Quake alert shakes many — too many?

New app sends warnings to areas nowhere near Tahoe temblor

Tens of thousands of Californians received earthquake alerts on their phones Thursday night around the times a series of quakes shook the Truckee area in Lake Tahoe. But not all those alerts went out to people in the area, with some people hundreds of miles away receiving the alerts despite feeling no shaking.

That is partly because the system that detects the earthquakes, called ShakeAlert, briefly overestimated the magnitude of the quake at 6.0 — which would have been felt as far away as the Bay Area — before correcting to the current estimate of a magnitude 4.7, according to Professor Richard Allen, director of the UC Berkeley Seismology Lab.

Allen said the system is based on hundreds of ground sensors throughout the state that pick up and estimate seismic activity, but that there are fewer sensors in the area near Thursday’s earthquakes than in other more seismically active parts of the state like the Bay

Area or Los Angeles. He said the system is about 70% installed with another 300 or so sensors expected to be placed into the ground to increase accuracy during the next two years.

“ShakeAlert determines the area where people are likely to feel shaking,” based on quake magnitude Allen said. He said the system initially overestimated but sent out a corrected alert within about one second.

“In this case we overestimated the magnitude by quite a lot,” Allen said.

The alerts go out automatically to people using Android devices who are likely to feel shaking, according to Brian Ferguson, deputy director for crisis communication and public affairs at the Governor’s Office of Emergency Services. An app for iPhone and Android users called MyShake created by by UC Berkeley’s seismology lab also notifies people of potential seismic activity he said, adding around 45,000 people got alerts through the app last night and Android alerts were still coming in.

“I think it was a success,” said Robert de Groot, the ShakeAlert national coordinator for communication, education and outreach.

Some social media users who said they were hundreds of miles away from the epicenter complained of receiving the startling alerts about a potential magnitude 6.0 earthquake but then feeling nothing. Ruby Chavez said in a message that she got the MyShake notification on her phone despite being located in the South Bay.

Ferguson said the MyShake and Android notifications are based on the data gathered from the ground sensors throughout the state that feed information into the ShakeAlert system. The apps also use smart phones to detect and study seismic activity but that is separate from the alert system.

He said the series of temblors Thursday night in the Tahoe area were the most widespread, if not the largest, since the system came online.

“We’ll learn from this and evolve and be more sophisticated the next time this happens,” Ferguson said, adding if there is a chance of an earthquake detected by the inground sensors it is better to send out an alert.

But why did some get the alert, while others in the same region did not?

“There are a lot of factors and it’s really hard to diagnose that just sort of on the fly,” de Groot said. But he does recommend that people in earthquakeprone areas download multiple alert products on their phones. “It’s better to have five alerts than no alerts,” he said. “So we really recommend people to have as many as possible.”

Ferguson also said that the early warning system is linked with infrastructure including BART and some firehouses in Menlo Park, among others, to automatically slow trains and open firehouse doors when an earthquake of a certain magnitude is detected. With the technology pushing alerts to people in a wide geographic area, it’s not clear if those features can be triggered automatically when there is no danger.

Ferguson said that to his knowledge none of them had been set off because of the Tahoe shakers.

The ShakeAlert system is still being tested on the West Coast. While the system itself is “up and running and working really well,” de Groot says the USGS is still working to build more seismic stations across Washington, Oregon and California and decrease alert delivery times. Better coverage of earthquake prone areas “leads to better detection and better characterization of the earthquake,” he said. He added that he expects construction of these stations to be completed around 2025.

He said that even though many people likely got an alert last night for an earthquake they didn’t feel, “the bottom line is the opportunity to practice that protective action is good, because the sooner you do it, the safer you’ll be.”