A 4.3-magnitude earthquake jolted a lake shoreline Friday, July 11, in Southern California, the U.S. Geological Survey reported. Then dozens of smaller quakes followed. The 6.5-mile-deep quake hit more than 7 miles from Calipatria at 2:55 a.m., according to USGS.

A minor, 3.7-magnitude earthquake struck in Southern California on Thursday. It was followed by a larger, 4.3-magnitude quake nearby a few hours later, according to the United States Geological Survey.

According to their study, published today in the journal Science, the Android Earthquake Alerts (AEA) system’s efficacy rivaled traditional seismic networks in its ability to detect seismic activity and deliver alerts.

Google’s Android Earthquake Alerts program is a globe-spanning earthquake early-warning system that uses billions of phone sensors to detect seismic shaking and alert those at risk

It has been several years since a magnitude 5.2 or greater earthquake hit Southern California, and Tuesday’s quake was the strongest to strike the region in three years.

Numerous moderate earthquakes have occurred along the Calaveras Fault, including the 6.2 Morgan Hill earthquake in 1984, according to USGS.

The fault has moved the curbs as much as a handspan, around 18 centimeters, since the time they were installed, up to 60 years ago.

Southern California’s last magnitude 7.9 earthquake occurred in 1857, when the San Andreas ruptured between Monterey and Los Angeles counties.