More than 50 small earthquakes have been recorded since Wednesday near the town of Fillmore in Ventura County, according to a U.S. Geological Survey seismologist.
The biggest of the quakes registered magnitude 2.7, and the vast majority were less than magnitude 2.0, so it's unclear whether people felt them.
According to a USGS map, the intensity of the 2.7 quake was limited to a fairly small area in rural Ventura County. That quake hit three miles east of Fillmore and six miles west of Santa Paula.
On whether these small quakes signal a bigger quake, seismologist Lucy Jones said on Twitter all earthquakes "make another more likely, so probably have more." But she said there is no way to know if one will be bigger.
Swarms of small earthquakes are not uncommon in California.
In 2014, Mammoth Lakes experienced more than 700 small quakes. Countless small faults crisscross the area known as the Long Valley Caldera. This roughly 20-mile-wide crater-like depression, adjacent to Mammoth Mountain, was formed from ash and pumice deposits during a volcanic "super eruption" about 760,000 years ago.
In 2012, a swarm of quakes hit Imperial County, including two greater than magnitude 5.