On Wednesday night, Southern California experienced a 4.2 magnitude earthquake that was felt across a broad area.
The epicenter of the earthquake was in San Bernardino and it occurred at 7:43 p.m., causing mild tremors throughout the Inland Empire. This includes areas such as Riverside, Fontana, Rialto, Rancho Cucamonga, Moreno Valley, and Redlands, as reported by the U.S. Geological Survey.
The Modified Mercalli Intensity Scale describes the light shaking felt as similar to the impact of a heavy truck hitting a building.
Colton, located approximately a mile from the epicenter, also experienced the tremors. However, as of 9 p.m., the police had not received any calls for assistance, according to Sgt. Mike Farcas. The San Bernardino County Sheriff’s Department and the Rialto police, which is about two miles from the epicenter, confirmed this.
Mild tremors from the 4.2 magnitude earthquake were reported across Southern California, including Los Angeles, Long Beach, and Orange County. Social media posts indicated that the shaking was also felt in Ontario, Yorba Linda, and downtown Los Angeles. A resident from Rowland Heights likened the experience to being on a rapidly waving boat for three seconds.
The earthquake’s epicenter was located 1.5 miles southwest of downtown San Bernardino and half a mile north of the San Bernardino Depot train station. It originated just east of the San Jacinto fault, one of the most active and potentially hazardous fault lines in the region.
The San Jacinto fault, stretching about 130 miles from the Cajon Pass in San Bernardino County southeast towards the Mexican border, is a cause for concern among seismologists. It runs through the heart of the Inland Empire, passing through several cities including San Bernardino, Colton, Moreno Valley, Redlands, Loma Linda, Hemet, and San Jacinto, as well as near Riverside, Rialto, and Fontana.
The Inland Empire is particularly susceptible to earthquakes due to a lack of seismic retrofitting. A 2018 Times investigation revealed that hundreds of old brick buildings across more than a dozen cities in the Inland Empire, including Riverside, Pomona, and San Bernardino, were identified as hazardous but remained unretrofitted despite years of warnings.
Seismologist Lucy Jones noted on social media that the depth of Wednesday’s earthquake, over nine miles, was quite significant. The recent quake occurred about 15 miles southeast of a magnitude 4.2 earthquake that hit near the remote community of Lytle Creek in the San Gabriel Mountains of San Bernardino County on January 5.
Jones suggested that the two quakes likely occurred on the same fault, but their temporal and spatial separation makes a clear correlation difficult to establish.
The first earthquake of at least magnitude 4 this year in Southern California happened on New Year’s Day, off the coast of Los Angeles County. The 4.1 magnitude earthquake was centered about 10 miles southwest of San Pedro and 11 miles southeast of Rancho Palos Verdes.
On average, California and Nevada experience about 25 earthquakes with magnitudes ranging from 4.0 to 5.0 each year, based on recent three-year data.
If you felt this earthquake, you might want to consider reporting your experience to the USGS