NASA's Earth Observatory image of the day is of the recent earthquake swarm near Hawthorne, Nevada. Over 400 quakes have been recorded since April 10 ranging from magnitude 1.0 to 4.6. The active area is near the Aurora-Bodie Volcanic Field, although the events are considered to be tectonic rather than volcanic in origin. [right, NASA Earth Observatory image by Robert Simmon, using data from Landsat 7 and the Nevada Seismological Laboratory]
There are some analogies to the San Francisco Volcanic Field near Flagstaff, where the bulk of Arizona's seismic activity occurs.