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Interesting earthquakes or sequences

2020 Magna Earthquake Sequence FAQ

Posted on by Paul Roberson

Updated March 10, 2021 with additional information on the Magna Sequence here.

Magna earthquakes March 18, 2020 - Feb 2021

How many earthquakes have we had in the area?
The University of Utah Seismograph Stations (UUSS) has located 2,590 earthquakes that occurred in the Magna, Utah, area from March 18 through February 28, 2021(Figure 1). The largest of these earthquakes was the magnitude (M) 5.7 mainshock that occurred at 7:09 am MDT on Wednesday, March 18, 2020. The remaining 2,589 earthquakes are aftershocks. The largest aftershocks were two M 4.6 events that occurred at 8:02 am and 1:12 pm on Wednesday, March 18, 2020. A M 4.2 aftershocks occurred on April 14 and 17th which were widely felt along the Wastach Front. There have been 36 aftershocks of M 3 and larger. We continue to locate new earthquakes as they occur.

Magna earthquakes March 18, 2020 - Feb 2021 magnitude vs Time plot

What is a Foreshock, Mainshock, or Aftershock?

Mainshocks, foreshocks, and aftershocks are all earthquakes. The mainshock is the largest magnitude earthquake in an earthquake sequence. It may be the first event in the sequence or occur later. The earthquakes in the sequence that occur before the mainshock are called foreshocks and the ones that occur after are called aftershocks. Sometimes an earthquake that is initially called the mainshock is reclassified as a foreshock because a larger earthquake follows it. An earthquake sequence is a group of events that occur close together in time in the same area.

What is the difference between UUSS and USGS?

The University of Utah Seismograph Stations (UUSS) and the U.S. Geological Survey (USGS) are partner agencies. All seismic data from the Utah region are collected and initially processed by UUSS. The resulting earthquake locations, magnitudes, and ShakeMaps are submitted to the USGS, which serves the information on a USGS website. USGS personnel often provide additional information on their website related to how the earthquake ruptured, how widely the earthquake was felt, the potential economic and life impacts, and the chances of aftershocks and landslides. As members of the Advanced National Seismic System (ANSS), UUSS and USGS work together to provide the most accurate and complete information about earthquakes in the Utah region.

We had a 5.7 earthquake, what are the percentages of having a larger earthquake soon?

Most likely, the 5.7 earthquake will end up being the biggest earthquake in this sequence and so it will be called the mainshock. There is a small chance, roughly one-in-twenty (5%), that a larger earthquake will occur in the next 5-6 days after the mainshock. In that case, the 5.7 earthquake would be redesignated as a foreshock, and the new, larger earthquake will be called the mainshock.  A “larger” earthquake means any earthquake bigger than the one that just occurred, even if it is only 0.1 magnitude units bigger. The probability of an earthquake being a foreshock to an earthquake that is one or two magnitude units larger is much smaller than one-in-twenty.

How long did the mainshock last?

How long you felt the shaking would depends on where you were.  For the 
Magna Earthquake, if you were downtown, the strongest shaking lasted around 4-6 sec.  However, the shaking was strong enough to be felt for about 20 sec.

Will this delay or trigger “the big one?”

No, small earthquakes do not relieve enough stress in the earth to reduce the likelihood of a large earthquake. We are still at risk of a magnitude 7-7.5 earthquake (the “Big One”) occurring somewhere along the Wasatch fault. The risk is similar to what it was before the Magna sequence. 

How will I be notified of the next earthquake?

Anyone can sign up for Earthquake Notification Service (ENS) and receive emails or text messages about earthquakes as the locations are published. You may set up your own geographic area and magnitude threshold. All UUSS earthquake locations are sent out via the ENS system. Sign up here.

Will the ground open up or Fracture from the 5.7 earthquake?

It is unlikely for the fault rupture from the 5.7 earthquake to reach all the way to the surface and create what we call a scarp. It is possible that shaking from the 5.7 created liquefaction features at the surface near the epicenter. 

Why can’t Utah get a M9.0 Earthquake?

The bigger an earthquake is, the more space on a fault it takes up. The faults in Utah simply are not big enough to accommodate an M9 earthquake.

How does the earthquake depth affect the shaking  and how do you measure the depth?

The shallower the depth of an earthquake, the stronger the shaking will be near the epicenter; however, the strength of shaking will fall off more rapidly away from the epicenter. It is the same idea as aiming a flashlight at a wall and walking toward the wall. The closer you get to the wall the more intense the light becomes, but it takes up a smaller area. Earthquake depth is measured from the arrival times of seismic waves, similar to how the epicenter is determined.

Are earthquakes more common now? 

No. There is no evidence for change in the overall rate that earthquakes occur.

More information from Earthquakes.utah.gov

What can I do to be prepared?
 An excellent source of information on earthquake preparedness is the publication “Putting Down Roots in Earthquake Country”.

Upper Geyser Basin Seismic Imaging Experiment

Posted on by Paul Roberson

In the Fall of 2015 and 2016, The University of Utah, in collaboration with the National Park Service and the University of Texas at El Paso installed dense seismic arrays centered on Old Faithful Geyser in Yellowstone National Park.  The goals of this project are to image the shallow velocity structure beneath and around Old Faithful in order to identify areas of shallow, active hydrothermal activity as well as to learn more about these hydrothermal systems, in particular Old Faithful.  The Upper Geyser Basin (Figure 1), where Old Faithful is located, has one of the highest concentrations of hydrothermal features in the world.

Figure 1: The Upper Geyser Basin near Old Faithful (red star) with the main roads in white.
Figure 1: The Upper Geyser Basin near Old Faithful (red star) with the main roads in white.

In November of 2015, 133 seismometers were deployed for 2 weeks (Figure 2) collecting continuous passive seismic data.  The average station spacing was ~50 meters and the aperture of the entire array was ~1 km.

Figure 2: The 2015 deployment of 133 seismometers (yellow circles) around Old Faithful (red star).
Figure 2: The 2015 deployment of 133 seismometers (yellow circles) around Old Faithful (red star).

In November of 2016, in order to achieve a higher station density, a different approach was taken in that smaller dense arrays with ~20 meter spacing were deployed for 24-48 hours and then were moved to different locations around Old Faithful for another 24-48 hours until the area of interest was covered (Figure 3).  In addition, while each individual array was in, we did active seismic sources using a sledgehammer throughout the array.  A subset of instruments was deployed in the same location throughout the experiment in order to tie all the individual sub-arrays together.

Figure 3: The 2016 deployment of 519 individual locations (circles). The stations are color-coded by how long they were deployed. Green circles represent seismometers that were deployed in the same location for the entire time-period of the experiment. Each individual array (labeled 1-7) were deployed for 24-48 hours.
Figure 3: The 2016 deployment of 519 individual locations (circles). The stations are color-coded by how long they were deployed. Green circles represent seismometers that were deployed in the same location for the entire time-period of the experiment. Each individual array (labeled 1-7) were deployed for 24-48 hours.

Data are being analyzed to image the shallow subsurface beneath the Upper Geyser Basin near Old Faithful.

2019 Bluffdale Earthquake Sequence FAQ

Posted on by Seis Moe
Seismicity near Bluffdale, Utah Feb 13- April 20

How many earthquakes have we had in the Bluffdale area?
 The University of Utah Seismograph Stations (UUSS) has located 191 earthquakes that occurred in the Bluffdale, Utah, area from February 13 through April 20 (Figure 1).  The largest of these earthquakes was the magnitude (M) 3.7 mainshock that occurred at 5:09 am MST on Friday, February 15.  Of the remaining 190 earthquakes, 13 occurred before the M 3.7 and, in retrospect, are considered to be foreshocks.  The largest foreshock, and the only one larger than M 2.0, was an M 3.2 event that occurred seven minutes before the mainshock.   177 of the earthquakes are aftershocks.  The largest aftershock was an M 3.1 event that occurred on Saturday, February 23, at 2:31 am MST.  There have been eleven aftershocks of M 2.0 and larger, including the M 3.1. Only two aftershocks occurred from April 1 through 20.

Was the M 4.0 earthquake that occurred on Wednesday, February 20, near the town of Kanosh in Central Utah related to the recent Bluffdale earthquakes?
No, the February 20 M 4.0 earthquake in central Utah is not related to the Bluffdale earthquakes.  The distance between these areas of recent earthquake activity is more than 120 miles.  The M 3.7 Bluffdale mainshock was too small to trigger other earthquakes at such a large distance.

Are these earthquakes occurring on the Wasatch Fault?
Within the uncertainties in the data, it is possible that the Bluffdale earthquakes are occurring on the nearby Wasatch fault (Figure 3). However, it is also possible that they are occurring on a minor, unnamed fault. It is generally difficult to know for sure which fault an earthquake is on, due to uncertainties in the locations of both faults and earthquakes below the ground surface.  The main exceptions are when an earthquake is large enough for the fault displacement that caused the earthquake to break the ground surface and create a fault scarp.  In Utah, an earthquake usually needs to be larger than M 6.0-6.5 for a surface break to occur.

Do these small earthquakes make a big one less likely?
 No, small earthquakes do not relieve enough stress buildup in the earth to reduce the likelihood of a large earthquake. In fact, every earthquake that occurs has a small, roughly one-in twenty, chance of being a foreshock to a larger earthquake within five days.  A “Larger” earthquake means any earthquake bigger than the one that just occurred, even if it is only 0.1 magnitude units bigger.  The probability of an earthquake being a foreshock to an earthquake that is one or two magnitude units larger is much smaller than one-in-twenty.

Are the recent Blufdale earthquakes unusual?
No, not in the context of statewide earthquake activity.  Small earthquakes occur every day in Utah, although most of them are too small or too far from population centers to be felt.  On the average, the Utah region has one M ≥ 4.0 earthquake per year and one M ≥ 3.0 earthquake per month, not counting foreshocks and aftershocks.  The 2019 Bluffdale earthquakes are within an east-west trending band of seismicity across the southern end of the Salt Lake Valley that has had earthquakes off and on since at least 1971, including events of M 4.1 in 1992 and M 3.2 in 2016 (Figure 3).  The recent earthquakes near Bluffdale serve as a reminder that Utah is earthquake country and a large, damaging earthquake could occur at any time. Therefore, everyone living in Utah should strive to be prepared for large earthquakes.

Historical Seismicity for the Bluffdale, UT area

What can I do to be prepared?
 An excellent source of information on earthquake preparedness is the publication “Putting Down Roots in Earthquake Country”.

Sulphur Peak Earthquake Information

Posted on by Paul Roberson

On September 02, 2017, in eastern ​Idaho ​near ​the ​town of ​Soda Springs a magnitude 5.3 earthquake occurred that was widely felt throughout southeastern Idaho and northern Utah.  This earthquake has been followed by a very active aftershock sequence. These earthquakes are slightly outside of the University of Utah Seismograph Stations area of responsibility, but the area is of interest to UUSS and the USGS Earthquake Hazards Program.

UUSS in partnership with USGS have deployed two UUSS 3-channel strong-motion systems and six USGS 6-channel seismic systems (broadband and strong-motion) within 50 km of the seismicity.

The following page includes information about the earthquake sequence and webicorders for the temporary stations.  We will update the page with more information over time.

Ongoing Yellowstone Earthquake Swarm North of West Yellowstone, MT.

Posted on by Jamie Farrell

August 03, 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 13:00 MDT on August 2nd, 2017, is composed of 1,562 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, 8 earthquakes in the magnitude 3 range, 134 earthquakes in the magnitude 2 range, 505 earthquakes in the magnitude 1 range, 879 earthquakes in the magnitude 0 range, and 35 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 August 3, 2017 at 01:00 PM 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: http://earthquake.usgs.gov/earthquakes/dyfi/.

The April 22, 2017 M 3.8 Earthquake Sequence near Rangely, Colorado

Posted on by Hao Zhang

On April 22, 2017, a magnitude 3.8 earthquake occurred approximately 4 km northwest of Rangely, Colorado at 11:48 AM local time (05:48 PM UTC).  There were 15 felt reports from the town of Rangely, CO.  Two aftershocks, approximately 1 km NNE of the mainshock, were located by UUSS.  The first aftershock (ML 2.6) occurred on April 27 at 03:11 AM local time (09:11 AM UTC), and the second aftershock (ML 3.3) occurred on May 3 at 01:42 AM local time (07:42 AM UTC). Based on the moment tensor solution for the mainshock this was a predominantly strike-slip earthquake on steeply dipping planes with the strike either northwest or northeast.  From the distribution of the aftershock locations, we tentatively favor the northeast striking plane.  Eighteen earthquakes within 20 km of the mainshock , with magnitude greater than 2.0, have been catalogued since 1962.  The largest historical earthquake (ML 4.6, March 20, 1995) was located 2.3 km NE of the 2017 mainshock.

The Rangely area was one of the first focus sites for the study of fluid-induced earthquakes.  Some of the first documented induced earthquakes occurred near Rangely in the 1960s and 1970s.  During this time water-flood expansion was being used for secondary oil recovery.  It was a good place to test the correlation between fluid injection and seismic events with a controlled experiment (Rayleigh et al., 1976), and the experiment showed a direct link.  The seismicity during the experiment occurred on a ENE-WSW trending plane.  This is rotated from the current seismicity, but the locations of the seismic events have also migrated through time.  Water based fluid injection ended in 1983; since 1986 injection of CO2 has been used for secondary oil recovery.

Given the proximity of the recent seismicity to the Rangely Oil Field, it is fair to ask if the recent sequence is also induced.  Analysis of this sequence is ongoing, but initial work includes the following results.  An STA/LTA detector (detection threshold 3.5) was run across continuous waveforms from the two nearest stations (O20A and RDMU) for the time period April 22, 2017–May 04, 2017.  Requiring simultaneous detections on both stations, in order to reduce the number of false detections, resulted in one new detected event that occurred on May 3.  Using cross-correlation, we found similar waveforms (CC > 0.5) from the four events (mainshock, two aftershocks, and the new detected event) recorded at station O20A, suggesting possible common source properties.

The lack of close seismic stations makes it difficult to clearly associate these seismic events with oil production efforts.

Magnitude 4.0 east of Jackson, WY

Posted on by Jamie Farrell

us10004t1f_ciimOn February 26, 2016, an earthquake of magnitude 4.0 struck about 31 km (19 miles) east of Jackson, WY at about 5:00 PM local time.  The quake was reported felt by over 150 people in the Teton region.  There were no reports of any damage.  The earthquake occurred in the Gros Ventre range east of Grand Teton National Park near the location of previous seismic activity.  In 2010 there was a swarm of earthquakes, including a M4.8 earthquake, ~11 km (7 miles) north of this event.Fig04.1_seis_map

 

The Teton region is part of the Intermountain Seismic Belt, a region of relatively high seismicity in the Intermountain West that extends from northern Arizona to western Montana.  Most of the seismicity in the Teton region occurs east of Grand Teton National Park in the Gros Ventre range while there is very little earthquake activity on the Teton Fault.

 

 

 

 

News accounts for this event can be found at the following links:

Jackson Hole News & Guide, February 26, 2016

Casper Star Tribune, February 26, 2016

Jackson Hole News & Guide, February 27, 2016