Magnitude 4.2 earthquake strikes near Isleton in the Delta, triggers ShakeAlert warning
ISLETON, Sacramento County -- A magnitude 4.2 earthquake struck near the community of Isleton in the Sacramento-San Joaquin Delta on Wednesday morning.
According to the U.S. Geological Survey, the earthquake struck at 9:29 a.m. about three miles southwest of the town. The earthquake was originally reported as a magnitude 4.6 but was downgraded several minutes later to a magnitude 4.1. Later still, the USGS re-evaluated the earthquake to a 4.2.
There were no immediate reports of damage or injuries from the earthquake.
Shortly after the earthquake, BART announced that trains were being held as crews conducted track inspections. As of 9:55 a.m., officials said inspections had concluded and that normal train service had resumed.
According to the USGS website, shaking was felt in much of the East Bay, particularly in eastern Contra Costa County, along with parts of Solano County. Shaking was also reported in the Sacramento area.
The agency confirmed that the ShakeAlert early warning system was activated, pushing earthquake alerts to phones across the region. Alerts were received on phones in the KPIX newsroom in San Francisco, nearly 50 miles from the epicenter.
For many who received alerts on their cell phone, the earthquake initially was reported with a magnitude of 5.7. The USGS said that is perfectly normal.
"The initial magnitude has to be estimated extremely quickly, just within a couple of seconds of the earthquake starting, in order to be able to provide a useful alert to the population," said USGS Research Geologist Belle Philibosian.
While Wednesday's alert was not a drill, the California Office of Emergency Services is planning to issue a test alert on Thursday, October 19, 2023 at 10:19 a.m. for users of the MyShake app, as part of the Great California ShakeOut, an annual drill to test earthquake preparedness.
The earthquake also happened on the same week as the region marked 34 years since the Loma Prieta Earthquake, the strongest and most destructive earthquake to hit the Bay Area since 1906.
Wednesday's quake is the third above magnitude 4.0 to strike Northern California this week. On Monday, a magnitude 4.8 quake followed by a magnitude 4.1, struck near the Humboldt County coast. No damage or injuries were reported from either quake.
CalOES also has more information on earthquake preparedness on its website.
