: A Mild Shake in Southern California: Understanding the Recent 4.2 Magnitude Earthquake
Southern California experienced a gentle shake on Wednesday night as a magnitude 4.2 earthquake rolled through the region, centered in San Bernardino. The tremor, which occurred at 7:43 p.m., caused light shaking across various areas including Riverside, Fontana, Rialto, Rancho Cucamonga, Moreno Valley, and Redlands, according to reports from the U.S. Geological Survey.
Describing the intensity of the shaking, it’s likened to the sensation of a heavy truck striking a building, as per the Modified Mercalli Intensity Scale. Although Colton, situated just about a mile from the epicenter, felt the shaking more distinctly, authorities reported no urgent calls for assistance as of 9 p.m. This sentiment was echoed by law enforcement agencies in Rialto, located approximately two miles from the quake’s center.
Reports of weaker shaking trickled in from various parts of the region, including Los Angeles, Long Beach, and Orange County. Residents took to social media to share their experiences, mentioning sensations felt in Ontario, Yorba Linda, downtown Los Angeles, and even as far as Rowland Heights, where one resident described a sensation akin to being on a rapidly moving boat for about 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. Interestingly, the quake initiated just east of the mapped traces of the San Jacinto fault, known as one of the area’s most active and potentially hazardous fault lines.
The San Jacinto fault stretches approximately 130 miles from the Cajon Pass in San Bernardino County southeast toward the Mexican border, traversing through densely populated areas such as San Bernardino, Colton, Moreno Valley, Redlands, Loma Linda, Hemet, and San Jacinto. It also skirts near Riverside, Rialto, and Fontana, making it a point of concern for earthquake scientists.
The vulnerability of the Inland Empire to earthquakes is further accentuated by a lack of seismic retrofitting. Despite decades of warnings, a significant number of old brick buildings in cities like Riverside, Pomona, and San Bernardino remain unretrofitted, posing potential risks in the event of a major earthquake.
Seismologist Lucy Jones weighed in on the depth of Wednesday’s earthquake, noting that its depth of more than nine miles was relatively deep. While this quake occurred about 15 miles southeast of a previous one that shook the area on Jan. 5, Jones mentioned that they likely occurred on the same fault but were sufficiently distant in both time and space to not exhibit a clear correlation.
This recent earthquake marks Southern California’s first earthquake of at least magnitude 4 for the year, following a similar event on New Year’s Day off the Los Angeles County coast. On that occasion, a magnitude 4.1 earthquake struck about 10 miles southwest of San Pedro and 11 miles southeast of Rancho Palos Verdes.
Putting things into perspective, an average of 25 earthquakes with magnitudes ranging from 4.0 to 5.0 occur annually in California and Nevada, based on a recent three-year data sample.
If you experienced this earthquake, you’re encouraged to report your observations to the U.S. Geological Survey. Additionally, for those residing in earthquake-prone areas, it’s essential to familiarize yourself with safety protocols both before and during an earthquake. Consider signing up for resources like the Unshaken newsletter, which offers comprehensive guidance on emergency preparedness over six weeks, covering topics such as earthquake kits, essential apps, and insights from experts like Lucy Jones.
It’s worth noting that this article was not only generated by Quakebot, a computer application designed to monitor earthquake data from the USGS, but was also reviewed by a Times editor prior to publication. If you’re curious about the Quakebot system, you can explore a list of frequently asked questions for more information.