Northern California 5.6 magnitude earthquake prompts ShakeAlerts for over 1 million people
More than a million people across Northern California, and some as far south as Modesto, received an earthquake alert Wednesday morning after a magnitude 5.6 earthquake struck in Mendocino County.
The earthquake hit around 8:10 a.m. in a remote area between Willits and Ukiah. While many people were surprised to see the warning pop up on their phones, especially those living hundreds of miles from the epicenter, officials say the ShakeAlert system is designed to err on the side of caution.
Within seconds of the earthquake, alerts were sent across Northern California. The process begins the moment the U.S. Geological Survey's network of seismometers detects an earthquake. Within just a few seconds, the system calculates three key pieces of information: where the earthquake occurred, its magnitude and how strongly the shaking is expected to be.
That information is then sent to ShakeAlert delivery partners, including the MyShake app, FEMA's Wireless Emergency Alerts system and the built-in emergency alert systems on Apple and Android devices.
Officials say the system prioritizes public safety by sending alerts to areas that could experience shaking, even if some people ultimately never feel it.
"The MyShake alert has access to ShakeAlert data, and what happens is they take that data and they use that to decide where they're going to send their alerts," said Robert de Groot, ShakeAlert operations team lead. "People in places like San Jose and Modesto probably got alerts from MyShake because that's the level that MyShake uses."
Another factor that contributed to the alert was the earthquake's depth.
The earthquake measured magnitude 5.6 and occurred at a depth of about five miles, which is considered shallow. Officials say shallow earthquakes can produce stronger shaking at the surface, increasing the potential impact for communities near the epicenter.
