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Utah Geological Survey studies faults on west side of Salt Lake Valley

Posted at 8:17 PM, May 15, 2023

MAGNA, Utah — It has been three years since a 5.7-magnitude earthquake rocked much of northern Utah.

Then last summer, the Utah Geological Survey dug a long trench to study two faults on the west side of the Salt Lake Valley.

Geologists study thousands, even millions of years of evidence, but the geologists with the UGS have been rushing to get the evidence available in the few places yet to be developed above these faults.

In the summer of 2022, geologists Adam Hiscock and Emily Kleber helped lead the team digging the trench near Indiana Avenue on Salt Lake City's west side — one of very few undeveloped pieces of land over a fault in the Salt Lake Valley.

"Because we have to have a scar, which is the surface expression of the fault that hasn't been modified," Hiscock said.

It's almost a race against time for them.

"In fact, the airport east trench that we did the fieldwork for ... in 2015, that site is gone now," Hiscock said.

Utah's major mountain valleys are striped with faults.

"These are indicating where geologists see evidence of past earthquakes that have ruptured the surface," Kleber said, showing a map of the Salt Lake Valley with color-coded lines.

The Indiana Avenue trench allowed them to see fault activity for the last 15,000 years, give or take. Layers of soil reveal how the ground has moved.

Other diagrams, which the pair of UGS geologists showed FOX 13 News, demonstrate how land went down or went up based on the striations of the different zones.

"And these are kind of mapped out on here like this. This is the Gilbert Deposit," Hiscock explained in the video above. "As it's coming along this side of the figure is east to west, it's faulted down. And on the scale on this... the offset on there is probably five, six centimeters.

Their work complements the extensive study of the 5.7-magnitude 2020 Magna earthquake, illustrating the three-dimensional reality of faults — which are far more than a line on the surface.

The research shows that underneath the ground, a fault can meet another fault several miles away.

"The Magna earthquake was really valuable to us and seismologists at the University of Utah," Hiscock said. "It was really well-studied with sensors in the valley, [which] then picked up all the data from all these earthquakes, and from that data we can better model what these faults look like under the valley."

Those connected faults mean when one fault moves, others may follow.

"More often than not, what we found is that the Wasatch fault zone can trigger earthquakes on the West Valley fault zone," Kleber said.

The UGS geologists are deepening their knowledge of our local faults, but their work helps us all understand where we live. What we see above the surface in the shape of our valleys — mountains sloping west from the east and sloping east from the west — underground faults are doing the same thing and meeting each other far below the surface.