More than 1,200 shallow earthquakes detected in southern California could lead to the Big One

Los Angeles could be at risk for a major earthquake, a study suggests.

Scientists at the California Institute of Technology (Caltech) have detected more than 1,200 shallow quakes in the past eight months.

These shallow quakes were detected about a mile below the surface, which can build up and create pathways for larger surface fractures.

The team studied Long Beach and Seal Beach, two LA suburbs along the Newport-Inglewood fault line.

Previous studies have suggested that this fault is capable of a magnitude 7.4 earthquake, which has “an energy equivalent to about 32 Hiroshima atomic bombs.”

Shallow earthquakes can feel like “a bomb right under a city,” Susan Hough, a U.S. Geological Survey seismologist, told the AP.

While the name doesn’t sound threatening, shallow earthquakes can pile up to create more pathways for intense earthquakes to rip at the surface.

The shallow quakes were previously undetected by the regional seismic network due to urban ‘noise’ from ships, reconnaissance equipment and other sonar technologies.

But through research in the evenings, when noise levels are low, the team was able to identify 1,262 events.

The Newport-Inglewood Fault extends 47 miles from Culver City southeast to Newport Beach, where the fault runs east-southeast into the Pacific Ocean.

And it was first identified after a magnitude 4.9 earthquake on June 21, 1920 near Inglewood, California.

The researchers said their findings “therefore, the high-risk zone at the surface may be much wider than the Alquist-Priolo zone indicates.”

Alquist-Priolo zones are regulated zones around the surface tracks of active faults in California.

Wherever an active fault is present, a structure for human habitation cannot be placed above the fault and must be a minimum distance from the fault – about 50 feet.

The researchers detected the shallow quakes using three dense seismic nodes temporarily placed in the Long Beach-Seal Beach area.

The team collected data between 9 p.m. and 5 a.m. PST in hopes of filtering out the noise from the environment, which proved successful.

The large number was expected, Yang said.

“The surprising aspect is the relative number of shallow events,” he continued.

Shallow earthquakes are caused by stresses on the fault that slowly increase in response to the slow movement of tectonic plates, with sliding onset as these stresses exceed static friction.

The investigation also revealed new errors between the Los Alamitos Fault and the Newport-Inglewood Fault and north of the Garden Grove Fault.

Yang said there was no evidence that the small shallow earthquakes detected in their study were caused by oil and gas operations.

The researchers said other faults in Southern California could be examined for these very shallow earthquakes to better characterize seismic hazards.

“The full-length Newport-Inglewood fault, as well as the entire Los Angeles watershed, could benefit from such studies,” Yang said.

“This would help to see if there are faults that have not been detected with the permanent seismic network or geological maps.”

While this study focuses on the Los Angeles area, a report from the United States Geological Survey (USGS) released this month, suggests the Bay Area is overdue for an earthquake measuring up to 6.7 on the Richter scale — and it could strike in 2030.

Alameda residents may stand in the way of the devastating event.

The small town was once a peninsula, connected to Oakland by a small landmass that was dredged over 100 years ago to extend a strait.

Speaking to a Bay Area newspaper, the director of earthquake science for USGS said the city is at risk of collapse when an earthquake finally hits — with Alameda poised to bear the brunt of the disaster.

“With stuffing, it’s kind of like a house of cards,” Christine Goulet of the USGS told me Mercury News Alameda’s earthquake readiness, saying citizens could see their community collapse before 2030 if nothing is done.

Goulet has a Ph.D. in civil engineering from UCLA, and said most of the six-mile-wide landmass is at risk of liquefaction — a phenomenon that occurs under severe shaking that causes water-logged soil to lose its strength and behave like a liquid.

She went on to warn that the wet wetlands pumped from the bottom of San Francisco Bay in the early 1900s are likely not properly tamped, leading to more cause for concern.

She said of the process, “What happens is they dredge material from the nearby sea or bay, which has a mix of clay and silt, and then they just put that in without compacting it properly.”