Earthquake swarm in desert fading away   The swarm of
earthquakes that shook San Diego County on Sunday is fading
away, though there's a chance that it could come back to life at
any time, says the U.S. Geological Survey.  "These swarms tend
to last only one, two or three days," says Susan Hough, a
seismologist at the USGS in Pasadena. "We're not really sure
why. We don't know that much about them."  An area south of the
Salton Sea, between the San Andreas and Imperial faults, erupted
with quakes early Sunday. By midnight, more than 40 quakes
measuring from 3.0 to 5.5 had been recorded. The shaking
included a 5.3 event at 11:33 a.m. and a 5.5 at 1:57 p.m. The
quakes caused some damage in nearby Brawley.  On Monday, the
shaking greatly declined. There were only five quakes measuring
3.0 or higher. The largest event was a 4.2 at 7:01 p.m.  Quake
swarms can cause a lot of anxiety, especially when they're on or
near the San Andreas. But Hough noted that there hasn't been a
single case in the past century when a l