February 2004 Yellowstone Seismicity Summary
During February 2004, 55 earthquakes were located in
the Yellowstone region. The largest shock to occur
during this period was a magnitude 2.1 earthquake
on February 24 at 5:41 PM MST, located about 3.4
miles north northeast of Fishing Bridge, Wyoming.
Earthquake activity in the Yellowstone region is at
background levels.
http://volcanoes.usgs.gov/yvo/activity.htmlFrom the USGS-CVG website concerning the quakes on Mt. St. Helens the day prior to the eruption:
May 17 - The mountain remained quiet. Seismic activity reached the lowest level for May, with only 18 earthquakes larger than 3.0 recorded (including 6 larger than magnitude 4.0). In response to pressure from property owners and with the Governor's consent, law enforcement officials escorted about 50 carloads of property owners into the Red Zone to retrieve possessions. Those who entered were required to sign liability waivers at the roadblocks and to leave by nightfall. Authorities agreed to allow another caravan of property owners in at 10:00 a.m. the following morning.From this it is evident large earthquakes are not necessarily a prerequisite of imminent eruption. Smaller and/or swarm quakes are every bit as indicative that something may be up (figuratively.