Southern California experiences an earthquake every three minutes, a new study finds

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The San Andreas Fault system, which stretches more than 800 miles in California, causes a powerful earthquake about every 150 years, according to the U.S. Geological Survey.

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Southern California gets a lot more action than we thought.

In a new study, researchers from the California Institute of Technology and University of California, San Diego have uncovered nearly two million previously unidentified tiny earthquakes that happened between 2008 and 2017. That translates to roughly 495 earthquakes a day in Southern California, or an earthquake about every three minutes.

An average person walking along the street wouldn’t notice these tiny temblors, which range in magnitude between -2.0 and 1.7.

Generally, people feel earthquakes of magnitudes higher than 3.0, according to the US Geological Survey.

Using larger earthquakes to find smaller ones

Even researchers who study earthquakes had a difficult time detecting these “hidden” earthquakes.

Background noise, such as shaking from automobile traffic or building construction, appears in seismic data and can mask signs of the smaller earthquakes.

To detect these elusive quakes, the scientists used a technique called template matching. From seismic data of already known earthquakes, they identified patterns as to what an earthquake’s signal should look like. Using this information, the researchers then scanned records from seismometers to find the tiny earthquakes.

Scientists now have a lot of data to learn from

The expanded earthquake data will help scientists understand how swarms of earthquakes evolve and previously unknown temblors that precede major earthquakes.

“Seismicity along one fault affects faults and quakes around it, and this newly fleshed-out picture of seismicity in Southern California will give us new insights into how that works,” Egill Hauksson, who worked on the study, said in a statement.

Marine Denolle, a seismologist at Harvard University who was not involved in the study, said she is excited about the future studies that this newfound data will generate.

“This is the biggest earthquake catalog ever,” Denolle told CNN. “This will help us find where earthquakes come from, and they can highlight new fault systems that we could not see before and reveal new tectonics that we were not aware of before.”

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