4.2 magnitude earthquake rattles Northern California

A 4.2 magnitude earthquake was felt across California’s Sacramento County and parts of the Bay Area on Wednesday morning, according to the United States Geological Survey (USGS).

The quake hit southern Sacramento at 9:29 a.m, exposing the towns of Rio Vista and Isleton to “moderate” shaking. It was initially estimated to be magnitude 5.7, but was downgraded.

There was light shaking across 5 nearby towns, including Oakley and Discovery Bay, and weak shaking in Sacramento, San Francisco, and San Jose, the USGS said.

There were no immediate reports of damage or injury.

An emergency alert instructing people to “Drop, Cover, [and] Hold On” was sent to mobile phones across the area, reported NBC affiliate KCRA.

The San Francisco Bay Area train service BART delayed trains for 5-8 minutes to conduct track inspections.

The earthquake struck at a shallow depth of 6.7 miles from the earth’s surface, according to the USGS. The intensity of shaking during an earthquake diminishes as the depth increases. That’s why the 4.8 magnitude earthquake which hit California at a depth of 19.2 miles on Monday had a lower impact.

The earthquake struck just a day before the statewide Great California ShakeOut earthquake drill, where 10.1 million people across the state will practice how to be safer during large earthquakes.

According to the California Earthquake Authority, most Californians live within 30 miles of one of the more than 500 active fault lines running across the state.

USGS estimates say there is 75% chance that at least one 7.0 magnitude or greater earthquake strikes Southern California in the next 30 years.