On December 20, 2022, a magnitude 6.4 earthquake struck Ferndale, California in Humboldt County, United States at 10:34:25 UTC, or 2:34 a.m. PST.

Tectonic setting

Much of

Northern California Northern California (colloquially known as NorCal) is a geographic and cultural region that generally comprises the northern portion of the U.S. state of California. Spanning the state's northernmost 48 counties, its main population centers incl ...

lies close to the boundaries between three tectonic plates, the

Pacific Plate The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At , it is the largest tectonic plate. The plate first came into existence 190 million years ago, at the triple junction between the Farallon, Phoenix, and Iza ...

, the Gorda Plate and the North American Plate, which meet at the Mendocino Triple Junction. The Mendocino Fracture Zone marks the transform boundary between the Gorda and Pacific plates. This tectonic boundary has been the cause of many earthquakes in the region, including the megathrust

1700 Cascadia earthquake The 1700 Cascadia earthquake occurred along the Cascadia subduction zone on January 26, 1700, with an estimated moment magnitude of 8.7–9.2. The megathrust earthquake involved the Juan de Fuca Plate from mid-Vancouver Island, south along the P ...

, and the

1992 Cape Mendocino earthquakes The 1992 Cape Mendocino earthquakes (or 1992 Petrolia earthquakes) occurred along the Lost Coast of Northern California on April 25 and 26. The three largest events were the M7.2 Fault (geology)#Dip-slip faults, thrust mainshock that struck near ...

, the latter of which measured 7.2.

Earthquake

The earthquake measured 6.4 on the moment magnitude scale, and had a maximum Mercalli intensity of VIII (''Severe''). It came exactly a year after a 6.2 magnitude earthquake struck onshore in the Cape Mendocino area on December 20, 2021, causing only minor damage. It was the result of strike-slip faulting along either a southeast or southwest striking plane. The United States Geological Survey said the earthquake's depth,

focal mechanism The focal mechanism of an earthquake describes the deformation in the source region that generates the seismic waves. In the case of a fault-related event it refers to the orientation of the fault plane that slipped and the slip vector and is ...

, and location suggest a likely source within the subducting Gorda Plate. Despite being centered offshore, the fault that triggered the quake travelled onshore and ruptured northeasternwards.

Aftershocks

Following the mainshock, over 250

aftershock In seismology, an aftershock is a smaller earthquake that follows a larger earthquake, in the same area of the main shock, caused as the displaced crust adjusts to the effects of the main shock. Large earthquakes can have hundreds to thousand ...

s above magnitude 1.0 occurred, distributed along a distance of . The largest aftershock of the year measured 4.9 magnitude with a maximum intensity of V (''Moderate''). On January 1, 2023, a magnitude 5.4 aftershock struck, with a maximum intensity of VII. Broken windows, large cracks in buildings and power outages were reported in Humboldt County due to this aftershock, and some houses were badly damaged after being shaken from their foundations. A magnitude 4.5 earthquake struck six miles west-southwest of Ferndale on March 21 and was attributed as an aftershock by the USGS.

Impact

Casualties

Two people died due to "medical emergencies" involved with the earthquake, and seventeen others were injured. In both fatalities, ages 72 and 83, emergency workers were unable to attend to them because ambulances were responding to other areas. One of the deaths was related to a cardiac arrest.

Damage

Initial reports (via radio scanner traffic) indicated several houses were damaged, numerous gas leaks, and power outages in

Rio Dell Rio Dell ( Spanish: ''Río Dell'', meaning "Dell River") is a city in Humboldt County, California, United States. It is located on the west bank of the Eel River north of Scotia at an elevation of 161 feet (49 m). The population was 3,363 a ...

. Fifteen buildings collapsed or were severely damaged, including one in a fire caused by the tremors. About 100 people were displaced due to damaged homes. Glass windows in stores were shattered and homes knocked off their foundations. At Loleta, bricks toppled from the former Humboldt Creamery building. Some businesses in Fortuna and Ferndale sustained damage at storefronts and products fell. A total of up to 150 homes were damaged or destroyed due to the quake, most of them in

. Pacific Gas and Electric (PG&E) at first estimated that 50,000 people were without power in Humboldt County, a number later revised to 60,000. The California Independent System Operator (CAISO) declared a transmission emergency. Phones were alerted of the coming earthquake as far south as the San Francisco Bay Area. As of 4:25 am. PST, PG&E revised the total of customers without power to 71,170.

Caltrans The California Department of Transportation (Caltrans) is an Executive (government), executive department of the U.S. state of California. The department is part of the Government of California#State agencies, cabinet-level California State Tran ...

District 1 closed the Fernbridge over the Eel River on

California State Route 211 State Route 211 (SR 211) is a state highway in the U.S. state of California that connects Ferndale with U.S. 101 in Humboldt County. The highway was originally designed to be the northernmost segment of State Route 1, but after construction ...

due to four cracks which could cause the road itself to slide off. The California Office of Emergency Services (Cal OES) coordinated the responses of local governments (including tribal authorities), Cal Fire, Caltrans, the

California Geological Survey The California Geological Survey, previously known as the California Division of Mines and Geology, is the California state geology, geologic agency. History Although it was not until 1880 that the California State Mining Bureau, predecessor to ...

, and the California Highway Patrol.

Cal Poly Humboldt California State Polytechnic University, Humboldt also known as Cal Poly Humboldt, Humboldt or Cal Poly"Cal Poly" may also refer to California Polytechnic State University in San Luis Obispo, California or California State Polytechnic Universit ...

University was closed to all except essential personnel as of 7:16 am.

Response

The earthquake activated ShakeAlert, USGS's earthquake early warning system for the West Coast. Three million people in northern California and southern Oregon received warnings on their smartphones. Sensors at Fortuna detected the earthquake at 02:34 and issued warnings as far as the California–Oregon border, south of San Jose, past Shasta County and to Medford, Oregon. The warning issued was the most widespread since the system went public in 2019. The National Oceanic and Atmospheric Administration (NOAA) did not issue a tsunami alert and no tsunami occurred.

References

{{DEFAULTSORT:Ferndale earthquake, 2022 2022 earthquakes 2022 in California 2022 natural disasters in the United States December 2022 events in the United States Earthquakes in California Ferndale, California History of Humboldt County, California Power outages in the United States