LA on earthquake alert as fault lines hit highest stress levels in history: study

Los Angeles could be edging closer to “the big one,” with new research finding earthquake stress has reached its highest levels in at least 1,000 years along two of California’s most dangerous fault systems.

The study, published June 3, used computer simulations to examine how stress has built up along three segments of the San Andreas and San Jacinto faults near the San Bernardino Mountains over the past millennium.

Researchers found that two of the three fault segments have reached, or exceeded, the highest stress levels seen during that time.

The findings don’t mean a major earthquake is imminent, but they reinforce what seismologists have warned for years: Southern California remains primed for a powerful quake.

“We have been lucky in California not to experience a large urban earthquake since 1994 on Northridge,” Ahmed Elbanna, director of the Statewide California Earthquake Center and professor of earth sciences and engineering at the University of Southern California told The Sacramento Bee.

“In order to release the stresses, the stress levels that we are talking about in this study, we need a magnitude 7 or larger earthquake,” Elbanna said.

A quake of that size would be more than 125 times stronger than last week’s magnitude 5.6 earthquake in Mendocino County, which triggered nearly 657,000 early-warning alerts through the MyShake app.

The tremor knocked out power to about 8,000 Pacific Gas & Electric customers, injured several people and caused thousands of dollars in damage after merchandise tumbled from store shelves.

According to the study, a magnitude 7 or larger earthquake could threaten nearly 24 million people across Southern California, including greater Los Angeles and the Inland Empire.

Even before the latest research, scientists agreed the region would eventually experience another major earthquake.

“The authors themselves, and the community, do not find the findings of the study surprising,” Elbanna said, adding that Southern California’s crust is “critically stressed and ready to rupture in a large-sized event. Whether that event would happen tomorrow, or in 10 years, that’s the part that we don’t know.”

Researchers reconstructed 1,000 years of earthquake history using radiocarbon-dated sediments, tree-ring records and historical accounts.

They also examined Cajon Pass in San Bernardino County, where the San Andreas and San Jacinto faults intersect.

Lead author Liliane Burkhard, a professor of space research and planetary science at the University of Bern in Switzerland, said the pass is more than a geological hotspot.

“It is a chokepoint for major highways, rail lines and energy infrastructure, so disruption there would have consequences well beyond the immediate shaking,” she told the Bee. “It could affect transportation and energy corridors that the broader region depends on.”

Despite the warning, experts emphasized that California’s strict building codes are designed to withstand major earthquakes.

“You might see cracks or have things falling down, but the structures themselves should not fail,” Angie Lux, a seismologist at the Berkeley Seismology Laboratory told the Bee.

Scientists still cannot predict exactly when the next major earthquake will strike, but Elbanna said continued investment in earthquake preparedness and warning technology remains critical.

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