Two Earthquakes, Centered in Ontario, Rattle Southern California

What Happened?

Two earthquakes, measuring 4.0 and 4.2 on the Richter scale, struck Southern California on Thursday, July 28, 2023, at approximately 10:30 a.m. Pacific Time. The epicenter of both earthquakes was located near the city of Ontario, about 40 miles east of Los Angeles.

Damage and Injuries

There were no reports of major damage or injuries from the earthquakes. However, some residents in the affected areas reported feeling shaking and hearing loud noises. A few buildings in Ontario were evacuated as a precaution, but no structural damage was found.

Aftershocks

Following the initial earthquakes, there were several smaller aftershocks in the area. The largest aftershock, measuring 3.0 on the Richter scale, occurred at 11:15 a.m. Pacific Time. Geologists expect aftershocks to continue for several days, but they are expected to diminish in frequency and intensity over time.

Cause of the Earthquakes

The earthquakes were caused by movement along the San Jacinto Fault, a major fault line that runs through Southern California. The San Jacinto Fault is known to be seismically active, and it has produced several large earthquakes in the past, including the 1999 Hector Mine earthquake and the 1992 Landers earthquake. Geologists say the earthquakes were likely triggered by stress building up along the fault as a result of the movement of tectonic plates.

Impact on the Region

The earthquakes caused some disruption to traffic and public transportation in Southern California. Several roads were closed due to rockfalls and landslides, and some public transportation lines were delayed or suspended due to safety concerns. A few schools in the affected areas were also closed early as a precaution.

Response from Authorities

Emergency management officials in Southern California are monitoring the situation and have deployed personnel to the affected areas to assess damage and provide assistance. The California Governor's Office of Emergency Services has activated its response plan and is coordinating with local authorities to provide support as needed.

Advice for Residents

Residents in Southern California are advised to be prepared for aftershocks and to take precautions to stay safe in the event of an earthquake. They should secure loose objects in their homes and workplaces, know where the nearest exits are, and have a plan for where to go if an earthquake strikes. They should also have a supply of food, water, and first aid supplies on hand.