Some Bay Area residents were promptly woken up by a ShakeAlert app notification 10 seconds before a 6.4-magnitude earthquake in Humboldt County early Tuesday morning.

At 2:34 a.m., emergency officials released an alert via the ShakeAlert system operated by the U.S. Geological Survey telling people to drop, cover and hold on for an earthquake that occurred about 8 miles offshore of Ferndale, a town more than 250 miles north of San Francisco.

The alert was sent to some 3 million people in Northern California, and the system successfully operated as emergency service crews hoped, said Mark Ghilarducci, director of the California Governor’s Office of Emergency Services.

A ShakeAlert push notification appears on a user’s smartphone screen in Chico seconds before Tuesday morning’s 6.4-magnitude earthquake near Fortuna in Humboldt County. (Image via @mikeseco/Twitter)

“I was really happy to have given individuals an opportunity to drop, cover and hold or get to a place of safety within that 10-second timeframe,” Ghilarducci said at a news conference later Tuesday.

The earthquake prompted about 80 aftershocks, the largest being a 4.6 quake centered in Rio Dell.

Ghilarducci said the region is not a stranger to sizable earthquakes, but the most recent shake has caused critical damage to homes and essential infrastructure like water, gas and power lines. About 40,000 people remained without electricity in the county as of Tuesday evening.

“We’re working closely with PG&E to get that power restored in the area and make sure they’ve got all the resources to be able to do that,” Ghilarducci said.

A nearly dozen-person team from Caltrans also identified damage on the Fernbridge on state Highway 211. Vehicle traffic is closed off except for emergency personnel as crews begin reconstruction work on the bridge.

“I’ve issued a $6 million emergency director’s order to the district and one director in that area to bring a contractor on board as quickly as possible,” said Tony Tavares, director of Caltrans.

At least two people were reported dead and 12 others injured. A Humboldt County sheriff’s official said the two fatalities involved elderly patients who failed to receive timely medical care. Most of the other injuries were caused by non-structural items falling in people’s homes, like bookshelves or TVs. Emergency officials recommend residents to remove or secure dangerous items that could fall over in the event of an earthquake.

The total damage assessment of the quake is yet to be determined and will likely be released in a few days, according to Ghilarducci.

“This is a one team, one fight effort. Local and state folks are working together to be able to help out the community there,” Ghilarducci said.

Cynthia Pridmore of the California Geological Survey said the earthquake was likely on the Gorda Plate, a complex offshore area that has had about 40 earthquakes reaching magnitudes of 6 and 7 over the last century.

“We have sent some scientists out in the field from the California Geological Survey — and likely there are other scientists out there as well — as well as engineers to get a reconnaissance feel of what kind of damage and features are out there,” Pridmore said at a news conference. “We will be sending more people out there if needed to document the characteristics of this earthquake.”