The magnitude 3.6 earthquake that rattled Berkeley early Thursday morning was followed by three smaller quakes that night.
At 6:51 p.m. Thursday, a magnitude 1.4 quake hit, trailed by a magnitude 1.1 and a magnitude 1.3 at 7:12 p.m. and 7:50 p.m., respectively, according to the U.S. Geological Survey.
At 12:15 a.m. Saturday, another magnitude 1.1 quake shook Berkeley, with an epicenter near Stern Hall on the UC Berkeley campus. With these three additional quakes, Berkeley has now seen 13 earthquakes — ranging from magnitude 1.0 to 4.0 — since Oct. 20, when a 4.0 magnitude temblor first shook the city.
According to Jack Boatwright, a seismologist with the U.S.G.S., multiple earthquakes of similar magnitudes that come within a short time span are called a “swarm.” They differ from the typical main shock-aftershock sequence in which the first quake is one magnitude unit greater than those that come after it.
Before these smaller quakes hit Thursday night, Boatwright told The Daily Californian that an increase in the frequency of earthquakes in Berkeley could signal that the “Big One” — an earthquake of magnitude 6.7 or greater — is on its way.
He added that, before this month’s quakes, the last time the Hayward Fault saw a swarm of earthquakes in Berkeley was in 2006.
Thursday’s magnitude 3.6 and 1.4 quakes both caused light shaking and no damage, according to the agency.
Soumya Karlamangla is the assistant city news editor.
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