The magnitude-6.4 quake struck within the Mendocino Triple Junction, where three tectonic plates meet. Because the junction is distorted and compressed, deformation is distributed across a network of faults, one of which ruptured on Dec. 20, 2022. 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. The arrows give the sense of motion of the faults. The color ramp gives the magnitude (within 100 kilometers) that’s likely in a lifetime. Note that likely maximum magnitude within 100 kilometers of the Mendocino region in a lifetime is magnitude 7.2.