SALT LAKE CITY (ABC4) –A few days after the coronavirus locked down most people in Utah, another reality shock hit. At 7:09 on March 18, 2020, a 5.7 magnitude earthquake shook the Salt Lake Valley.
For Salt Lake City, it was the first major earthquake since the city was founded.
Moderate by geological standards, it didn’t feel moderate to everyone whose lives had just been changed by the oncoming pandemic.
It almost felt, apocalyptic.
The quake was Utah’s strongest since a 1992 earthquake in St. George. The earthquake’s epicenter was 8 miles below Magna, and people felt it along the Wasatch Front, into Colorado, Wyoming, and Idaho.
According to the Utah Geological Survey and University of Utah Seismic Stations, “No major injuries were reported from the mainshock or aftershocks. Damage occurred throughout the valley with the most severe damage in Magna.”
After the initial tremors, the clock was ticking as first responders, and emergency teams sprung into action across the valley. Because of the coordinated response and modern technology, the earthquake made history as one of the best-documented in the entire Basin and Range area.
“The Magna earthquake sequence is one of the best-recorded earthquake sequences in the entire Basin and Range province,” said Keith Koper, director of UUSS and chair of the Utah Seismic Safety Commission (USSC). “Our network of permanent and temporary seismometers created a wealth of data that led to several research opportunities both published and ongoing. This research has impacted our understanding about faults, earthquakes, and seismic hazard in Utah and the Intermountain West.”
Within two hours the Utah Geological Survey (UGS) had their own Emergency Operation Center active where scientific information could be coordinated.
To get an idea of how fast the information was moving, the USGS reports, “Various organizations contributed to the Magna earthquake clearinghouse, including the UGS, Salt Lake County, the UUSS, the USGS, the Utah Department of Transportation (UDOT), the Earthquake Engineering Research Institute (EERI), UNAVCO, the Utah State Historic Preservation Office, UDEM, Utah State University, Utah Valley University, the Natural History Museum of Utah, Stanford Research Computing Center, the Utah Geological Association, Granite School District, StrongMotions Inc., Geohazards TEP, Poll Sound, and Salt Lake City. Additionally, we began a public outreach campaign through social media to encourage impacted citizens to share their photographs and videos. Seventeen people responded and contributed 50 photographs and 15 videos.”
UGS sent field reconnaissance teams to provide science assistance to the emergency responders.
The agency also provided a digital web-based data clearinghouse. According to the USGS, “Clearinghouse data are also critical to the performance evaluation of infrastructure during earthquakes, including the effectiveness of building codes, material types, and construction methods. These evaluations can reduce the impact and effects of future earthquakes.”
Members of the Utah Geological Survey response team and one from the Utah Seismology Lab started what would be a crazy day without knowing what happened at the moment.
“The really interesting thing,” says University of Utah Seismologist Katherine Whidden, “is this was the second day of us working remotely, so we did our entire earthquake response, with everybody working from home, a few people did go into the office, but most of us were working remotely from home. I was living in an RV at the time, my husband and I took some time off…we were back in Salt Lake when the earthquake happened.”
“I didn’t feel the shaking actually because I was in my car,” says Utah Geological Survey Project Geologist, Geologic Hazards Program, Emily Kleber. “I drove to the grocery store so I could get supplies. I remember driving in my car, seeing a couple of flashes which were transformers blowing up, and then getting to the downtown Sprouts, and everyone was standing outside; they were all very, very shaken.”
Geologist Adam Hiscock also a Project Geologist, Geologic Hazards Program with UGS, says, “Unlike Emily I am not much of a morning person, I was still in bed and my wife she woke up and said, “Oh, it’s an earthquake, Adam, get under something.” by the time I had gotten up and got clothes on the shaking had pretty much stopped by then.”
Both Geologists packed snacks and got ready for a long day. After the two arrived at work, they were dispatched out to help first responders in the field.
Hiscock noticed all the people could not pump gas because the power was out in West Valley City.
“We were the field team,” says Kleber, “kind of the boots on the ground, starting to do reconnaissance of certain areas, we thought something geologically might have happened.”
Hiscock adds, “We knew it was a moderate magnitude earthquake, we did not know what to expect but we knew there wouldn’t be widespread surface effects from an earthquake that size.”
The search started for effects, top of mind for the geologists were liquefaction events.
“We started our recon by focusing on liquefaction and those types of effects.”
Kleber explains, “It happened in spring, the beginning of runoff, we expect to see the liquefaction where there are layers of sand below the surface and in the Salt Lake Valley, we have thousands of feet of just sand before you get to hard bedrock. You would expect to see liquefaction where the water table is high, an area where the surface water collects…we had those kinds of conditions working against us.”
Liquefaction is a scary term for a lot of Utahns, an urban legend says in a big earthquake the entire Salt Lake Valley would experience liquefaction, this is a myth.
“It’s definitely a myth” says USG’s Kleber, “We would not expect to see widespread liquefaction throughout the whole valley, it’s not going to turn into a lake, but we definitely have evidence that certain areas would experience liquefaction.”
According to the Utah seismograph stations, there were 20 aftershocks in the first hour after the quake.
Kleber says that on a geologic time scale, “this was a moderate event, but for people, this was a major event in their lives…to us scientifically it wasn’t the big one, in terms of us as humans living in this valley together. Personally, I hope this is the only earthquake I ever respond to. I don’t need anything bigger.”
Whidden adds, “One thing that was interesting about the day, we were planning where to put “U” stations when a big event happens we usually put out temporary stations, that are optimally located so we can record all the really small aftershocks.”
UDOT reported the day after there had been two liquefaction events, teams rushed out to look.
Using drones, the teams discovered there had been liquefaction near Saltair. The drone discovered “sand boils” underwater, which were more numerous than those on the land. The boils were observed at other ponds.
“When you see the sand boils, and you look, you can see little holes; that’s how the sand kind of just blobs onto the surface,” says Kebler. “We saw a lot of them, but they were in the retaining ponds of the interchange, so not necessarily a natural geologic environment.”
The team also discovered cracks on the interchange.
Kleber says we are at the very edge of the basin and range, “To the east of us is the Colorado plateau which is this big honking piece of stable crust, and the basin and range to the west of us is where the crust is thinning. The earth’s crust is very dynamic; not all the fun is happening at the plate boundaries.”
She continues, “We have this big sediment pile in the Salt Lake Valley related to the Lake Bonneville cycle when sand shakes under the subsurface, sedimentary environments for 25,000 years or so, what happens is you have that saturated sand, and as it’s shaken it loses its strength if you pick up sand and shake it in your hand essentially it turns to liquid, when that happens below the surface it kind of loses space, it’s that conservation of space idea, sand will liquefy under the subsurface and kind of erupt over the tops, on the surface and just deposit onto the surface.”
Hiscock says the mean slip rate of the Wasatch front is 1.3 millimeters per year; San Andreas is a much higher slip rate in California. Kleber adds the number is an approximate value “averaged over tens of thousands of years when there’s an earthquake the valley’s get a little bit lower, and the mountains get a little bit higher.”
A year after the earthquake, what has been learned about the Wasatch Front? According to the state agencies, “Prior to the Magna earthquake, the exact location of the Wasatch fault was unknown, but many scientists thought it dipped at a steep angle deep beneath the Salt Lake Valley. Based on data from the Magna sequence, several research papers now suggest the sequence actually occurred on the Salt Lake City segment of the Wasatch fault. Evidence also suggests that the fault curves to a shallower angle and is not as deep beneath the surface as previously thought.”
Which means the Wasatch Front kind of curves like a scoop.
“Whidden says, “It was a shocking event to us because we don’t feel earthquakes like this a whole lot, but it was not unusual tectonically speaking.”
So what was learned by the seismologists and geologists in the last year? They all say be prepared.
Whidden explains, “This magnitude 5.7 was a good reminder we live in earthquake country, and we can have a large damaging earthquake at any time, this event was great because we all got a good shake, we got a good scare, I know I did, but no one was really hurt, and the damage was not severe, but, we got a really good reminder this can happen here, and the best thing we can do is be prepared.”
“It was pretty clear that a lot of people learned about aftershocks, and that they tend to happen after larger earthquakes” adds Kleber, “If we thought we were prepared before, we need to prepare again and more, and often. The key is if you make a plan you’re not only going to increase your chances of surviving but thriving after an earthquake and being able to help your neighbors and your family.”
The geologist says, “This was the red flag, the wake-up call, it’s time to make a plan with your family.”
1 year later the Magna Earthquake is still ongoing, but has seen a decrease in activity over the last 12 months.
Over 2,590 aftershocks have been felt over the last year.