Interesting parts of a University of Utah press release:
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.
The University of Utah Seismograph Stations reports that a light earthquake occurred at 06:34 AM on March 30, 2014 (MDT). 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.
http://earthquake.usgs.gov/earthquakes/eventpage/uu60061837#summary
