Utah Earthquake Country Examined

By David Demille | May 2, 2016

Signs of earthquakes are everywhere in the chaotically beautiful geology of southwest Utah and the region where the mile-high Colorado Plateau falls off into the corrugated Basin-and-Range landscape that dominates neighboring Nevada.

The treeless desert lays bare the lines of rock, and along the tell-tale straight lines of some of the area’s more prominent faults, geologists are busy studying the ways they’ve shaped the area’s past – and how they might impact the future, the Spectrum reported.

“With the growth and increase in population, we’re really trying to look more closely and study the area,” said Tyler Knudsen, a geologist with the Utah Geological Survey and part of the team that published an update earlier this year on the Washington Fault, which runs from the Arizona Strip northward through Washington Fields and the middle of Washington City.

The fault was near the epicenter of the area’s largest earthquake of the recent past, a 5.8 magnitude event 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 major danger to some of the area’s older buildings, and with the population nearly three times as large and with many more homes built atop cliff sides or beneath rock fall areas, the potential for damage is probably greater, Knudsen said.

earthquake-coverageThere 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 in some spots thousands of feet and creating the rainbow-colored scenery of Cedar Breaks and the Kolob District of Zion.

The best guess today is that a magnitude 7 earthquake or larger could hit the Hurricane Fault, Knudsen said, while a 6.5 or greater is possible along the Washington Fault. 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.

“There’s the potential for a lot of seismic energy to carry a long way,” he said.

Predicting when an earthquake might happen and how powerful it might be is difficult though.

In recent weeks, a number of earthquakes have been measured throughout the area.

Last week a 3.7 magnitude earthquake was felt in the Mesquite area, with the epicenter in the nearby Arizona Strip. Several more have been measured in and around the area in the past few weeks.

A 4.3 magnitude event shook the community of Enterprise and its neighbors on Jan. 15, less than a week after a 3.3 magnitude earthquake was measured in the same area.

What all that means is hard to say in terms of future predictions, Knudsen said, although they are reminders that this is earthquake country.

Utah’s potential as a site of future earthquake damage gathered attention with the release of a troubling report about 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.

A military response operation called “Operation Seismos” was conducted in Cedar City in January, with the Utah National Guard, Iron County Emergency Management and local law enforcement entities teaming up to test their capabilities based on the scenario of a 7.7 magnitude earthquake.

Nearly 60,000 people across southwest Utah participated in the annual Great Utah ShakeOut, an annual preparedness exercise sponsored by emergency services organizations across the state.

Utah businesses, schools, government groups and others took part in the exercise, including emergency response coordinators from Washington County that used the opportunity to test their own plans based on earthquake scenarios.

Pete Kuhlmann, emergency services director for the county, said the exercise is always a good reminder of the unique potential for region-wide destruction in a major earthquake. The area isn’t prone to most other types of natural disasters, and flooding, while common, is typically limited to particular areas, while damage from an earthquake could be much more widespread.

“We still have some who just think someone’s going to ride in on a white horse and save them,” Kuhlmann said. “In a catastrophic event, there aren’t enough people or white horses.”

Utah residents have several resources available to help with earthquake preparedness, including the Great Utah Shakeout website.

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 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 online at www.utah.gov.

About David Demille

The Spectrum

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