July 19, 2017 UPDATE: The University of Utah Seismograph Stations (UUSS) is monitoring an earthquake swarm which is currently active on the western edge of Yellowstone National Park. The swarm began on June 12th, 2017 and, as of 09:45 MDT on July 19th, 2017, is composed of 1,284 events with the largest magnitude of ML 4.4 (MW 4.4) (Figure 1). The swarm consists of one earthquake in the magnitude 4 range, 7 earthquakes in the magnitude 3 range, 105 earthquakes in the magnitude 2 range, 407 earthquakes in the magnitude 1 range, 736 earthquakes in the magnitude 0 range, and 28 earthquakes with magnitudes of less than zero. These events have depths from ~0.0 km to ~14.0 km, relative to sea level. At the time of this report, there were 125 felt reports for the M4.4 event that occurred on June 16, 2017 at 00:48:46.94 UTC (June 15, 2017 at 18:48:46.94 MDT). The M4.4 event has an oblique strike-slip moment tensor solution (Figures 1 & 2). In addition, four other earthquakes in the swarm have been reported felt.
Figure 1. Location of the earthquakes that are part of the swarm as of July 19, 2017 at 09:45 MDT (red symbols).
Figure 2. Moment Tensor solution for the M4.4 event showing the fit between data (black) and synthetics (red dashed).
Figure 3. Animation of the June 2017 Yellowstone earthquake swarm. Earthquakes appear as red circles as they happen, then transition to blue. After they have occurred, they appear as black circles. The size of the circles are proportional to the earthquakes magnitude.
Earthquake swarms are common in Yellowstone and, on average, comprise about 50% of the total seismicity in the Yellowstone region.
UUSS will continue to monitor this swarm and will provide updates as necessary.
If you think you felt an earthquake, please fill out a felt report at: http://earthquake.usgs.gov/earthquakes/dyfi/.