Signs of earthquakes are everywhere in the geology of southwestern Utah.
Placed right where the mile-high Colorado Plateau falls off into the corrugated Basin-and-Range landscape that dominates neighboring Nevada, the desert lays bare the lines of rock and tell-tale straight lines of large faults.
Geologists are busy studying the ways they’ve shaped the area’s past — and how they might impact the future.
The fault was near the epicenter of the area’s largest earthquake of the recent past, a 5.8 magnitude event recorded in 1992 that shook residents across the county and did damage as far away as Springdale, where a landslide destroyed several homes and forced the closure of the highway leading into Zion National Park.
Such an earthquake today could pose a major danger to some of the area’s older buildings, and with today’s population nearly three times as large and with many more homes built atop cliffsides or beneath rockfall areas, the potential for damage is greater.
There is speculation the Washington Fault might actually merge at some point with the much larger and more studied Hurricane Fault, which follows a parallel line to the east.
There, the Hurricane Cliffs are the visible product, rising thousands of feet in places and creating the rainbow-colored scenery of Cedar Breaks and the Kolob District of Zion.
The best guess today is a magnitude 7 earthquake or larger could hit the Hurricane Fault, said Tyler Knudsen, a geologist with the Utah Geological Survey who has studied and published multiple papers on faults in southern Utah.
A 6.5 or greater is possible along the Washington Fault and, if they’re connected, it’s possible that a slippage along one fault line could cause ripples along the other, spreading the potential for damage across most of the populated area in Washington County and its immediate neighbors.
A smaller earthquake in line with the power of the 1992 event is more likely to happen in any given year, but that could still do significant damage, especially to some of the older masonry buildings in the area, Knudsen said.
Predicting when an earthquake might happen, and how powerful it might be is difficult though. In a place as seismically active as the U.S. Southwest, earthquakes are a regular occurrence.
On Monday, seismologists measured a 4.4 magnitude quake in the Littlefield area on the Arizona Strip between St. George and Mesquite, followed by a 1.6 magnitude aftershock less than an hour later.
There had been 23 measurable earthquakes within the last three weeks in southwestern Utah, northwestern Arizona and southeastern Nevada, according to USGS reports.
What all that means is hard to say in terms of future predictions, Knudsen said, although they are reminders that this is earthquake country.
Additional research in the past five years suggests that much of Utah could experience a large earthquake at any time. One report published in 2018 studied a major fault along the Wasatch Front, with scientists concluding that the probability of a 6.75-or-greater magnitude earthquake hitting the heavily populated area was about 43 percent over the next 50 years.
“Considering that the average age of Utah’s citizens is the youngest in the nation at about 29 years, there is a realistic chance that many current residents will experience a large earthquake in their lifetime,” said Ivan Wong, principal seismologist at Lettis Consultants International and lead author of the report.
Farther to the south, studies haven’t gone as far as to predict the likelihood of an earthquake, and some evidence indicates the problem isn’t as serious — about 60 percent of all 3.0-and-larger earthquakes statewide happen along the Wasatch Fault — but local officials are trying to learn what they can from some of the news from up north.
The latest edition of the “Putting Down Roots in Earthquake Country” handbook updated this year by the USGS, describes several different earthquake scenarios that could hit the state’s lower half.
Not that authorities across the state aren’t working to be ready.
Every April, law enforcement agencies, local governments and emergency response teams participate in the Great Utah ShakeOut, an annual preparedness exercise sponsored by emergency services organizations across the state.
Utah businesses, schools, government groups and others take part in the exercise, including emergency response coordinators from Washington County who use the opportunity to test their own plans based on earthquake scenarios.
Utah residents have several resources available to help with earthquake preparedness, including the Great Utah Shakeout website, shakeout.org/utah.
Be Ready Utah, the state’s emergency preparedness program run by the Division of Emergency Management, shares information about earthquakes and other hazards on its website, BeReadyUtah.gov, and on social media.
The Utah Seismic Safety Commission publication Putting Down Roots in Earthquake Country—Your Handbook for Earthquakes in Utah gives information on earthquake hazards and preparedness, and is available at beready.utah.gov/utah-hazards/earthquakes.
David DeMille writes about southwestern Utah for The Spectrum & Daily News, a USA TODAY Network newsroom based in St. George. Follow him at @SpectrumDeMille or contact him at firstname.lastname@example.org. To support and sustain this work, please subscribe today.