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Utah Geological Survey
Two trenches excavated across the Wasatch fault near the University of Utah reveal new information on large earthquakes that have occurred in the Salt Lake City area.

SALT LAKE CITY — Two trenches excavated across the Wasatch Fault near the University of Utah reveal new information on large earthquakes — those of at least magnitude 7 or higher — that have occurred in the Salt Lake City area.

Geologists have found evidence of at least five large earthquakes occurring in the past 14,000 years.

Their findings were showcased Wednesday by geologists from the Utah Geological Survey and the U.S. Geological Survey, who explained the lessons being extracted from the gaping holes in the ground.

The site, located on the east-bench segment of the fault, provides one of the last opportunities to study the fault in the Salt Lake area. Elsewhere, extensive development has mostly obscured parts of the Wasatch Fault that extend through the city.

"This is the first time we've been able to do this, because the area is so extensively developed," said the Utah survey's Chris DuRoss.

After obtaining permission from property owners, a team of geologists descended on the hilly site of a former orchard and got to work three weeks ago.

They are hopeful the fault scarps — the disruptions of surface soil — can enhance their understanding of how often large earthquakes occur in the Salt Lake area and their magnitude.

Gathering that information will help scientists evaluate the likelihood of the next large earthquake in the area and calculate the severity of earthquake ground shaking that should be expected in the future. In addition, the data will help improve seismic-hazard analyses of the region and how the West Valley and Wasatch Fault zones interact. The West Valley fault zone will be studied this fall by the Utah Geological Survey.

Senior geologist Mike Hylland is hopeful the September field study of the West Valley fault will help scientists better understand the seismic hazards of the area.

By comparing activity at the two faults, the survey hopes to learn if the faults act independently of one another or are interrelated.

"We want to see how they fit together, or not," Hylland said. "There could be activity that happened at roughly the same time, or at completely different times, or a mix of the two."

The project is partially funded by a grant from the national survey's Earthquake Hazards Reduction Program.

e-mail: amyjoi@desnews.com