Earthquakes: LA has a bigger threat than the San Andreas fault

The recent earthquakes that have rocked California may be the result of a fault in southern California, considered even more dangerous than the San Andreas fault.

Los Angeles was rocked by a magnitude 4.4 earthquake just a week after a magnitude 5.2 earthquake struck near Bakersfield.

While none caused major damage, experts warned that Monday’s quake could have been associated with the Puente Hills thrust fault, which could one day trigger a huge earthquake in Los Angeles.

“All of these earthquakes are closely spaced in three dimensions, just below the main Puente Hills thrust (fault) plane,” said James Dolan, a professor of earth sciences at the University of Southern California. LA Times. “They are all associated with the same group of small events.

“But the key is that they are very small events. These are very small earthquakes that don’t necessarily mean anything in terms of the potential to be a harbinger of a future large-magnitude earthquake on the Puente Hills thrust.”

The Puente Hills Thrust Fault is a significant geological fault system located in Southern California that extends approximately 25 miles beneath the Los Angeles Basin, including areas such as downtown Los Angeles, Whittier, and the Puente Hills.

The Puente Hills thrust fault is a blind thrust fault that occurs when one part of the Earth’s crust is pushed up over another, usually due to compressional forces. The term “blind” indicates that the defect does not reach the surface, making it invisible at ground level and harder to detect without specialized equipment.

Monday’s earthquake struck at a depth of about 7.5 miles, along a fault strand that stretches only a few hundred meters. Other smaller earthquakes have recently occurred in the same area, with magnitude 3.4 and 2.8 quakes recorded in early June, followed by a 2.9 quake a few weeks later.

Earthquakes on the Puente Hills thrust fault could be particularly dangerous because the shaking would occur directly beneath Los Angeles’ surface infrastructure, potentially causing severe damage. The Puente Hills thrust fault is estimated to be capable of generating earthquakes with magnitudes up to 7.5.

The famous San Andreas Fault stretches about 750 miles from the Salton Sea in Southern California to Cape Mendocino in Northern California. It passes relatively close to Los Angeles, San Francisco and other major cities, but does not come as close to major population hubs as the Puente Hills thrust fault.

So while the San Andreas fault can generate stronger earthquakes—up to magnitudes of about 8.0 or even larger—the location of the Puente Hills thrust fault makes it a major hazard.

“It’s a reminder that this is actually our most dangerous mistake,” said earthquake expert Lucy Jones. LA Times.

The USGS estimated that a major earthquake of magnitude 7.8 on the San Andreas fault could kill about 1,800 people, while a magnitude 7.5 earthquake on the Puente Hills fault could kill up to 18,000 and cost up to 252 billions of dollars.

The Puente Hills fault has not had a major earthquake in recorded history, although geologists believe it may have one every few thousand years. The San Andreas Fault, on the other hand, has a major earthquake once every few hundred years, the most recent occurring in 1857, which is believed to have a magnitude of 7.8.

However, even smaller earthquakes on the Puente Hills fault can be very damaging: a magnitude 5.9 earthquake on the fault in 1987 killed eight people and caused more than $350 million in damage.

“People really need to be prepared for a very, very large earthquake, or earthquakes, in the future in LA,” Dolan said. “It will happen. We don’t know when. We don’t know exactly which fault will generate those earthquakes, but they will happen.”

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