A recent magnitude 5.2 earthquake in San Diego has revived fears among geologists and locals alike, bringing renewed attention to the Elsinore Fault, a little-known but potentially catastrophic fault line.
While frequently overshadowed by its infamous neighbour, the San Andreas Fault, the Elsinore Fault is emerging as a significant seismic concern. This lesser-known fault, which stretches over 100 miles from the US-Mexico border through San Diego and Riverside Counties and towards Los Angeles, has come to light as a result of the seismic that jolted the region earlier this week.
According to the California Institute of Technology, the Elsinore Fault is one of the major fault zones in Southern California, located just 15 miles from areas of San Diego County. Although it has been largely silent for decades, scientists believe that this quietness may be deceptive.
Dr. Lucy Jones, a well-known seismologist and expert on California earthquakes, stated that the fault is capable of producing a severe quake of up to magnitude 7.8.
“The Elsinore fault is one of the major risks in Southern California,” Dr. Jones said after Monday’s earthquake. “The last couple years, we’ve been having more felt-earthquakes than we had for several decades.”
Historically, earthquakes of magnitude 6.0 or more have occurred on the Elsinore Fault every 100 to 200 years, with the most recent large one reported in 1910.
In anticipation of such a situation, the US Geological Survey (USGS) has simulated what a large earthquake on the Elsinore Fault may look like – and the results are grim.
The simulation predicted widespread structural damage, intense shaking from San Diego to Los Angeles, and millions affected throughout Southern California. Cities such as Los Angeles, which has over 4 million population, will experience high Modified Mercalli Intensity (MMI) levels ranging from 7.5 to 9.0, threatening building foundations and causing fires, landslides, and power outages.
“The Elsinore is sort of a junior sister to the San Andreas,” Dr. Jones said. “As the San Andreas enters Southern California, it splinters into four major faults — the San Andreas, San Jacinto, Newport-Inglewood, and the Elsinore.”
Though earthquakes are less common along the Elsinore, scientists warn that when they do occur, the impact radius is vast, stretching into Los Angeles, Las Vegas, Santa Barbara, and even Fresno.
According to a 2017 USGS simulation, a magnitude 7.8 earthquake originating on the Elsinore Fault and extending into the nearby Whittier Fault would cause severe shaking throughout Los Angeles County, damage to thousands of buildings and bridges, minor to moderate damage in San Diego, light tremors as far as Las Vegas (approximately 300 miles away), and impacts felt by over 23 million people.
While San Diego may sustain moderate damage with MMIs ranging from 4.0 to 6.5, Los Angeles and nearby urban areas may face far more devastating effects, with fatalities, injuries, and financial losses expected to be significant.
Some experts believe that tectonic stress in Southern California, which was previously suppressed by major quakes such as the 1992 Landers (M7.3) and 1994 Northridge (M6.7) earthquakes, is resuming.
“The 1990s earthquakes depressed local tectonic stress for years,” Dr. Jones added. “But we’re starting to see that energy return — much like we did in the 1980s.”
If a quake of this magnitude strikes in the Elsinore or San Andreas systems, prior USGS models anticipate up to 1,800 deaths, more than 50,000 injuries, billions of dollars in infrastructure damage, and extensive disruption of transportation, water, and electrical systems.
Scientists are warning communities to remain prepared as the legacy of prior disasters, such as the 1906 San Francisco earthquake, which killed over 3,000 lives, looms large in California’s seismic history.
Despite its placid character, the Elsinore Fault is now firmly on earthquake specialists’ radar, providing as a reminder that the “Big One” may not strike where many expect.
“It’s not about if, but when,” Dr. Jones emphasised. “And we need to be ready for that when.”
