2019 Bluffdale Earthquake Sequence FAQ

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”.

M 4.1 near Kanosh, UT

University of Utah Seismograph Stations
Released: April 13, 2019 11:55 PM MDT

The University of Utah Seismograph Stations reports that a light earthquake of magnitude 4.1 occurred at 9:59 PM on April 13, 2019 (MDT).  The epicenter of the shock was located near the Twin Peaks in the southern Sevier Desert, 11 miles east-northeast of the town of Black Rock, UT, and 18 mi west of the town of Kanosh, UT.  Two aftershocks occurred within the first hour after the M 4.1 earthquake, a magnitude 2.7 at 10:09 pm and a magnitude 1.7 at 10:32 pm.   Earlier this year on February 20, a magnitude 4.0 earthquake occurred 15 miles east of today’s earthquake and 5.5 miles south-southwest of Kanosh.  A total of 18 earthquakes of magnitude 3.0 to 4.0 have occurred within 16 miles of the epicenter of today’s event since 1962.

Anyone who felt the earthquake is encouraged to fill out a survey form on the US Geological Survey “Did You Feet it?” website.

M 2.4 felt near Saratoga Springs, UT

PRESS RELEASE

University of Utah Seismograph Stations
Released: April 10, 2019 09:45 PM MDT

The University of Utah Seismograph Stations reports that an earthquake of magnitude 2.4 occurred at 08:06 PM on April 10, 2019 (MDT). The epicenter of the shock was located beneath the city of Saratoga Springs, Utah, along the northwestern shore of Utah Lake. This earthquake was reported felt in the northern Utah Valley cities of Saratoga Springs, Lehi, and Eagle Mountain. A total of 8 earthquakes of magnitude 3.0 or greater have occurred within 16 miles of the epicenter of this event since 1962. Earthquakes the size of today’s event or larger occur on the average of once per week somewhere in the Utah region.

Anyone who felt the earthquake is encouraged to fill out a survey form on the US Geological Survey “Did You Feet it?” website.

M 4.0 Near Kanosh, UT

PRESS RELEASE

University of Utah Seismograph Stations

Released: February 20, 2019 01:45 AM MST

The University of Utah Seismograph Stations reports that a light earthquake of magnitude 4.0 occurred at 12:05 AM on February 20, 2019(MST). The epicenter of the shock was located in central Utah in the southwestern part of the Pavant Range, 5.3 mi south-southwest of the town of Kanosh, UT, and 18 miles southwest of the city of Fillmore. This earthquake was reported felt in the cities of Fillmore, Monroe, and Richfield, Utah. Three small aftershocks occurred within the first 45 minutes after the mainshock, all of magnitude less than 2.0.

A magnitude 3.3 earthquake occurred in the same area last Saturday
at 3:05 pm MST. A total of 28 earthquakes of magnitude 3.0 or greater have occurred within 16 miles of the epicenter of today’s event since 1962. The largest of these earthquakes was a magnitude 4.0 on February 23, 2001, located 8.2 mi southwest of Kanosh. In 1967, a magnitude 5.2 earthquake occurred 23 miles to the southeast of today’s event.

Anyone who felt the earthquake is encouraged to fill out a survey form on the US Geological Survey “Did You Feet it?” website.

M 3.7 near Blufdale, UT

PRESS RELEASE

University of Utah Seismograph Stations Released: February 15, 2019 06:45 AM MST

The University of Utah Seismograph Stations reports that a minor earthquake of magnitude 3.7 occurred at 5:09 AM on February 15, 2019 (MST).  The epicenter of the shock was located at the southern end of the Salt Lake Valley, 1.8 miles south of the town of Bluffdale, UT.

This earthquake was preceded by a magnitude 3.2 foreshock at 5:02 am and was followed by six aftershocks, all smaller than magnitude 2.

This morning’s earthquake was reported felt by more than 7,000 residents of the Salt Lake Valley and Utah Valley.  The foreshock was also reported felt.  Since 1962, five earthquakes of magnitude 3.0 or greater have occurred within 16 miles of the epicenter of today’s event.  The largest of these events was a magnitude 4.1 on March 16, 1992, located six miles west-southwest of Bluffdale, UT.

Anyone who felt the earthquake is encouraged to fill out a survey form on the US Geological Survey “Did You Feet it?” website.

Magnitude 3.8 near Enterprise, UT

Press Release

Released: January 16, 2019 03:30 PM MST

The University of Utah Seismograph Stations reports that a minor earthquake of magnitude 3.8 occurred at 03:00 PM on January 16, 2019 (MST).  The epicenter of the shock was located in southwestern Utah, 1.4 miles south of Upper Enterprise Reservoir and 10 miles SW of the town of Enterprise, UT.  A magnitude 2.8 foreshock occurred two minutes before the magnitude 3.8 earthquake.  Ten other earthquakes have occurred in this same area during the past week, ranging in magnitude from 0.8 to 2.9.  Earthquake activity in this area is not unusual.  A total of 11 earthquakes of magnitude 3.0 or greater have occurred since 1962 within 16 miles of today’s earthquakes.  The largest of these events was a magnitude 4.3 on January 15, 2016, located 12 miles WSW of the town of Enterprise.

Today’s M 3.8 earthquake was reported felt in the town of Central, UT, 14 miles NE of the epicenter, and in the town of Ivins. UT. Anyone who felt the earthquake is encouraged to fill out a survey form on the US Geological Survey “Did You Feet it?” website.

M 2.8 Near Bountiful, UT Felt Along Wasatch Front

Press Release

Released: October 23, 2018 11:45 PM MDT

The University of Utah Seismograph Stations reports that an earthquake of magnitude 2.8 occurred at 10:30 PM on October 23, 2018 (MDT). The epicenter of the shock was located beneath the Wasatch Range, 11 miles east of the city of Bountiful, UT, and 12 miles south of the city of Morgan, UT. This earthquake was reported felt by residents of Wasatch Front communities extending from Salt Lake City on the south to Kayesville on the north, with most of the reports coming from the cities of Bountiful, Centerville, and Farmington.

A total of 5 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 3.3 on June 11, 2014, 10 miles east of Centerville, UT.

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

M 3.8 near Cove Fort, Utah

Press Release

Released: September 12, 2018 12:50 AM MDT

The University of Utah Seismograph Stations reports that a small earthquake of magnitude 3.8 occurred at 11:34 PM on September 11, 2018 (MDT).  The epicenter of the shock was located in southwestern Utah in the southern Sevier Desert,  15 miles west-northwest of Cove Fort, UT.  This earthquake was followed by at least four aftershocks in the first hour, the largest of magnitude 2.3.  A total of 19 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 4.0 on February 23, 2001, 8 miles southwest of Kanosh, UT.

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

Earthquake database for Utah Geological Survey Map 277: Utah earthquakes (1850–2016) and Quaternary faults: Utah Geological Survey Open-File Report 667

The Utah Geological Survey (UGS), University of Utah Seismograph Stations (UUSS), and Utah Division of Emergency Management (UDEM) recently published the Utah Earthquakes (1850–2016) and Quaternary Fault Map (UGS Map 277). The new map shows earthquakes within and surrounding Utah from 1850 to 2016, and faults considered to be sources of large earthquakes.

Utah Earthquakes (1850-2016) and Quaternary Faults

 

The faults shown on the map are considered geologically active, have been sources of large earthquakes (about magnitude 6.5 and greater) during the Quaternary Period (past 2.6 million years), and are the most likely sources of large earthquakes in the future. Most of the small to moderate-sized earthquakes on the map are “background” earthquakes not readily associated with known faults and too small to have triggered surface faulting (under about magnitude 6.5).

 

There is a 57% probability (over 1 in 2 chance) that a magnitude 6.0 or greater earthquake will occur in the Wasatch Front region in the next 50 years. To address this threat, the Utah Earthquake Program, consisting of the UGS, UUSS, and the UDEM, developed the map so the public could more fully understand the hazard from earthquakes and faults, as well as the resulting risk to property, infrastructure, and life safety in Utah. Users of the map will be able to determine past earthquake locations and relative magnitudes (size), along with the locations of active faults and the timing of their most recent movement.

 

Printed copies of the map are available for $15 at the Utah Department of Natural Resources Map & Bookstore. The map is also available as a PDF download at https://ugspub.nr.utah.gov/publications/maps/m-277.pdf (44 by 62 inches in size) and can be printed on a wide-format printer.

The database for the seismicity plotted on the map, together with explanatory information, is provided in a companion report:
Arabasz, W. J., Burlacu, R., and Pechmann, J. C., 2017, Earthquake database for Utah Geological Survey Map 277: Utah earthquakes (1850–2016) and Quaternary faults: Utah Geological Survey Open-File Report 667, 12 p. plus 4 electronic supplements, available as a PDF download.
The electronic supplements include the data for the seismic events plotted on the map, which are listed in two separate catalogs, each in the form of a Microsoft Excel workbook and an ArcGIS feature class within a file geodatabase. The catalog files are available for download.

Magnitude 3.4 earthquake near Monroe, UT

PRESS RELEASE

University of Utah Seismograph Stations

Released: September 24, 2017 1:00 PM MDT

The University of Utah Seismograph Stations reports that a minor earthquake of magnitude 3.4 occurred at 10:38 PM on Saturday,
September 23, 2017 (MDT), in southern Utah. The shock was located beneath the Sevier Plateau, 6 km ( 4 mi) east-southeast of the town
of Monroe, UT, and 18 km (11 mi) south of the town of Richfield, UT. The earthquake was reported felt in the towns of Monroe, Richfield,
and Joseph, Utah. It was followed by two small aftershocks, one of M 1.7 at 10:46 pm on Saturday night and the other of M 1.6 at 09:43
on Sunday morning.

Yesterday evening’s earthquake occurred within a seismically active area of Utah A total of 23 earthquakes of magnitude 3.0 or greater
have occurred within 25 km (16 mi) of the epicenter of this event since 1962. The largest of these events was a magnitude 5.2 on
October 04, 1967, 10.1km ( 6.3 mi) ESE of Sevier, UT.

Anyone who felt the earthquake is encouraged to fill out a survey form either on the Seismograph Stations website: www.quake.utah.edu or the
US Geological Survey website: earthquake.usgs.gov.

Earthquake Summary:

Date (UTC): September 24, 2017 Time (UTC): 04:38

Date (local): September 23, 2017 Time (local): 10:38 PM MDT

Latitude: 38 36.39′ N

Longitude: 112 3.43′ W

Preferred magnitude: 3.4 Ml