But after all was said and done, most of us didn't feel a thing. So, what exactly happened? ABC7 News spoke with the U.S. Geological Survey to better understand how the system works.
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"One of the critical pieces of information with any earthquake is to know where it's located," said Robert de Groot, USGS ShakeAlert national coordinator. "When you know about where the earthquake is located, then you can get a sense of how the region around it is going to shake."
In this case, the system, which uses underground sensors to detect an earthquake, actually misread where the quake was located because there was only one station in the area. As a result, the quake ended up being closer to Truckee and turned out to only be a 4.7 on the scale. Some Bay Area residents were notified to take cover because the system thought the quake would be bigger.
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Despite the miscalculation, earthquake geologists say it's a good thing the system worked, and that the data will get even better as more sensors are installed throughout the state over the next four years.
"Those 10 or 20 seconds may save lives," said Kimberly Blisniuk, an earthquake expert and geology professor at San Jose State University. "What I think is great about this is that even though some people think that the system didn't work, it actually really did."
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There are two mobile apps that are powered by ShakeAlert. One of them is the MyShake app that was developed by U-C Berkeley and is sponsored by Cal OES. The other is QuakeAlertUSA. ShakeAlert also provides warnings to Google, which has an earthquake alert feature on devices using the Android operating system. Another way to receive warnings is if you have wireless emergency alerts enabled on your smartphone device.
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"I want people to think of it as a tool in their toolbox of earthquake preparedness," said de Groot.