Early warning system not triggered ahead of California-Nevada earthquake: Here’s why

Bay Area

SAN FRANCISCO, Calif. (KRON) — Thursday’s magnitude-6 earthquake in the Antelope Valley triggered the U.S. Geological Survey’s Shake Alert early warning system, but USGS says a lack of ground sensors in eastern California resulted in inaccurate information being sent out.

“The outside edge of the wave front was picked up by clusters of stations in  more distance locations and created three separate earthquakes,” Doug Given, USGS Earthquake Early Warning Coordinator, said. “One in the Central Valley near Stockton and one in the Mammoth Lakes area and one near Mono Lake.

Because Shake Alert ID’d three smaller quakes instead of one big one, only 303,000 people in and around Mammoth Lakes and Stockton got the alert on their phones. 

“Had the system correctly characterized the magnitude-6 earthquake at the right location it would have alerted a much larger area than it did,” Given said.

As opposed to just Mammoth Lakes and Stockton, alerts should have gone out 350 kilometers in each direction from the epicenter. About as far west as Napa, as far north as stones landing. As far east as Winnemucca and Goldfield, Nevada and as far south as Fresno.

As the system improves in terms of science and software and station building out we expect the system will be more reliable with time. 

USGS says 70% of those ground sensors are in place mostly in major metropolitan areas. They say getting the remaining ones in place in more rural areas will take two to three years.

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