Ongoing Yellowstone Earthquake Swarm North of West Yellowstone, MT.

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).

Moment Tensor for M 4.5

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:

Yellowstone swarm continues with M 3.6 felt near West Yellowstone, MT

Released: July 18, 2017 03:15 PM MDT

The University of Utah Seismograph Stations reports that a minor
earthquake of magnitude 3.6 occurred at 02:31 PM on July 18, 2017
(MDT). The epicenter of the shock was located 9.3 mi N of W.
Yellowstone, MT. This earthquake is part of an ongoing sequence
of earthquakes that began on June 12, 2017 and included a
a magnitude 4.4 event on June 15, 2017, 9.0 mi NNE of W.
Yellowstone, MT. Today’s M 3.6 earthquake was reported felt in
Yellowstone National Park and in West Yellowstone, MT. It was
followed by numerous smaller earthquakes, the largest of which
had magnitudes of 2.8 and 2.9. The total number of located
earthquakes in the current sequence has now exceeded 1200.

Anyone who felt the earthquake is encouraged to fill out a survey form
either on the Seismograph Stations website: or the
US Geological Survey website:

Earthquake Summary:

Date (UTC): July 18, 2017 Time (UTC): 20:31

Date (local): July 18, 2017 Time (local): 02:31 PM MDT

Latitude: 44 47.25′ N

Longitude: 111 2.27′ W

Preferred magnitude: 3.60 Ml

1928 – Helena, MT – M 5½ ±

Intermountain Seismic Belt Historical Earthquake Project

February 29, 1928 – Helena, MT – M 5½ ±

The 1928 Helena, Montana earthquake had no reported injuries or damage. The shaking startled people throughout the city of Helena and was more noticeable on upper floors of buildings with two or more stories above ground. The shaking was severe enough to disrupt a trial in one city courthouse. Without taking time to formally adjourn the proceedings, the judge and others fled the courtroom as the shaking began.

The earthquake was reported felt in areas southeast of Helena including: Trident, Three Forks, Manhattan, Logan, Lombard, and Sixteen-Mile Canyon. White Sulphur Springs, to the east of Helena, also reported earthquake shaking.

There were reports of shaken buildings, windows rattling, furniture moving, and goods being shaken from shelves.


For additional information about this earthquake:

Earthquake Summary 3D Newspaper Articles 3D Blank Thumbnail Blank Thumbnail

For more information about this project:

ISB Hist EQ Proj


Magnitude 3.4 Arizona earthquake near St. George, UT


University of Utah Seismograph Stations 

Released: July 12, 2017 09:10 AM MDT

The University of Utah Seismograph Stations reports that a minor earthquake of magnitude 3.4 occurred at 08:41 AM on July 12, 2017 (MDT).  The epicenter of the shock was located nine miles SSE of St. George, UT.  A total of 6 earthquakes of magnitude 3.0 or greater have occurred within 16 miles of the epicenter of this event since 1962. The largest of these events was a magnitude 5.9 on September 02, 1992, two miles SSE of Washington, UT.

Today’s earthquake was reported felt in Saint George, UT and surrounding cities.

Anyone who felt the earthquake is encouraged to fill out a survey form either on the Seismograph Stations website: or the US Geological Survey website:

Earthquake Summary:

Date (UTC):   July 12, 2017         Time (UTC):   14:41

Date (local): July 12, 2017           Time (local): 08:41 AM MDT

Latitude:     36º 58.79′ N

Longitude:    113º 33.96′ W

Preferred magnitude: 3.40 Ml