Where Earthquakes Have Happened
THE SIZE, LOCATION and how often earthquakes occur give an indication of what to expect in the future.
Since the mid-1800s, more than 40 earthquakes of M 6 or larger have occurred in California north of Santa Rosa and in adjacent offshore areas.
Not all earthquakes that affect Northern California are centered here. Great earthquakes like the 1964 M 9.2 Alaska earthquake may generate tsunamis that can hit our coast.
Ferndale after the 1906 earthquake.
Bricks from the same building fell during the April 1992 earthquake. The building has now been replaced by a wooden structure.
Notable earthquakes
January 26, 1700 Cascadia subduction zone – M 9 earthquake ruptured from Cape Mendocino to Vancouver Island—based on North American geology and Native American oral history. Japanese documents describe some of the ensuing tsunami’s effects on the far side of the Pacific.
April 18, 1906 San Andreas fault – M 7.8 earthquake ruptured from Santa Cruz to Shelter Cove, the largest Northern California earthquake in the past 200 years. Often called the San Francisco earthquake, it caused major damage in the coastal counties as far north as Humboldt and was felt throughout the state.
June 6, 1932 Gorda plate fault – M 6.4 earthquake centered near Arcata caused severe damage in the Humboldt Bay region and killed a woman in Eureka when a chimney from a neighboring building collapsed on her home.
December 21, 1954 Coastal onshore fault – M 6.5 earthquake located between Blue Lake and Willow Creek caused damage in the Humboldt Bay region and killed a man in Korbel.
November 8, 1980 Gorda plate fault – M 7.2 earthquake located offshore of Trinidad caused a highway overpass to collapse, and seriously injured six people driving on the bridge. $2 million in property damage; felt from Eugene, Oregon to San Francisco and Western Nevada.
April 26-27, 1992 Mendocino triple junction area – M 7.2, 6.7, 6.6 earthquakes caused hundreds of injuries, landslides, and major damage to buildings in Southern Humboldt County. The second earthquake caused a fire that destroyed Scotia’s business district. Coastal uplift produced a small tsunami that was recorded as far away as Hawaii. $66 million in damage; felt from Southern Oregon to Salinas and Redding.
September 21, 1993 Basin and Range fault – Two M 6 earthquakes centered near Klamath Falls in Southern Oregon damaged more than 1,000 buildings. Two people died, $7.5 million in damage; felt throughout Southern Oregon and in Northern California.
September 1, 1994 Mendocino fault – M 7 centered 90 miles offshore of Cape Mendocino. No damage; felt from Southern Oregon to San Francisco and caused tall buildings to sway in Sacramento. A three-inch tsunami was recorded in Crescent City.
January 9, 2010 Gorda plate fault – M 6.5 centered 30 miles offshore of Eureka. The earthquake caused about $20 million in damage to structures in Eureka and was felt from Eugene, Oregon to south of the San Francisco Bay Area.
Northern California earthquakes between 1970 and 2009.
How big is big?
Magnitude is one way to measure the size of an earthquake. Each unit of magnitude corresponds to about 32 times more energy released. An M 7 earthquake releases 32 times more energy than an M 6, and about 1000 times more than M 5. Both the area affected by the earthquake and how long the shaking lasts increase with magnitude. An M 4 will be felt only close to the epicenter and will last a few seconds. An M 7 will be felt by people hundreds of miles away and last 20 seconds or longer. Intensity is another way to estimate earthquake size. It measures how strongly the ground shakes in a particular location. If you feel an earthquake, you can help determine the intensity by reporting your observations at earthquake.usgs.gov/earthquakes/dyf
Recent Earthquakes don't tell the whole story
The first seismographs were installed in California just over 100 years ago and written records only go back as far as the mid-1800s. For evidence of earlier earthquakes, scientists look for geologic clues such as surface fault rupture and tsunami deposits, oral history of native peoples and written records from distant areas that were affected by a Northern California-generated tsunami. The study of ancient earthquakes is called paleoseismology.