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South Napa Earthquake Woke Up Many, Fitness Trackers Reveal

a diagram of the percentage of people awakened by the earthquake.
Scientist at Jawbone look at the effects of the South Napa earthquake on people's sleep in several cities. (Image credit: Jawbone)

It might be possible to know how many people woke up during the South Napa Earthquake that struck 3:20 a.m. yesterday (Aug. 24) by looking at their fitness trackers.

The 6.0-magnitude earthquake that hit Northern California was the strongest to strike the region in 25 years. Data scientists at Jawbone, which makes the UP and UP24 fitness trackers, analyzed how the earthquake may have affected thousands of UP wearers in the Bay Area who track their sleep using the fitness devices, according to a statement from the company.

The results showed that 93 percent of UP wearers who were within 15 miles of the earthquake's epicenter — in the areas of Napa, Sonoma, Vallejo and Fairfield — suddenly woke up at 3:20 a.m. when the quake struck. [Photos: The Great San Francisco Earthquake]

Farther out, about 25 to 50 miles from the epicenter in San Francisco and Oakland, only 55 percent of UP wearers woke up, while the rest seem to have slept through the shaking. In Sacramento and San Jose, which are 50 to 75 miles from the epicenter, 25 percent of UP wearers woke up, according to Jawbone.

Even farther out, in Modesto, Santa Cruz and other places between 75 and 100 miles from the epicenter, almost no UP wearers were awakened by the earthquake, according to their fitness tracker data.

The Jawbone UP is a wrist-worn device that can track users' movements during sleep, and provides a record of the time they spent in bed, as well as the time spent in deep and light sleep. These records give users a ballpark estimate of their sleep quality and enable them to track their sleep patterns over time.

The device also tracks people's steps when they are walking, and that's how Jawbone scientists know people actually woke up, and were not simply being shaken during their sleep by the quake. "Steps look a lot different than earthquakes," Brian Wilt, Jawbone's senior data scientist, told Live Science in a tweet. "We have to filter [people's] motion in cars, trains, etc. all the time."

The Jawbone data also showed that it took people a long time to go back to sleep, especially in the areas that felt the shaking the strongest. In fact, 45 percent of UP wearers living less than 15 miles from the earthquake's epicenter stayed up the rest of the night, Eugene Mandel, from Jawbone's data science team, said. 

Email Bahar Gholipour. Follow Live Science @livescience, Facebook & Google+. Originally published on Live Science.

Bahar Gholipour
Bahar Gholipour is a staff reporter for Live Science covering neuroscience, odd medical cases and all things health. She holds a Master of Science degree in neuroscience from the École Normale Supérieure (ENS) in Paris, and has done graduate-level work in science journalism at the State University of New York at Stony Brook. She has worked as a research assistant at the Laboratoire de Neurosciences Cognitives at ENS.