M5.2 San Diego earthquake linked to Elsinore Fault renews concerns over major seismic risk in Southern California

The M5.2 earthquake that struck San Diego County on April 14 caused no injuries or major damage, but it drew renewed attention to the Elsinore Fault’s potential to generate much larger earthquakes. While historically quiet, the fault forms part of a complex system capable of producing cascading ruptures that could impact millions.

The Elsinore Fault Zone is a right-lateral strike-slip fault extending about 180 km (112 miles) through Southern California, running parallel to the San Andreas Fault and forming part of the broader San Andreas fault system. It cuts through the Peninsular Ranges and passes near several major population centers, making it a significant seismic hazard.

Despite appearing inactive, the fault holds the potential to generate a powerful M7.8 earthquake, according to Caltech seismologist Lucy Jones.

Stretching from the Sonoran Desert in Imperial County, the Elsinore Fault zone passes through the western parts of Riverside County, affecting cities such as Temecula, Murrieta, and Lake Elsinore.

According to the Southern California Earthquake Data Center (SCEDC), the fault has a slip rate of approximately 4 mm/year (0.16 inch/year), indicating gradual accumulation of tectonic strain. Though relatively quiet in recent decades, this slow deformation contributes to long-term seismic potential.

As the Elsinore Fault reaches Corona, it splits into two parts: the Chino Fault, which goes toward Chino Hills, and the Whittier Fault, which runs through or near areas like Whittier, La Habra Heights, Hacienda Heights, Rowland Heights, La Habra, Brea, and Yorba Linda.

According to Jones, an earthquake is plausible, and it would start on the Elsinore Fault and move onto the Whittier Fault. This would send powerful energy straight into the L.A. Basin, making it one of the more dangerous earthquake scenarios.

In a model developed by the U.S. Geological Survey, an M7.8 earthquake along the Elsinore-Whittier system could produce violent shaking across a wide region. Cities that could see serious damage include El Monte, Hacienda Heights, Rowland Heights, Pico Rivera, Whittier, La Habra, Brea, Yorba Linda, Placentia, Chino Hills, Corona, Lake Elsinore, Murrieta, and Temecula.

The Elsinore Fault has been relatively quiet historically. The most significant recorded event occurred on May 15, 1910, near Temescal Valley, with an estimated magnitude of 6.0. This earthquake caused minimal damage, primarily toppling chimneys in areas such as Corona, Temescal, and Wildomar.

The fault extends southeast into Mexico, connecting with the Laguna Salada Fault. On February 23, 1892, the Laguna Salada Fault experienced a significant earthquake, estimated between M7.1 and 7.3. This event caused damage in both northern Baja California and southern California.

It has an estimated recurrence interval of approximately 250 years for major rupture events, suggesting there is a potential for a significant future earthquake, although the exact timing remains uncertain.

Several cities like Torrance, Santa Monica, and West Hollywood have taken steps to strengthen their buildings against earthquakes, requiring retrofits to boost safety. But in Los Angeles, steel frame buildings are still not part of any mandatory retrofit program—a gap that’s sparked concern about how ready the city really is for the next big quake. Meanwhile, in the Inland Empire, many older brick buildings are especially at risk.

In recent years, only two earthquakes with magnitudes above 5 have occurred beneath Los Angeles and Orange Counties — M5.1 earthquake in 2014 near Brea and M5.4 event in 2008 near Chino Hills. The 2014 earthquake caused USD 2.5 million in damage, while the 2008 event resulted in minimal impact, according to regional seismic records.

California’s high earthquake risk comes from its location on the edge of a tectonic plate boundary. The Pacific plate—home to cities like San Diego, Los Angeles, and Santa Barbara—is slowly shifting northwest, while the North American plate—holding San Francisco, the Central Valley, and Big Bear Lake—moves in the opposite direction. This movement builds up stress over time, which is eventually released in earthquakes.

Advances in engineering, building codes, and early warning systems have significantly improved public safety and infrastructure resilience, especially in high-risk regions. While the potential for strong earthquakes exists, ongoing preparedness and mitigation efforts continue to reduce the likelihood of catastrophic outcomes.

¹ This little-known earthquake fault has been quiet. But it can unleash devastation across SoCal – Los Angeles Times – April 15, 2025

² M=4 Southern California earthquake highlights Elsinore Fault’s destructive potential – Temblor.net – January 25, 2018

³ Elsinore Fault Zone – SDEDC – Accessed on April 17, 2025

Reet Kaur

I’m a science journalist and researcher at The Watchers, contributing to the Epicenter edition, where I cover peer-reviewed scientific research and emerging discoveries across Earth and space sciences. With a background in astronomy and a passion for environmental science, I’ve worked in shark and coral conservation in Fiji, conducting reef and shark-behavior research, contributing to mangrove restoration, and earning PADI Open Water and Coral Reef Certifications. I bring a blend of scientific rigor and storytelling to illuminate the discoveries shaping our planet and beyond.

This author does not have any more posts.