M 2.7 near Logan, UT

PRESS RELEASE
University of Utah Seismograph Stations
Released: September 19, 2020 10:45 PM MDT

The University of Utah Seismograph Stations reports that an earthquake of magnitude 2.7 occurred at 09:56 PM on September 19, 2020 (MDT). The hypocenter of the shock was located 11 miles beneath Logan Canyon in the Bear River Range,  7 miles east northeast of Logan, UT. 

This earthquake was reported felt by residents of Logan and other cities and towns in the Cache Valley. Today’s earthquake occurred in a seismically active area of Utah. A total of 14 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 4.6 that occurred on March 17, 1966, 14 miles east of Providence, 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):   September 20, 2020         Time (UTC):   03:56
Date (local): September 19, 2020         Time (local): 09:56 PM MDT
Latitude:     41 45.95′ N
Longitude:    111 42.32′ W
Preferred magnitude: 2.7 Ml

2020 Magna Earthquake Sequence FAQ

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

Earthquake Map of 2020 Magna EQ sequence March 18- Sept. 18

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.

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”.

2018 Annual Report

2018 was an especially difficult year because of the unexpected death of Dave Drobeck on February 11. Dave served the University of Utah Seismograph Stations (UUSS) for over 20 years and was instrumental in developing the Yellowstone Seismic Network into one of the premier volcano monitoring networks in the world. Dave’s loss was especially hard on the UUSS engineering group—Corey Hatch, Wes O’keefe, and Jon Rusho—who had to take up extra work duties while grieving the loss of their colleague. A summary of Dave’s career was presented by Bob Smith at a ceremony on February 22, and is reprinted in this report. 

While someone like Dave can never truly be replaced, I am happy to report that a former UUSS undergraduate research assistant, ArvindParapuzha, agreed to return to UUSS as a seismic engineer trainee in May, and that Wes O’keefe worked his first full field season in Yellowstone this past fall. On July 1, long-time seismic analyst Mark Hale was promoted to senior application systems analyst. Congratulations, Mark!

The biggest highlight of 2018 was the June 14 announcement that the University of Utah had been selected to receive a $140 million grant from the Department of Energy to develop the Frontier Observatory for Research in Geothermal Energy (FORGE) site near Milford, Utah. The selection was due in no small part to the effort of UUSS associate director Kris Pankow and her team of students and staff, who created a seismic mitigation plan for the project. Dr. Pankow will continue managing the FORGE seismic risk as work ramps up over the next several years.

We look forward to an exciting new year in 2019. I encourage you to visit our revamped web page at quake.utah.edu to stay up-to-date on our new initiatives and products as well as to find out about the latest seismic activity in Utah. You can also follow UUSS on Twitter with the handle @UUSSQuake.

Best wishes,

Keith D. Koper, UUSS Director