The USGS says the quake struck less than two miles west-southwest of South El Monte at 11:38 p.m., with a depth of about 10 miles.
Seismologist Dr. Lucy Jones told Eyewitness News the quake was similar in type and location to the deadly 1987 Whittier-Narrows quake which had a magnitude of 5.9. But this one was much smaller in power.
"Here in Pasadena I felt it," Jones said. "It woke me up."
She added that there were at least two aftershocks, measuring 2.1 and 1.6. She also said there is a 5% chance that it was a foreshock to a larger quake.
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There is also about a 50% chance of additional small aftershocks within the next 24 hours, she said.
The earthquake was initially estimated at 4.8, then downgraded to 4.6 and then to 4.5.
A shake map produced by the USGS indicates the rattling was felt south to San Diego, north to Santa Barbara and east well out into the Inland Empire and the Mojave Desert, as well as off the coast on Catalina and Santa Cruz islands.
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There were no immediate reports of significant damage or injuries, but local police and fire departments said they were on alert and surveying their communities for damage.
Los Angeles International Airport also reported not finding any damage.
What a jolt! We felt it too. No need to call 9-1-1 unless you have an emergency.— San Gabriel Police Department (@SanGabrielPD) September 19, 2020
No damage or injuries reported so far. https://t.co/QATlFKleIi
⚠️ #Earthquake ⚠️ Felt Widely in #LosAngeles. Prepare Now For Aftershocks. If Inside When Shaking Starts: DROP, COVER, HOLD ON! Protect Your Head + Neck While Taking Cover Under Sturdy Furniture or Near a Sturdy Interior Wall, Away From Windows and Doorways Until Shaking Stops.— LAFD (@LAFD) September 19, 2020
Your @LAFD is in Earthquake Mode, with all 106 Neighborhood Fire Stations checking their areas for damage.— Chief Terrazas (@LAFDChief) September 19, 2020