1943 – Magna, UT – M 5.0

Intermountain Seismic Belt Historical Earthquake Project

February 22, 1943 – Magna, UT – M 5.0

At 8:20 a.m. (local time) on Monday, February 22, 1943, a magnitude 5.0 earthquake occurred near Magna, Utah. It was most strongly felt in Magna and the surrounding Salt Lake Valley. The earthquake was also reported felt in nearby Utah communities of Ogden, Bingham, Tooele and Provo.

Individuals in Bingham initially thought that the shaking was due to a mine blast. Others feared that additional, stronger earthquakes might follow. No injuries from the earthquake were reported.

There were reports from downtown Salt Lake City that buildings swayed slightly, and clocks stopped. Dishes and windows rattled. Merchandise fell from store shelves. A chimney fell at an Air Force training center in Kearns, Utah and there were reports of cracks in buildings. Some people believed that the earthquake caused damage that resulted in roof leaks at the Salt Lake City and County building.

On the day of the Magna earthquake, five people were reportedly killed in an unrelated earthquake off the coast of Mexico, 250 miles southwest of Mexico City.

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2017 Annual Report

2017 Annual Report Cover Page

2017 Annual Report

I am happy to report the University of Utah Seismograph Sta- tions (UUSS) had another exciting and productive year in 2017. Thanks to all of you who support and promote our mission of reducing the risk of earthquakes in Utah through research, edu- cation, and public service.

An Mw 5.3 earthquake on Sept. 2, 2017, in southeastern Idaho reminded us that we absolutely do live in earthquake country. Thankfully, this earthquake caused little damage, but its shaking was felt throughout northern Utah, as far south as Provo. UUSS responded to the earthquake by partnering with the U.S. Geo- logical Survey and the Idaho Geological Survey to deploy a tem- porary array of seismographs in the source region. Using these data, we detected and located over 1,000 aftershocks in the two months following the mainshock. This allowed us to map out a previously unknown fault system.

UUSS also recorded enhanced seismicity in Yellowstone Na- tional Park during 2017. Between June 12 and Sept. 30, a swarm of over 2,400 earthquakes was recorded in the Maple Creek re- gion of Yellowstone. The largest event in the swarm was an Mw 4.4 earthquake on June 15 that was widely felt throughout the park. Although earthquake swarms in Yellowstone are common, this was the second longest swarm ever recorded. Yellowstone earthquake swarms are often related to the movement of fluids in the crust and usually do not portend a volcanic eruption; howev- er, it remains important to monitor them closely.

In 2017, UUSS continued working with the University of Utah team vying to host the Frontier Observatory for Research in Geo- thermal Energy (FORGE). This project is sponsored by the U. S. Dept. of Energy and aims to build a facility for developing tech- nologies related to enhanced geothermal energy production. The UUSS FORGE effort is led by Prof. Kris Pankow and is focused on quantifying the seismic hazard near the proposed FORGE site in Milford, Utah. Utah is one of two finalists for this project, and the winner will be announced in 2018.

We look forward to another exciting year in 2018. I encourage you to visit our web page at quake.utah.edu to stay up-to-date on our initiatives and products as well as to find out about the lat- est seismic activity in Utah and Yellowstone. You can also follow UUSS on Twitter with the handle @UUSSquake.

Best wishes, Keith D. Koper

1959 – Hebgen Lake, MT – M 7.5

Intermountain Seismic Belt Historical Earthquake Project

August 17, 1959 – Hebgen Lake, MT – M 7.5

The Hebgen Lake earthquake—the largest and deadliest earthquake recorded in Montana and the Intermountain West—occurred at 11:37 p.m. (local time) on Monday, August 17, 1959. The epicenter of the magnitude 7.5 earthquake was approximately 15 miles north of West Yellowstone, Montana (later revised by the U.S. Geological Survey to magnitude 7.3 and located 6.5 miles northwest of West Yellowstone). The earthquake was reported felt as far north as Banff, Canada; as far south as Provo, Utah; as far east as Dickinson, North Dakota; and as far west as Seattle, Washington (Stover and Coffman, 1993). Seven significant aftershocks ranging in magnitude from 5½ to 6½ occurred in the three months following the mainshock.

The greatest number of reported injuries and deaths occurred in the Madison River Canyon where the earthquake triggered an 85-million-ton landslide on a mountain five miles west of Hebgen Lake. The landslide roared down over a popular recreation area where an estimated 200 people were camping. The earthquake also caused a northward tilt of the Hebgen Lake bed. This triggered a reported 20-foot wall of water that overtopped Hebgen Dam followed by several 3-4 foot surges. Eyewitnesses reported seeing camping trailers swept down into the Madison River, cars and their occupants buried in dirt and rock, and trees flying through the air. There were reports of screams and cries for help. Twenty-eight individuals died from their injuries or were presumed buried in the slide.

The landslide dammed the Madison River, creating what became known as “Quake Lake.” Montana Highway 287, the primary route through the Madison River Canyon, was rendered impassable due to slide debris, fault scarps (as high as 18 feet) and sections of the highway that fell into Hebgen Lake.

Emergency responders parachuted into the area to establish communication and to provide first-aid. The injured were evacuated by helicopter to an aid station in West Yellowstone and then on to nearby hospitals by airplane. Deceased were airlifted to a morgue in the town of Ennis, Montana. Remaining survivors were able to evacuate later on roads that had been cleared or newly constructed.

According to one report, the ground shaking produced sixteen cracks in the Hebgen Dam. In spite of the damage it was determined the dam would hold. However, precautions were taken to evacuate the town of Ennis 45 miles away and to warn residents in the Madison Valley. The Army Corps of Engineers moved quickly to construct a spillway at Quake Lake before the rising waters topped the landslide dam. Additional earthquake tremors slowed work on roads and dams as well as search and rescue efforts.

When it was determined that no other victims would be recovered from the landslide, a brief memorial service was held near the mouth of the Madison River Canyon. Officiators from several denominations led the group of approximately 50 attendees in prayer. They also consecrated the slide as the final resting place for those who had perished.

The West entrance to Yellowstone National Park was closed with no travel possible along the park’s west side due to landslides, rockfalls and bridge damage. One individual in West Yellowstone at the time of the earthquake reported hearing an awful roar, felt his cabin shaking and lost electrical power. No buildings collapsed but many were severely cracked or damaged. Thousands of frightened tourists left the park, while curious onlookers arrived to survey the damage.

In Billings, Montana, the earthquake awakened hundreds of residents who reported swinging light fixtures, rattling dishes, rolling beds, swinging doors and shaking houses. One person reported that his swimming pool completely overflowed onto the patio.

In Bozeman, Montana, damage included downed chimney tops and store merchandise shaken from shelves.

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1942 (Sep) – Cedar City, UT – M 5

Intermountain Seismic Belt Historical Earthquake Project

September 26, 1942 – Cedar City, UT – M 5

On September 26, 1942, Cedar City, Utah experienced it’s second magnitude 5 earthquake in less than a month. The earthquake occurred early Saturday morning at 7:50 a.m. (local time).

There were reports of loosened chimney bricks at some homes as well as cracked plaster and walls. The earthquake also cracked a plate glass window at a city market.

The earthquake was reported felt by residents within approximately a 10-mile radius of the city. Workers at the Columbia Iron Mine located 20 miles west of Cedar City also reported feeling the earthquake.

No injuries or deaths were reported.

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1942 (Aug) – Cedar City, UT – M 5

Intermountain Seismic Belt Historical Earthquake Project

August 30, 1942 – Cedar City, UT – M 5

On August 30, 1942 at 3:08 p.m. (local time) a magnitude 5.0 earthquake struck Cedar City, Utah. It was reported that the earthquake was accompanied by a loud rumbling sound. There were no reports of the earthquake being felt outside the city. The earthquake startled residents and some fled from buildings but there were no reported injuries. Reported damage was limited to bricks dislodged from chimneys.

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1925 – Clarkston Valley, MT – M 6¾

Intermountain Seismic Belt Historical Earthquake Project

June 27, 1925 – Clarkston Valley, MT – 

The Clarkston Valley, Montana earthquake occurred at 6:21 p.m. local time on June 27, 1925. The epicenter was located approximately 8 miles north of Three Forks, MT just north of Yellowstone Park. It was reported felt over nearly two-thirds of the state (approximately 1,000,000 square kilometers) – as far west as Seattle, WA to the eastern Montana/South Dakota border, as far north as Thermopolis and Casper, WY and south to Spokane, WA.

Some buildings in areas near the epicenter were badly damaged. Buildings and pavement were cracked. Chimneys toppled. Windows shattered in some locations. Plaster was shaken from walls and merchandise fell from store shelves.

The heaviest damage in terms of quantity and severity was reported in Three Forks, Manhattan and White Sulphur Springs with some buildings being reduced to rubble. There were also reports of extensive damage to the town of Willow Creek, including reports that the town was in flames. Broken wire connections prevented communication to confirm these reports. It was later learned that damage in Willow Creek was slight.

Some individuals rushed into the streets, fainted or were knocked to the ground from the shaking, but no loss of life was reported. A woman sustained a broken leg (also reported as a broken hip) as she fell while rushing out of her home. Additional reported injuries were limited to bruises and cuts due to broken glass and falling materials. Many individuals were too nervous to sleep and some preferred to sleep out of doors.

The earthquake triggered several landslides and rockslides. Three passenger trains were stranded when rockslides blocked rail lines. There were also reports of rail tunnels caving in. And some concern was reported about the safety of area bridges. A number of ground cracks and fissures were reported in areas closest to the epicenter. There were also reports of increased flow at some springs in the area.

It was reported that the day following the earthquake, thousands of visitors from nearby towns and cities flooded into Manhattan and Three Forks to survey the damage.

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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


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.

1935 – Helena, MT (series) – M 6¼

Intermountain Seismic Belt Historical Earthquake Project

October 18, 1935 – Helena, MT (series) – M 6¼

October 12, 1935 – Foreshock (M 5.9)

This early morning earthquake (12:50 a.m. local time) caused many frightened residents to run from their homes. It was reported that despite the alarm people felt, many maintained a sense of humor about the event as they gathered in the streets and swapped stories of their experiences. No deaths resulting from the foreshock were reported.

Reports described damage as severe and widespread throughout the city. Windows were broken, stock was shaken from store shelves, pipes and wires were broken, chimneys toppled, furniture overturned, walls were cracked and plaster was shaken from walls and ceilings. It was reported that City Engineer Oscar Baarson estimated total damages between $50,000 and $75,000.

Following the foreshock, two officials advised taking measures to make buildings more earthquake resistant. Suggested measures included bracing chimneys, deeper foundations especially on loose soils, fastening brick veneers to walls, discontinuing the use of veneers altogether. Other suggestions included revising the building codes to make structures more earthquake resistant.

The earthquake was reported felt in Great Falls, Butte and Dillon, MT. Additional smaller earthquakes continued to be felt. In a news article published on October 17 it was reported that the Helena Weather Bureau had recorded a total of 52 earthquakes as of October 16 with the latest two quakes being 12 hours and 45 minutes apart. The article concluded that, “The fact that the quivers are so far apart indicates that the ‘earthquake season’ is drawing to a conclusion.”

October 18, 1935 – Main Shock (M 6¼)

At 9:48 p.m. (local time) the city was rocked by the magnitude 6¼ main shock. Some individuals screamed and ran from buildings. One person was reported killed when he was crushed under a brick wall that fell into the street. Another died from injuries sustained from a building collapse. A score or more individuals were seriously injured, most from being struck by falling debris as they ran out of buildings. As terrified people fled the city by car, a number of automobile accidents occurred resulting in additional injuries.

The earthquake knocked out lights and power for approximately an hour causing further terror, and difficulty for doctors attempting to treat the injured.

Significant damage occurred to many buildings with some entirely destroyed. Approximately 300 homes were damaged so badly as to be uninhabitable. One report described the streets being strewn with debris. Telephone service was interrupted for more than two hours.

City Engineer Oscar Baarson estimated damages from the earthquake at a minimum of $2,500,000. A report on October 21 indicated that Mr. Baarson requested patience as he and a crew of seven worked their way through several hundred requests for damage inspections.

The American Red Cross, Federal Emergency Relief Administration (FERA) and National Guard, assisted in providing first aid stations, sleeping quarters and kitchens for the hundreds of people rendered homeless by the earthquake. The local Y.M.C.A. invited homeless individuals to shower at their facilities for no cost. Authorities estimated it would be a week before people were allowed to resume normal affairs in the city.

The Red Cross reported 100 requests (representing approximately 400 individuals) for emergency food and medical care. The Red Cross also prepared to assist with a home rebuilding program for families in need. Local banks pledged resources for making home repair loans as approved by the Federal Housing Administration.

Surface cracks 150 feet long, three feet deep and several inches wide were reported at one location in the Helena Valley.

The earthquake was reported felt over a wide area of western Montana, but no damage outside the city of Helena was reported. Additional felt reports were received from Washington and Idaho.

October 31, 1935 – Aftershock (M 6)

At 11:37 a.m. (local time) a significant aftershock occurred near East Helena, MT. One report noted that the shock surprised Helena residents, who had believed the worst of the shaking had occurred earlier in the month. The report also noted that aside from some fainting spells, little panic was observed. However, some individuals evacuated the city by car.

Cracked plaster and broken windows were reported. Two school buildings suffered significant damage. On the west side of the city, there were reports of fallen chimneys. However, on Helena’s east side, some buildings that had been only partly damaged by the main shock were completely destroyed when the aftershock occurred. It appeared that most of the damage was to structures already weakened by the main shock. Damage to buildings that had been unaffected by the main shock consisted mostly of cracks in plaster and exterior walls and damaged chimneys.

Two brick masons, part of a crew from Salt Lake City, were killed from falling bricks as they were removing a smokestack at the local brewery. There were at least nine individuals who suffered serious injuries during the aftershock.

The north wing of the new Helena High School, already badly damaged from the main shock, completely collapsed during the October 31 aftershock. It was reported that 25-30 men who were working in the building escaped without injury thanks in part, to their foreman who shouted reminders for them not to run out of the structure.

Plans to open city schools following the main shock were cancelled when the aftershock occurred. It was later decided that schools would not open until after the new year.

November 28, 1935 – Aftershock (M 5.5)

Less than a month later, the city experienced another significant aftershock that struck at 7:41 a.m. (local time). The earthquake did not cause significant new damage in the city of Helena. It was, however, reported to be among the strongest of the series felt outside the area in locations such as Great Falls, Butte, Missoula, Kalispell and Deer Lodge among others. Bozeman reported only light shaking.

Following the earthquake, City Engineer Oscar Baarson revised his estimate of total damages from the earthquake series to $5,000,000.00 or more.

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