Earthquake rattles Northern California near Sacramento, triggering ShakeAlert. Here’s what we know

A small earthquake rattled the Sacramento-San Joaquin River Delta region of Northern California on Wednesday morning, prompting a widespread early warning and shaking residents near Isleton but apparently causing no damage.

The 4.2-magnitude temblor struck 2½ miles south-southwest of Isleton, a tiny Sacramento County city along the river, according to the U.S. Geological Survey. The epicenter was located near Jackson Slough Road and was 31 miles south of Sacramento.

Bob de Groot, a spokesman for the USGS, said the quake was centered on Brannan Island and ran through the Midland Fault at a depth of 6.7 miles.

“It was right on the fault,” de Groot said seismologists reported. “It wasn’t that big of an earthquake, but some may have felt a jitter.”

He said seismologists were reviewing the quake to fully understand what happened and had revised the magnitude from 4.7 to 4.1 to 4.2, but those who felt it the most were likely either close to the epicenter or on landfill or other soft soils.

“There was no damage, just normal right now,” said Thirak Chiv, owner of the Rio Vista Bakery and Grill, where the shaking was felt for five of six seconds. “It did shake a lot, but OK now so far.

“I don’t see anything damaged.”

Martha Esch, owner of the Lockeport Grill and Fountain, said she was sitting in her van at the B & W Resort Marina in Isleton when the quake hit.

“I was sitting in my van, no one around me and I thought that someone had bashed into the back of my van,” she said. “It shook back and forth several times.

“I got out of my van and looked around and there was no one there. And then the young woman came out of the snack bar looking really scared and said, ‘Oh, my God.’

“I have never felt an earthquake in the Delta in the 32 years I’ve lived here. It was exciting, especially since no one bashed into the back of my van. I hate to say it but it was fun.”

No reports of damage in Sacramento County

The Sacramento County Office of Emergency Services says were no reports of damage in the area, but officials are working to assess levees in the area.

Matt Robinson, a spokesman for Sacramento County OES, said road crews doing general work in the area have not seen any damage, and that OES was working with a patchwork of reclamation districts to check the levees that shake through the area.

Chelsea Davis, 22, was working the snack bar at the B & W Resort when she felt the quake.

“I’ve never felt anything like that before,” she said. “Usually, whenever an earthquake has hit we’re in the outer part of it.

“I feel like this was the first earthquake I’ve ever experienced like this.”

Davis said there was no apparent damage, although some fliers tacked to the wall fluttered to the floor.

“We’re in an older building so it was shaking super crazy,” she said.

Davis initially thought somebody was breaking into the store before she realized it was an earthquake when she saw the tackle moving.

“I was by myself,” Davis said, adding that she initially froze until a woman came in to get her out of the building. “She was such a sweetheart.”

‘Very short earthquake’ near epicenter

Stacy Wallace, the principal at Isleton Elementary School, said the quake triggered a warning for the school’s 210 students to take cover, and then evacuate.

“We had school in session,” Wallace said. “It wasn’t very long, it was a very short earthquake.

“As soon as we heard we got on the loudspeaker and said to stop, drop and cover, and then we had the kids evacuate as soon as it was done. We checked the building to make sure it was safe and as soon as we were sure we had them come back in.”

Wallace said the school had had a bus safety and evacuation drill earlier in the morning and that the students were well prepared.

“We do a lot of safety procedures, so they were pretty well practiced on their evacuation routes,” she said. “They did so well. They did really good.”

Wallace, who has been at the school for five years, said it was the first quake to hit during school sessions.

“This is the first one I’ve felt since I’ve been working here,” she said. “I know there’s been a couple at nighttime, but this is the first in school hours.”

Wallace added that there was no panic among the students during the event.

“Right now, they’re discussing their feelings and making sure that they are feeling supported and safe,” she said.

ShakeAlert shared widely in California

A ShakeAlert was triggered for just before 9:30 a.m. According to de Groot, officials are still crunching the numbers on how many messages were delivered through various partners, but roughly 400,000 received the notification via the MyShake app, which was developed by UC Berkeley.

De Groot said that once you factor in Google and mobile phone provider alerts, the number of notifications delivered were likely to be “very high,” he said. Alerts were sent not just to Sacramento and San Joaquin but to a number of Bay Area counties to the west.

Weak and light shaking was self-reported through the USGS’ website. By 10 a.m., more than 1,100 people said they had felt little to no shaking in parts of Placer, Sacramento, San Joaquin, Alameda, Contra Costa, Napa, Marin, San Francisco and San Mateo counties, according to the USGS.

Earthquakes are uncommon but not unusual for the Delta, which has seen more than 100 earthquakes in the upper portions of the Sacramento-San Joaquin system since 1965, though most were magnitude 3 or less.

Besides Wednesday’s quake, there have been only three other events in the past 60 years that were greater than magnitude 4.

The largest was a magnitude-4.9 temblor that struck around the Antioch area on Sept. 10, 1965.

According to noted seismologist Dr. Lucy Jones of Caltech in Pasadena, the Midland Fault where the quake originated is a notable northwest-striking fault, among a system of rifts that “bound the western Side of the Central Valley, pushing up Mount Diablo.”

She said one of the notable quakes the fault system produced was the Coalinga earthquake of May 2, 1983, which had a magnitude of 6.2 and was felt across the Central Valley and as far south as Los Angeles. That quake caused more than $10 million in property damage and injured 94 people.