Tiny Southern California fault poses a bigger threat than San Andreas

While California’s 750-mile-long San Andreas Fault is notorious, experts believe a smaller fault line possesses a greater threat to lives and property in the southern part of the state.

According to the U.S. Geological Survey, Monday’s 4.4 magnitude earthquake near Los Angeles’ Highland Park neighborhood occurred along the Puente Hills Fault , also known as the Puente Hills Thrust Fault system.

This 25-mile-long fault runs from the Glendale/Pasadena area to Puente Hills and has been extremely active in recent months. The same fault was the site of a magnitude 3.4 quake on June 2 and a magnitude 2.8 on June 4.

A 2.9 magnitude quake also shook the area on June 24.

“That fault runs right through Los Angeles, which is why we need to be concerned about it,” said Dr. Lucy Jones, a Caltech researcher and California’s preeminent seismologist. “It has the potential for a very large earthquake. It has been modeled up to magnitude seven and a half.”

For comparison, 1994’s Northridge Quake , which killed 57 people and caused tens of billions of dollars in damage, was a magnitude 6.7.

The USGS estimates that if the Puente Hills Fault were to produce a “full rupture,” damage could top $252 billion, hundreds of thousands of people would be displaced from their homes, but more alarming of all, 3,000 to 18,000 people could die .

“[It would be] a higher death toll than we would see from the San Andreas because it is so much closer to people,” said Jones.

This doesn’t downplay the threat of the notorious San Andreas Fault, which transects the San Francisco Bay Area and produced 1989’s Loma Prieta quake (magnitude 6.9) and The Great 1906 San Francisco Earthquake (magnitude 7.8).

In Southern California, however, the San Andreas Fault runs largely through remote mountains and deserts and terminates at the Salton Sea – far away from densely populated areas.

After several decades of below-average seismic activity in Southern California, Jones says 2024 has been extremely active , with 13 quakes measuring 4.0 or greater thus far. This trend, she says, is likely to continue.

She hopes the recent temblors will serve as a reminder that a powerful quake could strike at any time and that residents need to be on alert.

“Being prepared doesn’t just mean having supplies; having water is important, but talking with your friends and family about it and having a plan together is probably more important than anything else,” Jones said.

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