More than 100 small earthquakes have been recorded near The Geysers geothermal field in Northern California since just after midnight on Thursday.
According to the SF Gate, the largest was a magnitude 4.0 quake that struck at 12:48 a.m., followed by a series of smaller tremors. USGS seismologist Susan Hough described the event as a “swarming sequence,” noting that this area in Mendocino County is well known for seismic activity.
The tremors are not located on any currently mapped faults. While only a few dozen people reported feeling the quakes, experts say there is a chance for more activity in the area.