A series of small earthquakes rattled central California, beginning Sunday evening and continuing into Monday, but the U.S. Geological Survey (USGS) says there is no cause for alarm. The phenomenon, called an earthquake swarm, is actually fairly common in regions with a high level of geological activity (such as California). Despite the number of quakes—18 or more within a day’s time—the strongest registered a magnitude 3.7, which is not very strong as earthquakes go and no significant damage has been reported.
With a sharp increase in earthquake activity, one might wonder whether bigger quakes are on the way. But USGS reports that swarms like this have not been connected to larger earthquakes occurring in the same region. The agency’s definition of an earthquake swarm, or seismic swarm, is actually fairly loose, referring simply to a cluster of small quakes happening in one area with no requirement for a set time period. The quakes don’t even have to occur along the same fault line to be considered part of the swarm.
The earthquake swarm in California may already be over, or additional tremors may still be on the horizon, but it’s unlikely they will lead to anything more substantial. Yellowstone National Park has seen a number of earthquake swarms over the years, with the largest happening in 2004, 2009, and 2010. That most recent swarm included more than 2,000 quakes over the course of a month. Although several registered a magnitude over 3.0, the swarm didn’t lead to any type of larger earthquake or other catastrophic event.