Quoting their latest statement:
Through 5 January 2009, seismic activity has markedly decreased. It is possible that the swarm has ended, though a return of activity may occur as Yellowstone swarms of the size usually last for tens of days to many weeks.
About 500 earthquakes occurred between Dec. 26 through Jan. 1. Three hundred of the earthquakes (including all >M2.0) have been reviewed by seismologists. There have been 86 earthquakes with M > 2.0 and 16 earthquakes > M3.0. About 200 smaller earthquakes have yet to be reviewed. Depths are difficult to determine accurately. The best located earthquakes have depths on the order of 3 to 10 km (1.8 to 6.0 miles). From Dec. 26 through Jan 2, the earthquake hypocenters appear to have migrated northwards, starting southeast of near Stevenson Island, with many of the latest events occurring near Fishing Bridge.
The recent swarm is well above typical activity at Yellowstone. Nevertheless it is not unprecedented during the last 40 years of monitoring. Swarms are the typical mode of occurrence of earthquakes within the Yellowstone caldera, with magnitudes ranging to > 4.0. The 1985 swarm on the northwest rim of the caldera lasted for three months, with earthquakes up to M4.9 and over 3000 total events recorded.
Interesting. Most valuable, to my mind, is the discussion on the 1985 swarm, which provides some needed context.
It also suggests that, barring a sudden return in activity, that this is an event to notice, but not to worry about.
