A moderate 4.2 magnitude earthquake struck Southern California on Wednesday evening, rattling homes and buildings across the Inland Empire region. The quake occurred at approximately 7:43 PM local time with an epicenter located 3 miles southwest of downtown San Bernardino in San Bernardino County, according to the United States Geological Survey (USGS).
The shaking emanating from the earthquake’s epicenter was felt in communities across the Inland Empire and beyond. Reports indicate light to moderate shaking was felt in cities including San Bernardino, Colton, Rialto, Fontana, Riverside, Rancho Cucamonga, Ontario, Moreno Valley, and Redlands. Weaker shaking from the quake extended as far as Downtown Los Angeles, Long Beach, and parts of Orange County.
Residents living near the epicenter described the shaking as strong enough to rattle household items, with the quake lasting for up to 10 seconds in some areas. The San Bernardino Police Department stated they did not receive any emergency calls related to injuries or damage from the earthquake.
Seismologists classify this week’s earthquake as a moderate event, capable of causing minor damage to poorly secured objects. The quake occurred at a depth of around 9 miles underground, considered relatively deep for California quakes. Deeper quakes tend to be widely felt at the surface but result in less intense ground shaking than shallower quakes, lowering potential damage.
Preliminary analysis indicates the earthquake likely occurred along the San Jacinto Fault zone, which spans approximately 130 miles from the Cajon Pass in San Bernardino County to the Mexican border. The San Jacinto Fault is considered one of the most active and potentially dangerous fault lines in Southern California, capable of producing damaging earthquakes of magnitude 7 or greater.
Segments of the fault run directly beneath heavily populated areas of San Bernardino, Moreno Valley, Hemet, and San Jacinto. The San Jacinto Fault has not experienced a major rupture since the late 1800s, leading seismologists to warn that strain continues building along the fault, increasing the risk of a large earthquake.
This week’s 4.2 magnitude quake struck in nearly the same location as a 4.2 magnitude earthquake on January 5th, also centered near San Bernardino. While the proximity of the two quakes is notable, seismologists state the events were likely isolated incidents and not foreshocks preceding a larger seismic event.
The greater Southern California region is seismically active and experiences frequent small to moderate earthquakes. On average, Southern California registers about 25 earthquakes in the magnitude 4.0-5.0 range annually. While many quakes in this range cause little damage, they serve as an important reminder for California residents to be prepared for larger, potentially catastrophic seismic events.
Residents are advised to secure heavy furniture and appliances, store emergency supplies, and retrofit older homes to withstand strong shaking from future quakes. Homeowners can also purchase earthquake insurance to help recover from potential property damage and loss from seismic activity. Following proper earthquake preparedness steps can help reduce injuries and disruption when the next major quake inevitably strikes Southern California.