A 4.2 magnitude earthquake struck the San Fernando Valley early Thursday morning, jolting some residents awake in the pre-dawn darkness and rattling nerves across the region.
The temblor hit at 4:29 a.m. between the 210 and 5 freeways, about 1 mile north of Pacoima, and two miles from the city of San Fernando, according to the U.S. Geological Survey. It initially registered as a 4.5 magnitude before being downgraded.
The quake was centered near the intersection of the 1971 Sylmar quake and the 1994 earthquake, where there are a number of fault zones nearby, according to Caltech seismologist Jennifer Andrews.
It was “widely felt” throughout the greater Los Angeles area, and as far away as Lake Forest and Rancho Cucamonga. The geological survey received some 15,000 responses on the agency’s “Did you feel it?” page in response to the temblor.
In terms of the intensity of the shaking, most of the responses were no higher than a five, meaning the quake wasn’t generally strong enough to even topple small objects off shelves, according to USGS seismologist Susan Hough.
“Typically in California, where things are fairly well built, you have to get up into the higher reaches of magnitude 5 before you see any real damage,” she said.
But one viewer, Koko Latchinian, shared a video with KTLA of some items that were knocked over when a large mirror fell at a home in San Fernando.
And another viewer in the south end of Simi Valley told KTLA the earthquake was strong enough to cause him to fall out of bed. He stated he was not injured.
Renowned seismologist Lucy Jones described the quake as “garden variety” for California.
By 11 a.m., at least 16 aftershocks had been recorded, with the largest measuring 3.8 and at least 10 registering over a 2.0 magnitude, seismologists said.
There’s about an approximately one in 10 chance that an earthquake of equal or larger magnitude will strike the area within the next month, according to Hough.
“The odds of something happening are, it’s more likely to happen soon after the initial 4.2, so the more time goes by, the more that probability drops. That one in 10 number sill be lower tomorrow and the day after,” she explained.
ShakeAlert sent out a tweet at 5:03 a.m. stating a message had been passed along.
Officials later said that notifications were sent out through two apps that service the region, QuakeAlert and MyShake.
The first alert was sent approximately 3.6 seconds after the shaking started, while the final alert was delivered nearly 13 seconds after the tremor, according to Robert de Groot, who is involved with the ShakeAlert Earthquake Early Warning System at USGS.
At a news conference, de Groot said about 10,000 alerts were delivered across Southern California through those apps.
“Really good results from this particular event,” he said.
But many people who have subscribed to ShakeAlertLA complained they did not receive an alert about the quake on their cellphones. USGS is still waiting on data from the city of L.A.’s earthquake early warning mobile app, according to de Groot.
Even though no major damage or injuries were reported, officials said seismic activity served as yet another reminder that Californians should be prepared for earthquakes.
“All of these earthquakes are always a reminder that this is California, earthquakes happen, and we need to stay mindful of that,” Hough said.