4.4-magnitude earthquake jolts Los Angeles: "This one easily could have broken some windows"

A 4.4-magnitude earthquake struck about 2.5 miles south of the Los Angeles neighborhood of Highland Park Monday, according to the U.S. Geological Survey.

It was reported at about 12:20 p.m. and felt throughout L.A. County in areas including Pasadena and Studio City. USGS initially reported the earthquake as a 4.6-magnitude temblor, later updating it to a 4.4 magnitude. There was another quake in the area in June, which had an epicenter in South Pasadena and was felt in areas stretching from Los Feliz to Long Beach.

Seismologist Dr. Lucy Jones said Monday's earthquake was in "essentially the same location" as the one in June. 

Los Angeles goes into earthquake mode

The Los Angeles Fire Department sent crews to check for potential damage to buildings. All 106 LAFD fire stations take part in the damage inspections performed as the city goes into earthquake mode.

At about 1 p.m., LAFD spokeswoman Margaret Stewart said the department was nearly done with those inspections, which also involve air and marine efforts, and no damage had been reported. She said she felt the quake at the LAFD headquarters.

"We felt it immediately," Stewart said.

According to Jones, there was likely so many reports about the earthquake since the epicenter was in a densely populated area of Los Angeles.    

"There's a lot of people on top of this earthquake," Jones said. "Fundamentally, if you know the other earthquakes you've been feeling and saying, 'I don't usually feel a 4 [magnitude] or smaller than a four, that's because you were farther away."

• Read More: What you need to do during and after an earthquake

LA Metro said earlier it was slowing down trains so that the tracks across the countywide transit system can be checked for damage but later said it was resuming regular service as no damage was found. 

South Pasadena Police Chief Brian Solinsky said around 1:10 p.m. that there had been no reports of injuries or damage. But he said the intensity of the shaking could have left some slight damage, explaining that the retrofitting of buildings may be partially why the city's infrastructure held up so well.

"This one easily could have broken some windows," Solinsky said.

At Pasadena City Hall, water gushed out of a broken pipe while firefighters looked through the building. Authorities have not said whether that was caused by the quake.

Seismologists at The California Institute of Technology, Caltech, said they felt shaking at the Pasadena campus. 

Last week, a 5.2-magnitude earthquake near Bakersfield rattled the Southern California region, with shaking felt throughout parts of Kern, Ventura and Los Angeles counties. 

In the following two days, there were more than 400 tremors within 10 miles of the quake's epicenter, which USC seismologist John Vidale said could all be considered aftershocks since that area doesn't usually have much seismic activity.

What fault was the earthquake on?  

Jones said there have been other earthquakes on the same fault as Monday's quake.

"This area has a network of varied faults, so it's not something that shows up on the same surface," Jones said. "The same network was involved in the 1987 Whittier Narrows quake, but exactly whether it's the same strand, because it's complicated and at depth, we'll never be able to say. But it is the same system as the Whittier Narrows."

That earthquake struck the southern San Gabriel Valley in 1987 and resulted in 200 injuries and at least three deaths.

Caltech seismologists also said the quake was along the Elysian Park Fault.

The epicenter of the earthquake that struck Southern California last week was in the southernmost end of the Central Valley, about 100 miles north of Monday's quake. It was followed by two aftershocks of a magnitude measuring over 4.0 within just 10 minutes.

"That's a pretty active sequence for this very short amount of time since the event," Jones said at the time.

Seismologists say the possibility of aftershocks is highest right after an earthquake and that probability declines with time. But each quake, even small tremors, can raise the likely of another one.

"Each of those aftershocks could trigger another earthquake," Vidale said of the many tremors near Bakersfield last week.

"This sequence had more aftershocks than most," he noted. "And so that also raises the odds of future activity a little bit."

USGS did not report aftershocks within an hour following Monday's earthquake in Los Angeles. The night before, just before 11 p.m., a 2.9-magnitude temblor struck an area near Big Bear Lake, which is about 90 miles east.