Excerpts from press release issued by Yellowstone Volcano Observatory.
30 March 2014 – West Yellowstone, Montana
yellowstone-30Mar
The epicenter of the magnitude 4.8 shock was located 4 miles north-northeast of Norris Geyser Basin in Yellowstone National Park, Wyoming.
This earthquake is part of a series of earthquakes that began in this area on Thursday, March 27. As of 8:15 am today, this series has included at least 25 earthquakes in addition to the main shock, with the largest of magnitude 3.1.
The magnitude 4.8 main shock was reported felt in Yellowstone National Park and in the towns of West
Yellowstone and Gardiner, Montana.
Today’s event is the largest earthquake at Yellowstone since February 22, 1980, and occurred near the center of a region of recent ground uplift described in a YVO Information Statement on February 18, 2014. The Yellowstone Volcano Observatory has been tracking this uplift episode for about 7 months.
According to the Italian website expianetadidio.blogspot.it, this earthquake is not associated with volcanic activity.
However, it is a continuation of the ground deformation that has been occurring during the last two months, which was reported in a statement on February 18, 2014. At that time the University of Utah reported 245 earthquakes in the region of Yellowstone National Park.
Seismicity at Yellowstone in February was characterized by a continuous swarm of 153 earthquakes about 5 miles NW of Norris Geyser Basin, YNP, which persisted throughout the month.
http://earthquake.usgs.gov/earthquakes/eventpage/uu60061837#summary
Thanks to Jack Hydrazine and Alessandro Decet for these links