2020 Magna Earthquake Sequence FAQ

The earthquake map, count, and aftershock plot will be updated on Wednesdays around noon.

Epicenter map for 2020 Magna Earthquake Sequence March 18 - June 24

How many earthquakes have we had in the area?
The University of Utah Seismograph Stations (UUSS) has located 2,320 earthquakes that occurred in the Magna, Utah, area from March 18 through June 24, 11 am MDT (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. The remaining 2,319 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. A M 4.2 aftershocks occurred on April 14 and 17th which were widely felt along the Wastach Front. There have been 40 aftershocks of M 3 and larger. We continue to locate new earthquakes as they occur.

Magnitude vs time plot of Magna Earthquake Sequence, March 18 - June 24

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”.

M4.2 Aftershock, near Magna UT

PRESS RELEASE

University of Utah Seismograph Stations

Released: April 14, 2020 10:15 PM MDT

The University of Utah Seismograph Stations reports that a light earthquake of magnitude 4.2 occurred at 08:56 PM on April 14, 2020 (MDT). The epicenter of the shock was located in the northwestern part of the Salt Lake Valley, 3.3 mi NE of Magna, UT. This earthquake was an aftershock of the magnitude 5.7 earthquake that occurred in the same area on March 18, and was the largest aftershock to occur since the day of the magnitude 5.7 mainshock. Today’s aftershock was widely felt in the Wasatch Front region of Utah, especially in the Salt Lake Valley. To date, the University of Utah Seismograph Stations has located 1,247 aftershocks from the March 18 earthquake, including four others of magnitude 4.0 or larger (all on March 18) and 39 of magnitude 3.0 and larger. The aftershock activity is expected to continue for at least several more weeks, but with the rate continuing to decrease with time.

Anyone who felt the earthquake is encouraged to fill out a survey form on the US Geological Survey website: earthquake.usgs.gov.

Earthquake Summary:

Date (UTC): April 15, 2020 Time (UTC): 02:56

Date (local): April 14, 2020 Time (local): 08:56 PM MDT

Latitude: 40 43.92′ N

Longitude: 112 3.54′ W

Preferred magnitude: 4.2 Ml

Magnitude 5.7 near Magna, UT

PRESS RELEASE

University of Utah Seismograph Stations

Released: March 18, 2020 8:20 AM MDT

The University of Utah Seismograph Stations reports that a moderate
earthquake of magnitude 5.7 occurred at 07:09 AM on March 18, 2020
(MDT). The epicenter of the shock was located in the northwestern
Salt Lake Valley, 3.1 mi N of Magna, UT. This earthquake was widely
felt throughout the Wasatch Front area of north-central Utah. It
has been followed by numerous aftershocks, including 20 of magnitude
3.0 or larger during the first hour after the M 5.7 and two of
magnitude 4.0 or larger. The largest aftershock so far was a M 4.6
event that occurred at 7:14 am.

Today’s earthquake was the largest earthquake to occur in Utah since
a magnitude 5.9 earthquake in 1992 in southwestern Utah near St. George.
Today’s earthquake occurred in a seismically active part of the Salt
Lake Valley, where six magnitude 3.0 or larger earthquakes have
occurred since 1962. The largest of these events was a magnitude 5.2
on September 05, 1962, 0.8 mi NE of Magna, UT.

Anyone who felt the earthquake is encouraged to fill out a survey form
on the US Geological Survey website: earthquake.usgs.gov.

Earthquake Summary:

Date (UTC): March 18, 2020 Time (UTC): 13:09

Date (local): March 18, 2020 Time (local): 07:09 AM MDT

Latitude: 40 45.11′ N

Longitude: 112 4.65′ W

Depth: 10.7 km

Preferred magnitude: 5.7 USGS Mw

Seismograph Technician Opening at UUSS

The University of Utah Seismograph Stations is seeking a specialist who will work under the supervision of other professional staff to operate, repair, and maintain 230 stations forming part of the University of Utah’s regional seismic network. Stations consist of seismic sensors, digital data acquisition systems, and associated telemetry equipment and are sited both in the urban built environment and in remote field locations throughout Utah and in parts of neighboring states. The Seismograph Technician will assist with the installation of new seismograph stations and maintain a detailed record of station visits and a written repair history for specified equipment items.

More information can be found here.

Installed SM instrument in building
Installed Strong-Motion Building Intallation

Magnitude 4 earthquake near Milford, UT

PRESS RELEASE

University of Utah Seismograph Stations

Released: January 16, 2020 08:30 PM MST

The University of Utah Seismograph Stations reports that a light earthquake of magnitude 4.0 occurred at 07:31 PM on January 16, 2020 (MST). The epicenter of the shock was located in southwestern Utah beneath the Mineral Mountains, 10.4 mi SE of the town of Milford, UT and 6 mi NNE of Minersville, UT. The shock was reported felt by residents of Milford and Cedar City as well as other nearby localities. The earthquake was followed by a magnitude 1.5 aftershock that occurred nine minutes later.

Today’s earthquake occurred in a seismically active area of Utah. A total of 17 earthquakes of magnitude 3.0 or greater have occurred within 16 mi of the epicenter of this event since 1962.

The largest of these events was a magnitude 3.9 on April 10, 1998, 1.4mi NNE of Milford, UT.  In 1991 a magnitude 4.6 earthquake occurred 13 miles SE of Minersville.

Anyone who felt the earthquake is encouraged to fill out a survey form on the US Geological Survey website: https://earthquake.usgs.gov/earthquakes/eventpage/uu60356907/tellus.

Earthquake Summary:

Date (UTC):   January 17, 2020         Time (UTC): 02:31

Date (local): January 16, 2020         Time (local): 07:31 PM MST

Latitude:     38 17.50′ N

Longitude:    112 52.43′ W

Preferred magnitude: 4.00 Ml