A magnitude 4.7 earthquake just north of Malibu rattled Southern California on Thursday, and was followed by a magnitude 3.4 aftershock about an hour later.
The temblor struck at 7:28 a.m. and was felt across the region. No damage was reported. There have been at least three aftershocks in the magnitude 2 range. At 8:40 a.m., a magnitude 3.4 aftershock occurred.
The earthquake epicenter was closest to the Malibu fault, said seismologist Lucy Jones, a Caltech research associate. Initial analysis suggests the quake had a 40% chance of being associated with the Malibu fault and a 46% chance of being associating with the Anacapa fault.
Earthquakes of this magnitude rupture only a relatively small section of fault, perhaps a matter of 100 yards or a few hundred yards. As such, these modest earthquakes can often happen on small faults that are not associated with faults that are much larger and mapped at the Earth’s surface.
“Light” shaking, as defined by the Modified Mercalli Intensity Scale, was felt in Malibu, Thousand Oaks, Agoura Hills and Calabasas. Light shaking disturbs dishes, windows and doors, makes cracking sounds in walls, and can feel like a heavy truck has struck a building.
In Thousand Oaks, one resident reported the shaking lasting a few seconds, while another resident elsewhere felt about 12 seconds of rattling.
“Weak” shaking was felt over most of the Los Angeles metropolitan region, including downtown L.A.; Santa Monica; Long Beach; the San Fernando, San Gabriel and Antelope valleys; Orange County and the Inland Empire. There were crowdsourcing reports indicating shaking was felt as far away as San Diego and Bakersfield.
People along the L.A. County coast felt notable shaking. Some people in Redondo Beach and Long Beach felt shaking for a 10 seconds. In Redondo Beach, a person felt the shaking begin small and then intensify, but nothing fell from shelves. In Long Beach, a resident felt a shake and a roll.
Near the Los Angeles International Airport, an apartment building in El Segundo shook and curtains swayed.
Emil’s Bake House is a favored early morning stop of commuters streaming from the 101 Freeway to Malibu via Kanan Road in Agoura Hills.
Julius Speck was at the counter serving customers lattes, scones and vegetable juice when the windows and display cases violently rattled.
“I thought somebody dropped something in the back,” Speck said, pointing to the kitchen. “I was confused.”
The shaking lasted only a few seconds and Speck said he took a deep breath and asked the next customer what they’d like to order.
There have been more noticeably felt earthquakes recently in highly populated areas of Southern California. But that fact doesn’t help predict whether a larger, destructive earthquake is expected to occur sooner than later, earthquake experts said.
Over the last 65 years, Jones said, there were an average of eight to 10 independent sequences of earthquakes with at least one magnitude 4 earthquake or greater. In some years, there’s just only one or two of those earthquakes; the highest number was 13 of those earthquakes, in 1988. Thursday’s earthquake is the 14th earthquake of magnitude 4 and above in Southern California so far this year, Jones said.
“So yes, this is a more active year than we’ve had in the past,” Jones said. But, she said, “we can’t quite say yet that whether or not that it is actually statistically significant to be seeing this.”
Another earthquake in Malibu, a magnitude 4.6, was felt on Feb. 9. That earthquake’s epicenter was about six miles to the southwest of Thursday’s earthquake.
Another cluster of earthquakes has been reported over the summer in the neighborhood of El Sereno, on Los Angeles’ Eastside, which occurred on the Puente Hills thrust fault system. The most recent was a magnitude 4.4 earthquake that occurred on Aug. 12. They were preceded by a pair of earthquakes in early June — a magnitude 3.4 on June 2 and a magnitude 2.8 on June 4, and a magnitude 2.9 earthquake in the same area on June 24.
The Puente Hills thrust fault system is the same overall fault network that produced the 1987 Whittier Narrows magnitude 5.9 earthquake — which killed eight people and caused some $358 million in damage. The Puente Hills thrust fault system is capable of producing a magnitude 7.5 earthquake, which runs under highly populated areas of L.A. and Orange counties and could kill 3,000 to 18,000 people.
Thursday’s earthquake moved in a horizontal, side-to-side motion, also known as “strike-slip motion,” Jones said. The other type of movement that can be felt in other earthquakes in Southern California are upward motions on a dipping fault.
Some residents were alerted by the state’s earthquake early warning system. In Koreatown, residents got about two seconds of warning before shaking arrived. A free earthquake early warning system app, MyShake, can be downloaded on the iOS and Google Play app stores.
On the C Line (formerly the Green Line) train heading west toward the Crenshaw station, cars erupted in beeping cellphone alarms as phones lit up with warnings of an earthquake. Passengers reached for their phones or looked around in alarm, but the train sped forward, swaying as usual. Despite the instructions on their phones, no one dropped to the floor or sought cover under their seats. Noticeable shaking from an earthquake was not noticeable on the train, which sways as it went down the tracks.
The Los Angeles Fire Department, as well as officials with Ventura County, reported no damage. The L.A. County Fire Department received no calls, nor responded to any calls for emergency, regarding the earthquake.
The quake was centered in the Malibu Hills off Kanan Dume Road around Ramirez Canyon.
Times staff writers Luke Money, Iliana Limon Romero, Ruben Vives, Richard Winton and Jon Healey contributed to this report.
