2020 Magna Earthquake Sequence FAQ

Map of epicenters for the Magna Earthquake Sequence March 18-27

How many earthquakes have we had in the area?
The University of Utah Seismograph Stations (UUSS) has located 658 earthquakes that occurred in the Magna, Utah, area from March 18 through March 30, 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 657 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. There have been 33 aftershocks of M 3 and larger. Many (hundreds and perhaps thousands) smaller earthquakes have yet to be located and will be posted in the coming days. We also continue to locate new earthquakes as they occur.

Magnitude vs time plot of Magna Earthquake Sequence, March 18-26

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.

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. 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.

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

Video update about Magnitude 5.7 earthquake in Magna

UUSS Director Keith Koper sat down on Facebook live to explain how the UUSS responds to earthquake events, like the Magnitude 5.7 earthquake in Magna, UT. He also shared important things to know and simple steps to take to be prepared.

Update from the University of Utah Seismograph Stations

Here's an update with our Director Keith Koper on what we're doing and what you can do regarding today's earthquakes.

Posted by University of Utah Seismograph Stations on Wednesday, March 18, 2020

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

COVID-19 UUSS work from home, 24/7 EQ response unaffected

To protect our community during the #COVID crisis: The University of Utah Seismograph Stations offices will be closed. We will continue our regular office hours while working from home, in support of  #SocialDistancing.

Most importantly:
THE 24/7 EMERGENCY EARTHQUAKE RESPONSE WILL BE UNAFFECTED.

Our duty seismologists will have the same response capabilities as before.

For the latest earthquake information: www.quake.utah.edu

For the latest Utah COVID information:

https://coronavirus.utah.gov/

Please do what you can to keep yourselves and the community safe.

Thank you.

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

1992 – St. George, UT – M 5.8

Intermountain Seismic Belt Historical Earthquake Project

September 2, 1992 – St. George, UT – M 5.8

In the early morning of Wednesday, September 2, 1992 (4:26 a.m. MDT), a magnitude 5.8 earthquake occurred near Washington, Utah.

Most of the destruction occurred near the town of Springdale, Utah, near the mouth of Zion National Park. Utah State Route 9 (SR-9) connecting Springdale and the south entrance of Zion Park was closed as a nearby hillside began to slide down over the road. One report estimated that the slide was moving at 3-4 feet per hour. At one point, the slide was measured at two-thirds of a mile long and one-fifth of a mile wide. The slide left a scarp as high as 50 feet in one location.

Three houses on the hillside were destroyed. Residents in one of the homes attempted to evacuate by car but were impeded by rocks and cracks in the road. They left their car and walked/slid down the hillside. Residents of the second house were helped down the hillside by rescue workers. The third house was unoccupied at the time of the earthquake.

The landslide also swept off telephone poles and lines. And a water line broke under the road, near the south entrance to Zion Park. Springdale and Zion Park were without power for about 24 hours. The Park re-opened the next day, but SR-9 remained closed.

The earthquake was reported felt as far west as Las Vegas, Nevada; as far south as Flagstaff, Arizona; as far to the east as Escalante-Boulder, Utah, and as far north as Richfield, Utah.

In the St. George, Utah area, loosened plaster and minor cracks in walls were reported.

In Hurricane, Utah, windows shook, bookcases were knocked over, and goods on store shelves were shaken to floor. The earthquake caused extensive structural damage to an historical house in the city.

In Toquerville, Utah, a building and at least two automobiles were damaged from a large boulder that rolled down a hillside.

There were several reports that loud blasts were heard just prior to the shaking. One Ivins, Utah resident thought that a gas line had exploded. There were also reports of dust clouds from nearby rockslides.

Some liquefaction occurred along the Virgin River as evidenced by small sand boils and ground cracks.

No deaths or serious injuries were reported in connection with this earthquake.


For additional information about this earthquake:

Earthquake Summary 3D Newspaper Articles 3D Photos 3D Blank Thumbnail
Personal Accounts 3D Additional Resources 3D Blank Thumbnail Blank Thumbnail

For more information about this project:

ISB Hist EQ Proj

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.   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

1962 – Magna, UT – M 5.2

Intermountain Seismic Belt Historical Earthquake Project

September 5, 1962 – Magna, UT – M 5.2

A magnitude 5.2 earthquake occurred in Magna, Utah, on Wednesday, September 5, 1962 at 9:04 a.m.

The earthquake was felt from the Ogden, Utah area in the north, down to the Provo/Spanish Fork, Utah area in the south. Widespread structural damage occurred in the Salt Lake Valley, particularly in the northwest.

Structural damage included: shattered windows, collapsed walls or ceilings, cracked foundations, cracked and falling plaster, fallen chimneys, homes shifted on foundations, and dislodged parapet walls. Cracks appeared in houses and buildings throughout the Valley. In downtown Salt Lake City, building damage was mostly limited to cracks in plaster.

Non-structural damage was also widespread and varied: overturned aquariums, store goods fallen from shelves, broken dishes and so forth. There were many reports of stopped clocks.

A number of schools were closed temporarily due to building damage or until inspections could be completed.

Water lines, gas lines and electrical service were not interrupted. One high-pressure gas leak in Davis County, Utah, was repaired after several hours. Telephones remained in service, however, circuits were jammed by calls—some for several hours. There were no reports of damage to roads or rail lines.

No deaths or serious injuries were reported for this earthquake. One person suffered a broken leg after falling on a floor made slippery by contents from broken bottles. Another person sustained a hip injury from slipping as she tried rush from a building.



For additional information about this earthquake:

Earthquake Summary 3D Newspaper Articles 3D Photos 3D Blank Thumbnail
Personal Accounts 3D Additional Resources 3D Blank Thumbnail Blank Thumbnail

For more information about this project:

ISB Hist EQ Proj