Magnitude 4.9 quake strikes off Northern California coast near Eureka

A magnitude 4.9 earthquake rattled the Northern California coast just before 10 p.m. Friday, striking offshore about 79 miles northwest of Eureka and 59 miles west-southwest of Crescent City. The U.S. Geological Survey placed the quake at a depth of 10.0 kilometers, close enough to be felt across parts of the North Coast but not severe enough to trigger a wider damage response.

USGS data showed a Community Internet Intensity of III, which points to weak shaking, and a PAGER rating of GREEN, the lowest risk category in the system. The agency had received five “Did You Feel It?” reports by the time of the event listing, and its aftershock forecast called for less than 1% odds of a magnitude 6 or larger aftershock, less than 1% for magnitude 5 or larger, 6% for magnitude 4 or larger, and 35% for magnitude 3 or larger over the next week.

No damage was immediately reported, and the quake landed in a region that Humboldt County officials regularly remind residents is one of the most earthquake-prone stretches of the continental United States. County preparedness materials point to the Mendocino triple junction and the 700-mile Cascadia Subduction Zone, a fault system capable of producing a magnitude 9 earthquake or stronger.

That larger threat is why even a moderate offshore shake draws attention in Eureka, Arcata, Fortuna, the Samoa Peninsula and other North Coast communities. The Humboldt County Sheriff’s Office of Emergency Services remains the county’s primary coordination agency for emergencies and disasters affecting residents, public infrastructure and government operations, and local officials stress that a strong Cascadia event could bring violent shaking, landslides and a destructive tsunami along the coast.

The region has lived through that danger before. The April 25, 1992 Cape Mendocino earthquake sequence began with a magnitude 7.2 mainshock near Petrolia, followed by magnitude 6.5 and 6.6 aftershocks the next day. The shaking damaged buildings, roads and bridges, triggered numerous landslides and led President George H.W. Bush to declare Humboldt County a major disaster area. Against that backdrop, Friday night’s quake looks more like a familiar reminder than a warning sign: North Coast seismic activity is normal, but every jolt is a chance to check supplies, review evacuation routes and make sure earthquake and tsunami plans are current.