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New research suggests Central California has experienced bigger earthquakes than scientists thought

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A new report suggests the central section of the San Andreas Fault could be more prone to large earthquakes than previously thought.

Most of California’s big, destructive earthquakes have happened in Northern or Southern California, in places like San Francisco or Los Angeles. Meanwhile, Central California is thought to be at much lower risk and has been relatively free of large earthquakes in the past, barring a few events like the 1925 Santa Barbara earthquake.

But new research from a team of scientists across the country suggests that not only does the central section of the state have a history of larger earthquakes than we thought, but that there’s also potential for bigger ones in the future.

California’s infamous 800-mile-long San Andreas Fault has three main sections: the northern section, which produced the devastating 7.9-magnitude 1906 earthquake in San Francisco, the much-quieter central section, and the southern section which produced earthquakes like the deadly 1994 Northridge earthquake near Los Angeles.

This fault is widely expected to be building energy for another massive earthquake, commonly referred to as the “Big One.” Experts say the regions between San Francisco and Los Angeles, like the Central Valley and Coast, are most likely much safer from that potential event, though not completely.

The 1925 Santa Barbara earthquake destroyed much of the city's downtown.
Video Still From British Pathé
The 1925 Santa Barbara earthquake destroyed much of the city's downtown.

But the new study from a team of researchers including experts from Columbia University and Utah State found that the central San Andreas may not be as calm as we thought.

“It suggests bigger earthquakes — perhaps not as big as 1906, but definitely larger earthquakes," said Heather Savage, a professor at UC Santa Cruz’s Seismology Lab and one of the study’s coauthors.

Savage said the research team, led by lead author Genevieve Coffey, studied rocks drilled from about two miles underground to study their biomarkers — any organic material left behind in the rock that got heated and cooked during earthquakes that caused a lot of friction.

“Like a tree, or algae, or a leaf that dies and gets buried," Savage said.

Those biomarkers let the researchers calculate the degree of heating in the rock, which allows them to estimate how far the fault moved and how big past earthquakes could have been.

Savage said this led them to conclude that large, major earthquakes may have happened in Central California’s past, anywhere from a few hundred years ago to about three million years ago.

"We don’t always know if that’s the case, and we’re still actually refining the ages that we have in the paper right now," Savage said.

While large documented quakes in Central California’s past could mean bigger-than-anticipated quakes here in the future, Savage said a 1906-level event is unlikely — and that modern California building codes should protect against widespread damage.

"As Californians, we should always be prepared, and nothing about this study should overly alarm anyone," Savage said.

The research was recently published in the online journal Geology. More information is available online at climate.columbia.edu.

Benjamin Purper was News Director of KCBX from May of 2021 to September of 2023. He came from California’s Inland Empire, where he spent three years as a reporter and Morning Edition host at KVCR in San Bernardino. Dozens of his stories have aired on KQED’s California Report, and his work has broadcast on NPR's news magazines, as well. In addition to radio, Ben has worked as a newspaper reporter and freelance writer.
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