Three large earthquakes in last 2 years near Fresno , California . Swarms of earthquakes not uncommon in the region . Last series of earthquakes of over 2500 between 1997 - 98 .
Three dozen earthquakes in last 2 days near Fresno , California . Swarms of earthquakes not uncommon in the region . Last swarm of earthquakes produced over 2500 between 1997-98 .