Main Navigation

Home U Rising Here’s what the new earthquake maps show for Utah and the U.S.


Scientists have been forecasting a big earthquake in Utah for decades and newly released earthquake maps provide an update on our risk. Seismologist Jim Pechmann, a research associate professor emeritus in the Department of Geology and Geophysics, shares insights about the new maps and what it could mean for Utah in this episode of U Rising hosted by Julie Kiefer.

Subscribe to the U Rising podcast on your favorite streaming platform, including Apple Podcasts, Spotify and Google Podcasts. You can also access episodes of U Rising on our news website, linked here.


Julie Kiefer: If you've lived in Utah for any length of time, you've probably heard this is earthquake country. Scientists have been forecasting a big one in Utah for decades, and a newly released earthquake map provides an update on our risk.

I'm Julie Kiefer, associate director of science communications at University of Utah Health, and my guest today is Jim Pechmann.

He's a seismologist and research associate professor emeritus in the Department of Geology and Geophysics. Jim is going to share insights about a new earthquake map issued by the U.S. Geological Survey, and it'll help us understand what it could mean for us here in Utah.

Welcome to U Rising, Jim!

Jim Pechmann: Thank you and thank you for having me.

Julie Kiefer: So, the U.S. Geological Survey, or USGS, released a new map a few weeks ago that shows where damaging earthquakes are most likely to occur in the country. And if you look at this map, it's splotchy, there's red, there's green, there's blue. And looking at Utah in particular, about half of the state is yellow, including in and around Salt Lake City. So, tell me, what are we looking at and what does it mean for Utah?

Jim Pechmann: Okay, so the map that you are referring to is a color-coded map of the U.S. showing the chance of damaging ground shaking from earthquakes over the next 100 years. On this map, it looks like about half of Utah is yellow or orange. The yellow indicates a 20 to 50 percent probability of a damaging earthquake, and the orange indicates a 50 to 75 percent probability of a damaging earthquake over the next 100 years.

So, it's important to note that most of the orange is in the Wasatch Front region where 80 percent of the people in Utah live. The rest of the orange is mostly along the I-15 corridor through central and southwestern Utah. The eastern and southernmost part of the state is green on this map, which indicates the 5 to 25 percent chance of a damaging earthquake in the next 100 years—not zero.

So, the message of this map is that damaging earthquakes can occur pretty much anywhere in Utah, however, they're most likely to occur in the Wasatch Front region and elsewhere along the I-15 corridor.

Julie Kiefer: And so probably a lot of our listeners are residents of Utah. I mean, how can we think about this in practical terms? I suppose if we look at California, which is really red, at least we know we're not in as much risk as that state, but does this say anything about the big one and the chances of that happening?

Jim Pechmann: Indirectly it does, in that this map just shows the probability of damaging ground motion, which can be slight or catastrophic. So, this is just one of many maps that the USGS put out. It's one of the easiest ones to explain though.

Julie Kiefer: So, the last big earthquake in Utah was in 2020 in Magna, which is not that far from Salt Lake City. I think that hit at about a 5.7 and that was a really scary time for a lot of people. It was so unexpected. First of all, I'm wondering what your reaction was when would you felt that earthquake?

Jim Pechmann: What my reaction was? Well, I was still asleep, and so it took me a little while to figure out what was really going on because it first just sounded like a really strong gust of wind. But then I realized, no, that's not just the wind, that's an earthquake. And then I could see things moving in the room and I got up and went into the study and stayed there pretty much all day online.

Julie Kiefer: And is this an earthquake that you studied? What have we learned from that earthquake?

Jim Pechmann: First, the strength and location of this earthquake was not really a surprise to any seismologist or earthquake geologist who's familiar with Utah's earthquake history. There was a magnitude 4.9 earthquake out near Magna in 1962, which caused some damage.

And from 1962 to 2020, there were some smaller earthquakes near Magna and in a belt extending across the northern end of the Salt Lake Valley. This was basically a magnitude 5.7, which seismologists consider to be moderate size. We can get much bigger earthquakes here in Utah, magnitude 7 to 7.7. The shaking from a magnitude 7 earthquake would be about 20 times stronger than the shaking from the Magna earthquake and it would last longer as well. So, the strong shaking for a magnitude 7 would probably be around 30 seconds. For the Magna earthquake, the strongest shaking downtown only lasted three to five seconds, but even three to seconds can seem like a very long time. You could feel the ground moving, though, for quite a bit longer than that, at least 20 seconds probably downtown during the Magna shaking.

So, what did we learn? We actually learned quite a lot. This earthquake occurred six and a half miles beneath the northwestern part of Salt Lake Valley on a fault that slants downward to the West at a relatively shallow angle, like 34 to 39 degrees from the horizontal. This shallow angle between the fault surface and the horizontal, which is called the dip, was the most significant and surprising observation from the Magna earthquake. Here's why.

First, it's more likely than not that the Magna earthquake occurred on the Wasatch fault. We can't say for sure that it did because we don't know how deep the Wasatch fault is out beneath the western part of the valley. But whether or not the Magna earthquake occurred on the Wasatch fault, the fact that it occurred on such a shallowly dipping fault tells us that the dip of the Wasatch fault has to be the same or shallower, something like 30 to 40 degrees, at least in the northern Salt Lake Valley.

This conclusion is based on physical and numerical models of how smaller, secondary faults form in the rock above major faults like the Wasatch fault. Basically, the dips of these secondary faults are steeper than or equal to the dip of the underlying main fault.

So, the 30 to 40 degree dip for the Wasatch fault from the Magna earthquake is shallower than what was previously assumed based mostly on observations from earthquakes elsewhere. The implication here is that the Wasatch fault is closer to the ground surface than was previously thought, at least in the northwestern Salt Lake Valley. Therefore, the ground shaking in this part of the valley will be stronger than we thought during a future large, around magnitude 7, earthquake on the Salt Lake City section of the Wasatch fault. And we expect that such an earthquake will occur at some point in the future.

Julie Kiefer: And is this the type of information that is factored into making these maps, how shallow or how deep the faults are and that leads to either increasing or maybe less shaking on the ground?

Jim Pechmann: Yes, that is part of the information that goes into these maps, is the dip on the fault surface. Faults are not all vertical. Some of them basically are at an angle with the ground surface. So, the Salt Lake City segment of the Wasatch fault actually extends underneath the whole Salt Lake Valley. It's not just over on the east side of the Salt Lake Valley.

So, I was a participant in a meeting with Kris Pankow from the Seismograph Stations and several other people with USGS folks in which we talked about how to basically characterize the dip of the Salt Lake City segment in light of the new information from the Magna earthquake. And I think that got into the final maps, but I haven't dug deep enough yet to see for sure.

Julie Kiefer: And is that area, now that we know that there's been a relatively big earthquake there in Magna, does that mean it's prone to future larger earthquakes like that?

Jim Pechmann: Probably, yes.

Julie Kiefer: Coming back to the map, what does it show for the country and earthquake hazards across the U.S.?

Jim Pechmann: Zooming up from Magna, the USGS map that we were talking about earlier shows that nearly 75 percent of the United States has at least a 5 percent chance of damaging ground shaking from earthquakes during the next 100 years. In some places, this probability is far higher, it's greater than 95 percent. There's 25 states that have places with at least a 25 percent chance of damaging ground shaking within 100 years. So, for the purposes of this map, damaging ground shaking is defined as anything that causes slight or greater damage comparable to what occurred in downtown Salt Lake City during the Magna earthquake.

Julie Kiefer: Is that a change from what we thought before? I mean, that's a big part of the country that has an earthquake hazard associated with it.

Jim Pechmann: The calculated seismic hazard increased in some places and it decreased in other places. Overall, it looks like the area of increased hazard is larger than the area of decreased hazard. Some of the places where the hazard increased the most by one measurement or another are southern Alaska, the Big Island of Hawaii, coastal California, central Wyoming, south central Utah, the Memphis area and the central and northeastern Atlantic coastal corridor.

Let me say a little bit more about Utah here. So, the seismic hazard in the Wasatch Front region did not change very much. The new maps do show higher hazard in south central Utah than the previous 2018 maps did. I'm surprised that the hazard didn't change more in the Wasatch Front region because there were some significant changes in the methodology that was used to make these maps. In Salt Lake City, the estimated hazard decreased by 1 to 4 percent depending on the measurement of ground shaking that is used, but this decrease is not really meaningful at all given the uncertainties in these maps. It's down in the noise level 1 to 4 percent.

Julie Kiefer: So, what accounts for some of these changes? You had said there's been some changes in the methods for getting this information in the first place?

Jim Pechmann: Yes, there's lots of  them. Well, one of the things that was done is they included a lot of faults that were not in the maps before because they didn't have information on how fast these faults moved, what's called the slip rate, which is usually expressed in something like millimeters per year or centimeters per year averaged over centuries or millennia.

And what they did is they decided that based on the age category, they would assign some generic slip rate to them. Also, there were, I think, four different groups that used GPS data measurements of basically slow movement of the surface of the Earth to try to estimate rates of movement on faults. And those were incorporated into the maps. They were in the previous version of the maps, maybe the previous two versions, but not with very much weight. They had a much higher weight this time.

There were differences in the way that they used seismicity data. In, I think in Utah, one of the things that affected the maps was that they moved the boundary that was the divide between equations that are used to predict ground motions in the Western U.S. and in the Eastern U.S. In Eastern U.S, basically you can feel an earthquake of a given size much farther away because the seismic waves decrease in amplitude with distance a lot more slowly.

Julie Kiefer: Okay, interesting. So, a lot of just more accurate measurements of how the Earth moves and where that's happening, I guess.

Jim Pechmann: Right. And another thing that they did was to basically allow more flexibility in how many different sections of a fault could break at once in an earthquake. So, this was accounted for in the previous maps, but not really in the same way.

Julie Kiefer: And so, you now, if we look at the whole country, what are the states that have the highest likelihood of experiencing a damaging earthquake in the next 100 years?

Jim Pechmann: So, there are three states which have areas where the chance of damaging ground shaking in the next 100 years is greater than 95 percent. Those states are Alaska, Hawaii and California. That's no surprise.

Julie Kiefer: Yeah, no surprise!

Jim Pechmann: So, there's several additional states which have areas where the chance of damaging ground shaking is in the next highest category, 75 to 95 percent. These areas are the Puget Sound region of Washington, Western Nevada, the area around the New Madrid Seismic Zone in southeastern Missouri and the area around Yellowstone National Park. So, in the Yellowstone region, a large earthquake is much more likely than a large explosive volcanic eruption like the ones featured in Yellowstone disaster movies.

Julie Kiefer: But the earthquake would come from volcanic activity underground? Is that the source of it?

Jim Pechmann: It's related to it. There was a magnitude 7.3 in 1959 in Hebgen Lake, which is near Yellowstone. It was not directly related to volcanic activity as far as I know. And that was a pretty big-sized earthquake.

Julie Kiefer: Okay. And there's also this interesting red spot at the corner of Arkansas, Tennessee and Kentucky. What causes that instability there?

Jim Pechmann: That's the New Madrid Seismic Zone. And there were some large earthquakes. There were a series of them in 1811, 1812, that were felt for very large distances. There've been some smaller earthquakes since then, but nothing close to a 7. And basically nobody really knows why earthquakes occur there. It's a very interesting question and one that some seismologists spend a lot of time worrying about, especially with regards to safety of critical facilities like nuclear power plants and dams. If we don't really understand why earthquakes occur in Missouri or in Ohio or in South Carolina, other kind of hot spots, then can we rule them out elsewhere in the Eastern U.S.?

Julie Kiefer: Right. Yeah, that's a really interesting question. And what that also points to is that we really can't predict when earthquakes are going to happen, at least not in the same way that we can like a hurricane or a tornado. I mean, you talked about this a little bit, but why is it hard to predict earthquakes?

Jim Pechmann: Well, let's talk about what we mean by prediction here. So, when sufficient data are available, earthquake scientists can make pretty good predictions about where large earthquakes will occur, how often they will occur, how big they will be and how much ground shaking they will generate in different places.

So the National Seismic Hazard maps kind of put all of this information together and show it in these various maps. So, what we cannot do is predict exactly when large earthquakes will occur, not even to within a few months or years.

Why are they hard to predict? They're hard to predict because no one has yet found any signals that reliably indicate that a large earthquake is imminent. It's difficult to look for such signals because the time intervals between large earthquakes on any given section of fault is at least a few decades, even on very active faults.

Another problem with predicting earthquakes is that we don't have much good real-time information about conditions miles deep in the Earth where large earthquakes tend to initiate. So, you mentioned hurricanes, tornadoes and snowstorms. We know a lot more about conditions in the atmosphere where hurricanes, tornadoes and snowstorms develop. That's because we can observe the atmosphere with instruments and weather stations, satellites, airplanes and weather balloons. So atmospheric scientists use these observations as input to sophisticated computer models that project the state of the atmosphere into the future using well-known physics. The output from these computer models provides a means to predict hurricanes, tornadoes and snowstorms.

When it comes to earthquakes, we just don't have the observations or the computer models deep in the Earth where it counts.

Julie Kiefer: Yeah, and that's a whole different timescale. Yeah, it's an interesting problem. I mean, these maps have so much information in them. It sounds like they are created on a regular basis. How often does that happen?

Jim Pechmann: Every few years. So, the first USGS National Seismic Hazard Map was published in 1976. Since then, the USGS has published updated and improved versions every few years, it varies a little bit. They've also expanded this one map into a series of related maps starting in the 1980s. The recent versions of these maps are far better than the earlier ones and are put together by much larger teams. The current versions of the National Seismic Hazard Maps were completed in 2023 and were officially released to the public on January 16th of this year.

The 2023 maps are the first to cover all 50 states at the same time. The previous versions of these maps were completed in 1998 for Hawaii, in 2007 for Alaska and in 2018 for the other 48 states, which are known as the conterminous United States.

Julie Kiefer: What goes into making maps like these?

Jim Pechmann: Well, they are a lot of work.

Julie Kiefer: Yeah, I bet!

Jim Pechmann: Each update to these maps is now a multi-year effort carried out by a very large team with opportunities for input from outsiders via online workshops. So, the work for the 2023 update began in 2020, but the USGS team members are pretty much always working on these maps or on related research.

So to give you an idea of the size of the team, the main technical paper about the 2023 maps has 54 authors, 46 of whom have a USGS affiliation. But the number of people who contributed to the 2023 maps is actually far larger than the number of co-authors on the paper.

The National Seismic Hazard Maps use lots of data and research results that come from earthquake scientists working in universities, state geological surveys and consulting firms. Some of the input used in these maps has come from the University of Utah, other universities in the state and the Utah Geological Survey.

The input data that I'm talking about includes maps of active faults and information from geologic studies about the average slip rates on these faults and how often earthquakes occur on them.

Another important piece of data for these maps is an earthquake catalog for the United States. By an earthquake catalog, I mean a list of the times, locations and magnitudes of earthquakes that have occurred in the country, large and small.

The earthquake catalog for Utah and for Yellowstone National Park comes primarily from the University of Utah Seismograph Stations.

Julie Kiefer: These maps are actually really useful. They're used for a lot of things. What are some of those things?

Jim Pechmann: Probably the most important application of the maps is in building codes. So, the maps are used to provide the earthquake ground motions that buildings must be designed to withstand without collapsing. And these design ground motions vary quite a bit depending on location. So that's one use.

Insurance companies use the maps to set earthquake insurance premiums. The Federal Emergency Management Agency uses the maps as one of the criteria for determining how to allocate federal resources for earthquake preparedness and mitigation.

And, finally, the National Seismic Hazard Maps provide a uniform standard of reference for in-depth seismic hazard analyses that are typically carried out for critical facilities such as dams and nuclear power plants. So if you're doing such a study, you're always going to look at the national map and see how your numbers compare to them.

Julie Kiefer: But as we saw, it's a changing landscape. I mean, every couple of years there's new data and new assessments. I'm sure it's hard for a lot of these organizations to keep up with that.

Jim Pechmann: And another thing to keep in mind is that the national maps are, they're taking a fairly broad brush approach because they're doing the whole country. If you want to build a critical facility and get it licensed by, say, the Nuclear Regulatory Commission, you're going to be expected to go beyond what the USGS does for that particular site.

Julie Kiefer: So, predicting earthquakes is challenging, but we can all take steps to be prepared. Jim, what do you do to prepare for earthquakes?

Jim Pechmann: First of all, I live in a wood-frame house. I don't live in an unreinforced brick house, of which there are many . . .

Julie Kiefer: My house!

Jim Pechmann: . . . especially in the area around the University of Utah. Let's see, all the furniture in my office is bolted to the wall. That's true for everybody in the Seismograph Stations. I keep bedroom slippers by my bed, so if there's an earthquake and glass shatters, I can get up and walk away without having to walk through broken glass.

What else do I do? I don't have any heavy things on any shelves above my bed or anywhere else that can fall on me or anybody on my family during an earthquake. We store food and water. We've got actually more than enough for surviving for 72 hours without any supplies.

Julie Kiefer: Where is the best place to go in a house if there's an earthquake happening?

Jim Pechmann: So, the most dangerous place to be in an earthquake is going into or out of a building. That's where you're most likely to get hit by something. So if you're inside, you should stay inside and get under a strong table or desk and hold onto it so it doesn't slide out from on top of you. So, duck, cover and hold, that's what you need to remember. And if you're outside, you should stay outside and get away from buildings, power lines and anything else that might fall on you.

Julie Kiefer: And where can people go to find more information about how to be prepared?

Jim Pechmann: A very good source of information on earthquake preparedness is a booklet called “Putting Down Roots in Earthquake Country: Your Handbook for Earthquakes in Utah.” There's a new edition that was published in 2022 and it's available online at

Julie Kiefer: And if you were to give advice to people who are listening, what's the one piece of advice you would give? I mean, how should we be thinking about earthquakes? What do you think people don't understand about earthquakes? Or what do you think people should know?

Jim Pechmann: Well, Utah is earthquake country, as you said, and a large damaging earthquake could happen at any time. You can't just stress out about it all the time, but you should do what you can to be prepared. And one of the most important things is to pay attention to the types of buildings where you and your family spend a lot of time, such as your homes, schools and workplaces.

As I mentioned, Utah has a lot of old unreinforced, brick and masonry buildings that are very susceptible to damage and collapse in earthquakes. They were outlawed in California back in the 1930s. They were legal to build here in Utah up through the mid-1970s. So, the Magna earthquake demonstrated the vulnerability of these buildings quite well. Basically, you should try to avoid spending many hours a day in such buildings unless they've been seismically reinforced. So, wood-frame structures, on the other hand, tend to hold up very well in earthquakes because they can bend and sway like a tree in the wind, but they have to be bolted to the foundation. Some of the really old wood-frame houses are not necessarily bolted to the foundation. So that's one thing.

And then there's the things I mentioned. You want to move or secure any heavy objects or furniture that could fall on you when the ground shakes, especially where you sleep. You should know how to shut off the gas supply to your house. Keep a wrench handy for this purpose, but you should not shut off the gas after an earthquake unless you smell a gas leak. So only shut it off if you smell gas. There's a lot of other information in the Roots booklet that's worth looking at.

Julie Kiefer: Well, we'll be sure to take a look. This is good advice, Jim. Thank you very much for being my guest on U Rising.

Jim Pechmann: You're certainly welcome.

Julie Kiefer: Listeners, that's it for today's episode. Our executive producer is Brooke Adams and our technical producer is Robert Nelson. I'm Julie Kiefer. Thanks for listening.