4.3 magnitude quake shakes Humboldt County, no tsunami expected

A magnitude 4.3 earthquake struck about 80 miles southeast of Eureka on July 10 and was felt across the Humboldt County area. The National Tsunami Warning Center issued a tsunami information statement. No tsunami was expected.

The U.S. Tsunami Warning Centers use that alert when an earthquake has happened but the risk of a damaging wave is not expected. The warning centers rely on preliminary earthquake information to get messages out as early as possible, then local offices move them into the public alert system.

For Humboldt residents, the key distinction is between an information statement, an advisory, and a warning. An information statement means the quake was registered, but forecasters do not expect a tsunami. An advisory signals a more serious threat that can bring strong currents and dangerous surges. A warning is the highest level, and it means people in threatened coastal areas should move to higher ground or inland immediately.

The National Tsunami Warning Center serves the continental United States, Alaska and Canada. In northwest California, the National Weather Service office in Eureka passes those tsunami messages along locally and uses NOAA Weather Radio to distribute earthquake and tsunami information.

The National Weather Service office in Eureka says northwest California, especially near Cape Mendocino, is one of the most seismically active parts of the United States. About 25% of California’s annual release of seismic energy comes from that region, and since 1980 there have been five earthquakes close to magnitude 7.0 and six earthquakes of magnitude 6.0 or larger there.