Magnitude 5.6 Earthquake Shakes Redwood Valley, California; Strong Local Shaking and Aftershocks Expected

A magnitude 5.6 earthquake struck Wednesday morning just north of Redwood Valley in Mendocino County, producing very strong shaking near the epicenter, according to the U.S. Geological Survey. The quake hit at 8:10:40 a.m. PDT and was centered about 7 miles north of Redwood Valley at a depth of 5.01 miles, making it relatively shallow and more likely to generate strong local shaking. In the first roughly 20 to 25 minutes after the quake, no authoritative county, state, hospital or major-news confirmation of casualties, structural damage or emergency declarations was immediately available.

The USGS ShakeMap estimated maximum shaking at Modified Mercalli Intensity VII, which it classifies as “very strong.” Community reports submitted to the agency through its “Did You Feel It?” system reached MMI VIII in the hardest-hit areas. The epicenter was located at 39.364 degrees north, 123.229 degrees west, in inland Mendocino County. Redwood Valley is north of Ukiah, the county seat and nearest larger population center, which lies about 9 miles south of Redwood Valley.

Aftershocks are expected. The USGS routinely issues operational aftershock forecasts for U.S. earthquakes of magnitude 5 and above, and additional smaller quakes commonly follow an event of this size. Because the earthquake was centered inland rather than offshore, there is no tsunami threat under NOAA and USGS guidance.

The Mendocino region is one of California’s more seismically active areas because of complex faulting tied to the Mendocino Triple Junction, and the Ukiah-Redwood Valley area is also associated with the Maacama Fault system. Even so, official assessments were still pending Wednesday morning, and any information about damage or injuries had not yet been confirmed.