Less than 12 hours after a , another temblor with a magnitude of 4.5 shook the same area, according to the U.S. Geological Survey. It was followed by a magnitude-3.4 aftershock that hit in the same area at 9:51 a.m.
The epicenter of the larger earthquake, which hit at 9:33 a.m. Wednesday, was about 2 miles north-northeast of Yorba Linda, Calif., and about 29 miles east-southeast of downtown Los Angeles, according to the USGS.
People near the epicenter described it as a short jolt that rattled windows. No damage was reported.
The temblor was felt in downtown Los Angeles, where the Los Angeles Fire Department went into "earthquake emergency mode," fire department spokesman Brian Humphrey said.
"No significant damage or injuries were reported," Humphrey said.
Metro operated all its rail lines at a reduced speed of 15 mph for post-earthquake inspection. Normal service was expected to resume after 10 a.m.
More than 4,600 people in 458 ZIP codes reported feeling the temblor as of noon, according to the USGS Community Internet Intensity Map. (Submit your own "Did You Feel It?" report.) People from as far south as San Diego and as far north as Lancaster reported shaking.
Within a half hour of the first temblor, five more earthquakes, ranging in magnitude from 1.2 to 3.7, struck the same general area, according to the U.S. Geological Survey. Since then, even more earthquakes have hit the area.
USGS representative Kate Hutton in Pasadena said there have been about 30 quakes in the area of the Whittier Fault since Tuesday night, "three of which were big enough for people to feel," referring to the pair of 4.5 quakes and the magnitude-3.4.
"This is all part of the same earthquake sequence, they're all in the same area," Hutton said. "There's a couple of ways to look at the sequence. One is that it's a double earthquake with two main shocks. Normally an earthquake sequence has one main shock followed by aftershocks that are smaller and maybe a few fore-shocks that are smaller. Or it could be considered an earthquake swarm, where there's a series of earthquakes that are about the same size or smaller.
"Either way, this is fairly common activity in California. We haven't had anything in the L.A. basin in the last few years but that doesn't mean we're totally quiet, and we certainly have been active in the southern part of the state," she said.
Did you feel the latest quake? How many quakes or aftershocks have you felt since Tuesday night?
—City News Service and Patch editor Kelly Hartog contributed to this report.