Earthquake swarms are mysterious, but usually not threatening. Living in northern California, I've seen lots of themI even have played with them. But the March-April swarm in the Reno area is unusual. First, it has lasted longer than typical swarms. Second, it hasn't yet reached a peak. Third, the events are quite shallow. Fourth, it has gotten a formal name, the 2008 Mogul-Somersett sequence. To follow daily developments, bookmark the University of Nevada Reno's special page for the west Reno swarm.
Nevada geologist Silver Fox, of the Looking for Detachment blog, is wondering whether the quake swarm is being triggered somehow.