When a fierce 6.4 magnitude earthquake convulsed coastal Northern California on Tuesday morning, china flew from cabinets near the epicenter, and residents woke to find their power out and their floors blanketed in glass.
Hundreds of miles south in the Bay Area, bleary-eyed people were startled out of bed when a shrill alarm bleated from their cellphones, up to two minutes before the shaking started.
Some instantly took to Twitter after the alert from the MyShake early warning system with its three-note chime and a man’s computerized bellow: “Earthquake. Drop, cover, hold on. Shaking expected.” And some were irritated when they rushed to check their phones at 2:34 a.m. but did not feel the ground sway beneath them.
Nonetheless, many also said they were grateful for the technology.
It only took seconds for reports of the Ferndale earthquake to spread across Northern California, after 271,000 MyShake users heard their phones squawk, according to Richard Allen, director of the Berkeley Seismological Laboratory and leader of a team that developed the software.
Overall, more than 3 million people across California and Oregon received some kind of alert, officials with the U.S. Geological Survey said.
App users who had set their home base locations in the Bay Area and then traveled for the holidays got earthquake warnings in far-flung locations, including Miami and Mexico.
Roan Kattouw, a San Francisco resident visiting in-laws in Ohio, said he bolted upright when the siren-sound of MyShake woke him up at 5:30 a.m. Eastern time.
“I deleted the app, personally,” Kattouw said, adding that he might have been just as aggravated had he been home in San Francisco.
Allen encouraged people who do not want alerts for faraway earthquakes to use the app’s default setting, which tracks a phone’s current location, rather than its home.
“Earthquake early warning is never going to be perfect,” he said. “We very rapidly come up with our best estimate of the magnitude, and we send out a warning to anyone in the zone that would normally feel shaking. Usually it works well, which means we have a few seconds to protect ourselves in a devastating earthquake.”
Given the strength of the Ferndale temblor, which rocked areas of California’s northern coast for 20 seconds, the Bay Area remained conspicuously calm, surprising Allen and other seismologists. Though Allen would typically expect a more intense ripple through the Bay Area, he acknowledged that the rattling decreases the farther away people are from the site of the quake.
By contrast, many Bay Area residents felt a 3.6 magnitude temblor that struck El Cerrito early Saturday morning — knocking pictures from the fireplace mantel at a reporter’s home near the epicenter, for example — though the earthquake was not strong enough to trigger a MyShake alarm.
MyShake starts blaring only when tremors reach 4.5 magnitude or more, Allen said, a threshold the engineers set so that people won’t constantly receive alerts for small quakes jostling various parts of Northern California. Most people who have downloaded the app are hundreds of miles away from Ferndale in Humboldt County, where three plates join to form the Mendocino Triple Junction that ruptured Tuesday.
Jason Patton, an engineering geologist for the Department of Conservation’s California Geological Survey, calls this tectonic junction “the Triangle of Doom.”
“It’s the most seismically active part of California,” said Patton, who lives in the sand dunes west of Eureka. He noted that the area hasn’t been extensively studied because few people live there, which may also explain why it wasn’t saturated with cellphone alarms on Tuesday morning.
While most of the warnings reached people far away from the hard-hit areas of Ferndale, Arcata, Eureka and Rio Dell, the MyShake app “worked great from a technical standpoint,” Allen said, noting that the detector algorithms functioned just as they were designed. He said a handful of Bay Area residents detected light wobbling, indicating the earthquake’s sweep.
MyShake has enabled researchers at UC Berkeley and other laboratories to treat the earthquakes that jolt California as data for an ongoing research project. Phones equipped with the app that are plugged into power and are stationary will record the ground motion when a quake strikes, using the phone’s accelerometer as a tiny sensor.
These phones are akin to seismic instruments distributed throughout the urban environment. They log the waveforms from earthquakes and upload the reports to Berkeley Seismological Laboratory, presenting scientists with a clearer picture of how people experience earthquakes in a region where the ground often snaps.
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