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California's Early Earthquake Warning System Worked Wednesday Night (For Some)

Polygons created by ShakeAlert, which denote different anticipated shaking intensities. Every MyShake user within the MMI 3 polygon should've received an earthquake early warning. (USGS)
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Just before waves from the 5.5 magnitude earthquake reached Los Angeles Wednesday night, people were warned that shaking was coming.

"I looked at my phone and I said to my husband, 'We have 30 seconds. There's a five-point-something earthquake coming,'" said Ginny Brideau who lives in downtown L.A. She, her husband, and their daughter used the time to brace themselves.

"Other times when there's been an earthquake, there's that moment of, 'Oh my gosh, what's happening,'" she said. "Instead, there was, 'The earthquake is coming. Let's get prepared.' And there it was!"

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California's earthquake early warning system seems to have worked as intended. When ShakeAlert's vast network of sensors picked up the first set of waves released by the earthquake near Ridgecrest, computers calculated the quake's size, and built a map of anticipated shaking intensity across California.

That information was then made available to ShakeAlert partners -- apps including California's MyShake, which then sent alerts to people within certain zones expected to receive the highest levels of shaking. Last night, that was supposed to include app users across all of L.A.

"This is the first big successful alert we've had with MyShake," said Angela Chung, a seismologist at the Berkeley Seismology lab and project scientist with ShakeAlert.

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The app was released last October, and according to Chung, notified roughly 20,000 people on Wednesday.

While it worked for some, it didn't for others, even those in the same neighborhood.

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For instance, I'm in Northridge, have the app installed and didn't receive a warning, while geophysicist Julian Lozos, who also lives in Northridge, did.

A very unscientific Twitter poll garnered more than thirty responses from a mishmash of people all over Southern California, all with various carriers and devices.

Some received notifications. Others didn't. No clear pattern presented itself.

Even Brideau, who has two phones -- a Samsung for work and an iPhone as her personal device, both with MyShake installed -- was only alerted on one of them.

"We don't know specifically the exact reason why some people didn't get it," said Robert-Michael de Groot, USGS ShakeAlert National Coordinator. "It can be a function of which cell phone provider you're working from ... It could be a function of the operating system. It could be a number of different things."

The MyShake team didn't provide clarification by publication time.

As for L.A.'s app, ShakeAlert LA, it's unclear whether it sent out notifications. The team didn't respond by publication time either.

But, as both Chung and De Groot told me, the early earthquake warning system is in its early stages and will continue to improve overtime.


We don't want to scare you, but the Big One is coming. We don't know when, but we know it'll be at least 44 times stronger than Northridge and 11 times stronger than the Ridgcrest quakes last year. To help you get prepared, we've compiled a handy reading list