'Shamrock Shake': 4.4 quake strikes near Westwood, no damage reports (updated)

Earthquake Tracker

A magnitude 4.4 earthquake struck Los Angeles early Monday morning, but there were no reports of major damage or injuries, officials said. 

The quake, which was swiftly downgraded from an initial magnitude of 4.7, hit a few miles northwest of Westwood at a depth of 8.5 kilometers, according to the U.S. Geological Survey.

Tweet from CHP

RELATED: More details on KPCC's Earthquake Tracker

"I probably would have slept through it if my husband hadn't woke me up. It was located over in the Santa Monica mountains between Westwood and Encino," said Lucy Jones of USGS, who lives in Pasadena.

RELATED: Debunking 8 common earthquake myths

"When we look at the shaking distribution, I would expect there might be a small pocket where things were thrown off a shelf in Encino, the very southern end of the valley or up in the hills above Westwood, but if anyone has structural damage, they should have fixed up their house before now," Jones said.

Janet Miller of Sherman Oaks woke up to the jolt: "I had a picture fall with some glass and a lamp and in my office — very funny — I have show pictures. I'm a director-choreographer. So the 'Sound of Music' nuns went flying."

Still, the Monday quake was the most significant to shake Los Angeles since the 5.5-magnitude Chino Hills quake in 2008, according to USGS seismologist Robert Graves.

Already several small aftershocks greater than 1.5 have been recorded, Graves said, speaking at a press conference at a Caltech/USGS press conference Monday morning, which was carried by local TV stations.

It's unclear along which fault the earthquake occurred, Graves later told KPCC.

"Really the only definitive way we can assign a particular fault to an earthquake is if the fault ruptures right up to the ground surface," said Graves, adding that this quake did not seem to do that.

He says unlike the 1994 Northridge earthquake, this one likely wasn't a blind thrust fault, where one tectonic plate is thrust over the other.

He instead described this morning's shake as what's called a strike slip fault, meaning the two plates mostly just slid past each other, grinding side by side. 

Graves said officials are still analyzing the data but added that the quake was typical for the area, with shaking felt throughout Los Angeles and very little damage anticipated.

He also noted that an “early warning system” in Pasadena worked.

"The system gave us a couple seconds of warning, which is kind of what we'd expect at this distance.  The magnitude was a little bit off, but it certainly worked in terms of notifying ahead of time before the shaking arrived," Graves said.

RELATED: VIDEO: News anchors dive for cover as quake shakes LA

About 5 percent of earthquakes are actually foreshocks followed by similar or larger quakes, Graves said, so it was possible that another quake could strike within a few hours.

L.A. Mayor Eric Garcetti sent a statement Monday morning reminding residents about the importance of earthquake preparedness:

Today's earthquake is a reminder that every L.A. family must be prepared with food, water and other essentials, as well as a plan. While it appears the greatest impact of this temblor was a rude awakening, we are executing our post-earthquake protocols to survey our neighborhoods and critical infrastructure.

The post-earthquake protocol involved sending personnel from all 106 fire stations into their local communities to survey the neighborhood and critical infrastructure such as hospitals and communications facilities, Garcetti said.

This story has been updated.