A magnitude-4.4 earthquake centered in the San Gabriel Valley east of Los Angeles caused widespread shaking Tuesday night.
The 7:33 p.m. quake was located near La Verne, about 30 miles east of downtown LA, but residents from the coast to inland areas reported shaking.
The earthquake was felt in cities across Southern California, with people calling into NBC4 saying they felt the quake in cities far and wide, including Arcadia, Glendora, West LA, Manhattan Beach, Tustin, Corona, Culver City, Rancho Cucamonga, Bellflower, Valencia, Sherman Oaks, Studio City, Fullerton, Rialto, La Crescenta, Culver City, Fontana, Santa Clarita, Irvine, Hisperia, Lakewood, Burbank and Anaheim.
The initial tremor was followed by a 3.4 magnitude earthquake near the same area, which was recorded at 7:34 p.m. per the USGS.
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Seismologist Lucy Jones said the quake should not be expected to have done damage to structures. Jones said the quake, felt as far away as Bakersfield and Oceanside, was not on the Sierra Madre fault, one of the largest in the region. The complex fault zone is divided into five main segments, some of which are parallel and branching faults.
The earthquake was the largest in Southern California since Dec. 29, 2015, when a magnitude-4.3 quake struck near Devore, in San Bernardino County, Jones said.
A 5.1-magnitude earthquake struck in La Habra on March 28, 2014.
"This is a very ordinary earthquake for California, the size that we have several times a year somewhere in the state," Jones said.
More than a dozen small aftershocks were felt and as is always the case, there was about a 5 percent the largest magnitude-4.4 earthquake would be followed by a bigger one, Jones said.
The La Verne Police Department put out a note on social media shortly after 8:00 p.m. Several agencies conducted surveys, but there were no reports of damage. The Los Angeles County Fire Department said it went into "Earthquake Mode" but officially announced that that designation had been lifted at 8:41 p.m.
Students at the University of La Verne were evacuated after the quake.
The quake provided a test for California's nascent earthquake early-warning system. The system sent out a warning a few seconds before the shaking began.
The earthquake early-warning system is under development by the U.S. Geological Survey and is only available to a limited array of testers, but it is expected that more people will be eligible to test the system later this year. The shaking from an earthquake travels at the speed of sound through rock, which is slower than the speed of today's communications systems. For example, it would take more than a minute for a magnitude 7.8 earthquake that starts at the Salton Sea and travels up the state's longest fault, the San Andreas, to shake Los Angeles, 150 miles away.
An early-warning system would give LA residents crucial seconds, and perhaps even more than a minute, to prepare.
A seismic early-warning system for the West Coast has been under development for years by the USGS, the nation's lead earthquake monitoring agency, but the project has remained short of funds.
It's estimated that building a full system covering the West Coast would cost at least $38.2 million, with about $16.1 million annually to operate and maintain it.
The USGS has said it planned to begin issuing limited public alerts from the system by the end of this year, as long as funding wasn't cut. Southern California is one area where the network of seismic sensors is dense enough at present to begin early warnings.
For the system to go live all along the West Coast, more sensors need to be installed in Washington, Oregon and sparsely populated areas of Northern California. More than 850 earthquake-sensing stations are online, but about 800 more are needed, officials said.
Too few sensors could mean, for example, that Los Angeles would experience delays in warnings from an earthquake that starts in Monterey County and barrels south along the San Andreas fault.
Along the West Coast, facilities including airports, oil refineries, pipelines, schools, universities, city halls and libraries are already testing or planning to test the system.