A magnitude 4.2 earthquake shook a wide swath of Southern California on Wednesday night.
The earthquake, centered in San Bernardino, struck at 7:43 p.m. and caused light tremors throughout the Inland Empire, including Riverside, Fontana, Rialto, Rancho Cucamonga, Moreno Valley and Redlands, according to the United States Geological Survey.
A slight tremor is defined by the Modified Mercalli Intensity Scale as the sensation of a heavy truck colliding with a building.
Colton suffered a tremor about a mile from the earthquake's epicenter. Police, however, had “not received a single call” for help around 9 p.m., the sergeant said. Mike Farcas told the Times. The San Bernardino County Sheriff's Department and police in Rialto, located about two miles from the center of the earthquake, echoed that statement.
Weaker tremors were felt throughout the region, including Los Angeles, Long Beach and Orange County. Residents said on social media that the tremor was sense in Ontario, Linda Yorba and Center of Los Angeles. One Rowland Heights resident said she felt three seconds of shaking, as if she were on a boat with fast-moving waves.
The epicenter was 1.5 miles southwest of downtown San Bernardino and a half mile north of the San Bernardino Depot train station. The earthquake began just east of the mapped traces of the San Jacinto Fault, one of the most active and potentially dangerous faults in the region.
The San Jacinto Fault spans approximately 130 miles and extends from Cajon Pass in San Bernardino County southeast toward the Mexican border. The San Jacinto Fault is one that worries seismic scientists because it cuts through the center of the Inland Empire, through cities such as San Bernardino, Colton, Moreno Valley, Redlands, Loma Linda, Hemet and San Jacinto, as well as near Riverside, Rialto. and Fontana.
The Inland Empire is also particularly vulnerable to earthquakes due to a lack of seismic modernization. A Times investigation published in 2018 said there were hundreds of old brick buildings in more than a dozen Inland Empire cities, including Riverside, Pomona and San Bernardino, that had been flagged as dangerous but had not been modernized despite of decades of warnings.
On social media, seismologist Lucy Jones said the depth of Wednesday's quake, more than 14 kilometers below the surface, was “pretty deep.” The latest earthquake occurred about 15 miles southeast of one that struck the area on Jan. 5, when a magnitude 4.2 earthquake began near the remote community of Lytle Creek in the San Gabriel Mountains of San Bernardino County. .
“The two earthquakes are likely due to the same fault, but are separated enough in time and space to have no obvious correlation,” Jones wrote on social media.
The first earthquake of at least magnitude 4 in Southern California this year occurred on New Year's Day, off the coast of Los Angeles County. That magnitude 4.1 earthquake was centered about 10 miles southwest of San Pedro and 11 miles southeast of Rancho Palos Verdes.
An average of 25 earthquakes with magnitudes between 4.0 and 5.0 occur per year in California and Nevada, according to a recent three-year data sample.
Did you feel this earthquake? Consider reporting what you felt to the USGS.
Find out what to do before and during an earthquake near you by signing up to our Unbreakable Newsletter, which breaks down emergency preparedness into small steps over six weeks. Learn more about earthquake kits, the apps you need, top tips from Lucy Jones, and more at latimes.com/Unshaken.
An earlier version of this story was automatically generated by Quakebot, a computer application that monitors the latest earthquakes detected by the USGS. A Times editor reviewed the post before publication. If you are interested in learning more about the system, visit our list of frequent questions.
