Get an earthquake alert in Northern California? Here's why ShakeAlert targeted you
SACRAMENTO - Thousands of Northern Californians were notified of the Isleton earthquake by a loud noise and alert on their phones Wednesday. That alert was sent out by the United States Geological Survey (USGS) and its partners to notify you before the shaking – but how does it work?
A 4.2-magnitude earthquake hit Northern California Wednesday morning in an area about 2.5 miles south/southwest of the city of Isleton in Sacramento County.
The alert on your phones was sent through ShakeAlert, an early earthquake alert tool to let you know to prepare.
"When time is an important thing, every second matters with earthquake early warning, and so we needed to get something moving as quickly as possible," said Robert de Groot, a USGS Lead ShakeAlert Operations Team member.
According to the USGS, the earthquake struck at 9:29 a.m. Pacific Time, and was initially reported as measuring 5.7. It was then downgraded to 4.1, then back up to 4.2. USGS says that the magnitude reading can change over time, depending on how close the sensor is to the quake's epicenter.
"The ShakeAlert system really has a delicate balance between speed and accuracy, and every earthquake teaches us something new," de Groot said. "We're constantly improving, but the idea is to really prioritize human safety."
He said ShakeAlert will only notify you when a quake is 4.5-magnitude or larger. It targets urban areas, areas with large populations and also prioritizes known earthquake sources like the San Andreas, Hayward and Garlock faults.
However, with around 50 earthquakes recorded every day in California, no one is susceptible to feeling their impacts.
"People who could feel shaking, that's like a heavy truck passing by your house – that kind of vibration or greater. Those people are targeted to get alerts for that shaking," de Groot said.
The USGS has over 1,600 seismic stations in their network to monitor each fault line – from California to Oregon to Washington – by a wide net. When sensors at these stations feel the earth moving, that information gets sent out to the USGS processing center before they alert those who fall within the ripple of the quake.
"You don't know what areas are going to get shaken for every earthquake, but what we do in those just a few seconds of calculation is we figure out how big that event is going to be, what the magnitude of the earthquake is and then we also estimate the shaking around that epicenter so then we can tell our alert delivery providers you need to be alerting people in these areas," de Groot said.
Alerts can come through the Wireless Emergency Alert system, which sends text-message alerts similar to Amber Alerts sent to cellphone users. Some alerts may also come through earthquake alert apps like MyShake.
De Groot said that with each alert, it's important to take action and find a safe place.
"For us, the most important part of the messaging is for people to take that protective action if they feel shaking or if they get an alert, that protective action is drop, cover and hold on," de Groot said. "Earthquakes are going to continue to happen and its just a matter of us becoming more prepared and adding these wonderful tools like shake alert to our toolbox."
The Isleton quake comes just one day ahead of the planned Great California Shake Out drill to raise awareness about earthquake safety.
The drill Thursday will send out a similar alert as the ShakeAlert to people's smartphones but will say it is a drill.
The Shake Out drill hopes to encourage people and communities to update emergency preparedness plans and supplies and secure their space in the event of an earthquake.
The drill is expected to happen at 10:19 a.m. Thursday, October 19. To learn more and to take part click here.
