13 Earthquakes Strike Southern California in 25 Minutes

A series of 13 earthquakes struck Southern California within 25 minutes early Monday morning, centered northwest of El Centro near the Salton Sea, according to the United States Geological Survey (USGS). The shaking began just after midnight with a magnitude 4.8 quake, followed by a magnitude 4.5 aftershock six minutes later.

Over the next 19 minutes, 11 smaller quakes rattled the region. The quakes are believed to have originated from the active San Jacinto fault system. While no major damage has been reported, the cluster is another reminder that California sits squarely in earthquake country.

Overnight Earthquake Swarm Strikes Southern California

A series of 13 earthquakes rattled the southern region of California for 25 minutes during the early hours of Monday morning. According to the National Weather Service (NWS), the initial tremor registered at a 4.8 magnitude just after midnight northwest of El Centro, a city in the Imperial County vicinity of the southern California border.

The United States Geological Survey (USGS) recorded the first seismic event at 12:36 am, noting its epicenter was situated roughly 7 miles below the earth’s surface. The agency’s earthquake early warning system, ShakeAlert, was activated upon detecting the quake and delivered alerts to mobile devices via partner apps.

Swarm of California Tremors Attributed to Active Fault Lines in San Jacinto

Geologists have attributed the swarm of tremors to activity along the San Jacinto fault zone, one of Southern California’s most active fault lines. While light to moderate earthquakes frequently rattled the region, Monday’s quakes did not appear to cause any reported damage or injuries.

Most Californians are accustomed to frequent, minor earthquakes. Tremors ranging from 2.5 to 5.4 in magnitude are often perceptible but rarely destructive. Moderate quakes between 5.5 and 6.9 may lead to minor damage, especially in highly populated areas.

Details on the 13 Earthquakes in 25 Minutes

The southern California region experienced a series of earthquakes overnight, totaling 13 quakes in 25 minutes. According to the United States Geological Survey (USGS), the initial earthquake struck at 12:36 am on Monday, measuring a 4.8 magnitude on the Richter scale. The epicenter was approximately 11.7 miles below the surface, 2 miles northwest of El Centro, California.

Six minutes after the first earthquake, a 4.5 magnitude aftershock hit the same vicinity. This was followed by 11 smaller aftershocks over the next 19 minutes, ranging from 2.6 to 3.2 magnitude. The earthquakes are believed to have originated from the San Jacinto fault system, one of Southern California’s most seismically active fault lines.

First Tremor Activated The USGS ShakeAlert System

The USGS ShakeAlert system was activated upon detection of the first earthquake. The system estimated the initial quake to be 5.0 or higher, prompting alerts to be sent to mobile phones through emergency alert apps and services.

Minor earthquakes ranging from 2.5 to 5.4 magnitude are frequently felt but rarely cause damage. Moderate earthquakes of 5.5 to 6 magnitude may result in minor damage to structures. Major earthquakes of 6.1 magnitude and above can lead to severe damage, especially in highly populated areas.

Epicenter and Magnitude of the Main 4.8 Quake

The epicenter of the initial 4.8 magnitude earthquake was located approximately 11.7 miles below the surface, according to the USGS. The epicenter refers to the point on the earth’s surface directly above the hypocenter, which is the actual location below the surface where the earthquake rupture initiated.

This moderate 4.8 magnitude earthquake would have been felt over a large area but likely only caused minor damage. The depth of the initial quake below the surface likely prevented more severe damage at the epicenter.

Aftershocks Felt Across San Diego County

The aftershocks are believed to have originated from the San Jacinto fault zone, one of southern California’s most active fault lines. This fault system has produced damaging earthquakes and threatens future seismic activity.

Earthquake preparedness is critical for all residents of seismically active areas. Recommendations include securing heavy furniture, water heaters, and appliances to prevent toppling; developing and practicing emergency response and evacuation plans; storing essential supplies; and learning how to turn off gas, water, and electricity in the event of damage to infrastructure.

ShakeAlert System Activated to Warn Residents

Once the ShakeAlert system detects an earthquake, it determines the location and magnitude. It alerts partners who can activate warning devices like cell phones, radios, sirens, and message displays. The ShakeAlert system aims to give people time to take cover before strong shaking knocks them down or causes buildings and structures to collapse.

The ShakeAlert system estimated the initial quake that struck northwest of El Centro at 12:36 am on Monday to be above a magnitude 5.0, so alerts were delivered to cell phones through the MyShake app, FEMA’s Wireless Emergency Alerts system, the ShakeReadySD notification system in San Diego County and the Android Operating System.

Typical Magnitudes of Light vs Damaging Quakes

Light earthquakes, ranging from 2.5 to 5.4 on the Richter scale, are often felt but rarely cause damage. These minor tremors may rattle windows or dishes but typically do not disrupt daily life or activities. Communities located near the epicenter of light earthquakes will experience shaking for a few seconds up to around a minute.

Moderate earthquakes measuring between 5.5 to 6 on the Richter scale can result in slight damage to vulnerable buildings like mobile homes not secured to foundations. Major earthquakes of 6.1 to 6.9 magnitude may lead to considerable damage in highly populated areas.

Why California Experiences Frequent Earthquakes

California is a geologically complex region with numerous faults that make it prone to frequent earthquakes. The state straddles the boundary between the Pacific and North American plates, two of the earth’s tectonic plates. These plates are sliding past each other, which causes earthquakes along the fault lines.

The San Andreas fault system is one of California’s longest and most active fault systems. It runs for about 800 miles through the state, where the Pacific plate grinds northwestward past the North American plate.

The Tremors Might Be A Warning Sign

The series of earthquakes that struck Southern California overnight serves as a reminder of the active seismic hazards in the region. While these quakes caused little damage, their frequency over a short period underscores the need for preparedness and infrastructure built to withstand shaking.

As experts continue studying the causes and potential impacts, residents should review emergency plans and secure items in their homes. Though unsettling, episodes like these present an opportunity to improve safety and readiness for California’s inevitable larger earthquakes.