Mini Earthquakes Rock SoCal Every Three Minutes, Science Says

SoCal experiences thousands of earthquakes annually, scientists have found.
••• CHRIS DELMAS/AFP/GettyImages

California's no stranger to earthquakes – that's not news. But nearly 2 million tiny earthquakes over the course of a decade in Southern California alone? That is.

A study published earlier this month in Science Magazine reported evidence of 1.81 million tiny earthquakes over a 10-year period, thanks to new earthquake detection technology. That's 10 times the number of earthquakes scientists had previously detected in that time period.

Challenges to Earthquake Detection

It's "notoriously difficult" to detect small earthquakes, according to reporting from NPR. Earthquake sensors cover seismically active areas all over the country, and might register strong winds, passing cars or ocean movement as minor earthquakes. This poses challenges to scientists who rely on earthquake data to explore and understand what triggers the most intense, destructive quakes.

The team responsible for this recent study, however, claims to have found an accurate method of detecting tiny earthquakes. These scientists used a powerful collection of computer processors to analyze earthquake sensor data collected from about 400 seismic sensors between 2008 and 2017.

A group of 200 Caltech-based graphics processors spent tens of thousands of hours searching through the seismic data to pinpoint potential quakes. Other computers then spent hundreds of thousands of additional hours wrapping up the analysis. Overall, the analysis took about three years.

The result: Where scientists had already detected about 180,000 quakes in Southern California between 2008 and 2017, new analysis methods revealed 10 times that number.

Why Earthquakes Happen

An earthquake occurs every three minutes on average in Southern California, according to the study. Daniel Trugman, Los Alamos National Laboratory scientist and study author, said it can be tough to detect most of these quakes without a sensor.

"You don't feel them happening all the time," Trugman told NPR. "But they're happening all the time."

In fact, most of the earthquakes detected in this study measured below zero in magnitude. Still, they count, and they can help scientists understand more about larger earthquakes and when they might strike. Study co-author and Caltech seismologist Zachary Ross said accurate observations can help researchers predict when and where quakes might hit, and understand the physics behind larger tremors.

"We're starting to complete the story about the interaction between these events," Ross told Science News Magazine.

Emily Brodsky, a UC Santa Cruz seismologist, added that the work of Trugman and Ross and their team can help scientists understand the impact of human activity on earthquakes, as well.

"Arguments for whether or not something is human-induced revolve around timing and location," Brodsky told Science News. "The things is, very often there’s a delay, so that timing becomes ambiguous."

Learning more about these potentially continuous earthquakes could be a real game-changer.

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