific Plates are colliding in the Mendocino Triple Junction, shown in the figure below. Why is the Cape Mendocino area so seismically active?įerndale and the surrounding 60-by-60-mile (100-by-100-kilometer) area make up the most seismically active region of California, with one magnitude-6.4 or larger quake every decade, on average. But the severe rupture of a hidden, unmapped fault in this seismically active region nevertheless raises concern over current hazard risk assessments and methods that are based on mapped faults. That quake has about a 1% chance of occurring per year. This hyperactive seismic region has the strongest “once-in-a-lifetime” quake that can be expected compared to anywhere in the United States (even Alaska!): magnitude 7.2.
Scientifically, the quake was not a surprise: According to the Temblor model, there’s a 5% chance that a magnitude-6.4 earthquake will occur once per year in this region. Whether advance warning reached those within about 28 miles (45 kilometers) from the epicenter (those who experienced strong shaking) is not yet clear. These alerts ideally provide several precious seconds of notice to those who could experience strong shaking. The earthquake triggered an Earthquake Early Warning alert, issued by the U.S. As geologists began to analyze the event, they found landslides and cracks in roads - but no signs of liquefaction or, intriguingly, an obvious rupture at the surface (California Geological Survey, 2022). Severe shaking lasted for 15 to 20 seconds, leading indirectly to the deaths of two people, extensive building and infrastructure damage, and power blackouts throughout the region. 20, 2022, a magnitude-6.4 earthquake hit Ferndale, Calif. S., Toda, S., Rollins, C., and Sevilgen, V., 2023, December 2022 California earthquake ruptured unknown fault: an analysis, Temblor, Īt 2:34 a.m. Stein, Ph.D., Temblor, Inc., Shinji Toda, Ph.D., Tohoku University, Chris Rollins, Ph.D., GNS Science New Zealand, and Volkan Sevilgen, M.Sc., Temblor, Inc.Ĭitation: Stein, R. The quake produced severe shaking in a lightly populated area, brought the southern tip of the Cascadia Subduction Zone slightly closer to failure, and modestly inhibited rupture on the San Andreas Fault.īy Ross S.
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