Preliminary 4.2-Magnitude Earthquake Shakes Southern California

A magnitude 4.2 earthquake centered in San Bernardino, Southern California, rattled a wide area on Wednesday night, prompting concerns due to its proximity to the active San Jacinto fault. The earthquake struck at 7:43 p.m., causing light shaking across the Inland Empire, including cities such as Riverside, Fontana, Rialto, Rancho Cucamonga, Moreno Valley, and Redlands.

The epicenter was located 1.5 miles southwest of downtown San Bernardino, near the San Bernardino Depot train station. The quake occurred just east of the mapped traces of the San Jacinto fault, which is known for its activity and runs through the Inland Empire, making it a cause for earthquake scientists' concern.

The San Jacinto fault, stretching about 130 miles from the Cajon Pass in San Bernardino County to the Mexican border, poses a potential threat to cities in its path, including San Bernardino, Colton, Moreno Valley, Redlands, Loma Linda, Hemet, and San Jacinto. The region is considered vulnerable due to a lack of seismic retrofitting.

Depth of the Earthquake

Seismologist Lucy Jones emphasized that the depth of the earthquake, exceeding nine miles, was considered "pretty deep." The earthquake was centered about 15 miles southeast of another quake that occurred on January 5, with a magnitude of 4.2, near the remote community of Lytle Creek in the San Gabriel Mountains of San Bernardino County.

"The two quakes are probably on the same fault, but they are far enough apart in both time and space to not have an obvious correlation," Jones stated.

The Inland Empire, marked by a lack of seismic retrofitting, raises concerns about the potential impact of earthquakes. A Times investigation in 2018 revealed hundreds of old brick buildings in the region that were designated as dangerous but remained unretrofitted, despite decades of warnings.

Southern California residents are reminded of the earthquake vulnerability as the region experienced its second quake of magnitude 4 or higher this year. On New Year's Day, a magnitude 4.1 earthquake occurred off the Los Angeles County coast.

Average Earthquake Frequency

On average, approximately 25 earthquakes with magnitudes of 4.0 to 5.0 occur annually in California and Nevada, based on recent three-year data samples.

While Wednesday's earthquake did not result in significant damage or injuries, the seismic activity underscores the ongoing seismic risks faced by Southern California residents, especially in areas with active fault lines and insufficient seismic retrofitting measures.