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,[7] causing only minor damage.[8] 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, and location suggest a likely source within the subducting Gorda Plate.[4] Despite being centered offshore, the fault that triggered the quake travelled onshore and ruptured northeasternwards.[9]
Following the mainshock, over 250 aftershocks above magnitude 1.0 occurred, distributed along a distance of 26 km (16 mi).[10][9] The largest aftershock of the year measured 4.9 magnitude with a maximum intensity of V (Moderate).[11] On January 1, 2023, a magnitude 5.4 aftershock struck, with a maximum intensity of VII.[12] 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.[13] A magnitude 4.5 earthquake struck six miles west-southwest of Ferndale on March 21 and was attributed as an aftershock by the USGS.[14]
Two people died due to "medical emergencies" involved with the earthquake, and seventeen others were injured.[3] 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.[15][16]
Damage
[edit]A damaged bridge ramp at Fernbridge near Ferndale.
Initial reports (via radio scanner traffic) indicated several houses were damaged, numerous gas leaks, and power outagesinRio Dell.[17] Fifteen buildings collapsed or were severely damaged, including one in a fire caused by the tremors.[18][19] 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.[20] A total of up to 150 homes were damaged or destroyed due to the quake, most of them in Rio Dell.[18]
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.[27] The National Oceanic and Atmospheric Administration (NOAA) did not issue a tsunami alert and no tsunami occurred.[28]
This article incorporates text from this source, which is in the public domain.
