Caltech seismologist Kate Hutton said there are a lot of magnitude-4.4 earthquakes, but they're not quakes that we talk about all the time because they tend to happen in areas that are not very populated.
"Probably the best way to view it is that it's an earthquake drill," she said. "It reminds you to get your stuff together and your plan and make sure everything is kosher in case we have a bigger one one day."
Hutton described the quake as a thrust earthquake.
"That just means that the one side of the felt slides up over the other side," she said.
CalTech seismologists consider a 4.4-magnitude temblor a "light" earthquake, too light to cause much damage beyond cracked walls and windows. And no injuries.
But where it hit, they say, indicates stresses building up for an even bigger earthquake.
"You can think of them as creaking of the ground before the big earthquake happens," said CalTech seismologist Egill Hauksson. "So they're telling us stress is building up on these major faults. So these earthquakes are telling us these faults are active and they're getting ready for something, but we don't know when or how big."
Hauksson said Tuesday morning's quake was centered in the Whittier Narrows. That's just a few miles from the epicenter of a 5.9-magnitude in 1987 that killed eight people, but was probably not on the same fault.
That area remains seismically active, along with related faults that stretch from Elysian Park in L.A. through Whittier, Chino, Elsinore and all the way to Borrego Springs, where a 4.2 quake rattled the desert just three days ago.
"We need to be worried about the future. We need to be prepared, and if we're prepared, we're all going to be OK," said Hauksson. "So have your earthquake supplies, have your food and water for three days, and make sure things are safe around your house -- not big bookcases that are going to fall on people. Do the obvious preparedness."
There have been no aftershocks.
Theresa Hernandez said she was up at the time cleaning her cabinets at her Pico Rivera home, and the quake scared her. "They say you have to be ready, but you're never ready," she said. "My legs are still shaking."
Pico Rivera resident Randy Gonzales said the earthquake was not the way he wanted to start his 50th birthday. He said the quake caused an old crack in the driveway to grow and added new cracks in two double-pane windows.
Gonzales said since he lives off of Paramount Boulevard, he thought the rattle was a car accident.
"When it continued to shake, it was like, 'no, that wasn't a car,'" he said.
Although the quake was not strong enough to cause major damage, it was strong enough to wake most residents across the Southland, like Pico Rivera resident Andrew Nava.
"I actually thought it was my girlfriend waking me up, telling me to take the dog out," he said.
Norwalk resident Santiago Chamber, who is a safety officer at Children's Hospital and trained in emergency preparation, said his family instantly went into emergency preparedness mode.
"After the shaking subsided, we immediately went to check for the children, and they were really excited about using the training that we've practiced so many times, so they went into the dining room area and got under the table," he said.
About half the people Eyewitness News spoke with said they were prepared if the quake had been worse.
"We do have emergency kits in the back," said Palisa Ortiz of Pico Rivera. "We have flashlights, canned goods, stuff like that."
Hutton said anytime there's an earthquake in California, there's a 5 percent chance that it's a foreshock to something bigger.
"There is a small risk, but the most likely scenario is that we would see a few aftershocks, maybe one or two magnitude 3s and some 2s, so people might feel another shake today," she said.
There have been no reports of aftershocks.
The California Highway Patrol closed lanes on the southbound 5 Freeway in Downey because of damage to the freeway, but Caltrans determined the damage was not related to the quake. It was simply wear-and-tear to the lane, and repairs had already been under way.
Tuesday's earthquake hit in the same general area as the Whittier Narrows earthquake in 1987, when a 5.9-mag. quake struck on Oct. 1 at 7:42 a.m. The '87 quake killed three people and caused about $358 million in damage.