Earthquake studies are nothing new to Utahns, but a recent study conducted by the University of Utah gives a new perspective on potential earthquake damage assessments.
Philip C. Emmi, associate professor of geography, and Carl A. Horton, network coordinator for the Digitally Integrated Geographic Information Technologies (DIGIT) laboratory, have released a series of computer-generated maps showing the amount and spatial distribution of risk to property and persons in Salt Lake County due to ground shaking in an earthquake. The two researchers from the University of Utah have been conducting their research for the past four years.Unlike some recent predictions about when and where an earthquake will occur, Emmi and Horton have focused their study on the potential risk to property and life. There have been studies done on the likelihood of an earthquake occurring on or near the Wasatch front, and that research underlies the study done by Horton and Emmi.
The pair from the U. have generated maps that divide the damage into three categories: loss to residential structures, loss to commercial structures and loss to lives (occurring in both the residential and commercial structures).
Geological data about Salt Lake County has enabled the scientists to predict which areas would be affected and at what magnitude.
The greater the intensity of ground shaking, the greater the loss to home and buildings and, thus, the greater the risk to life and limb. Unreinforced masonry buildings have the poorest performance during an earthquake, while wood and light metal frames perform the best.
The study estimated losses using data on expected ground-shaking intensities, structural frame type, and structural repair and replacement costs. The levels of loss have a 10 percent chance of being reached or exceeded over short (10-year), intermediate (50-year), and long (250-year) exposure periods. This also means there is a 90 percent chance that these figures will not be reached in the given exposure period.
The likelihood of an earthquake and of more severe or multiple quakes increases with the longer exposure periods.
Estimated losses for residential structures over the 10-year exposure period are $441 million or 7.2 percent of replacement value. Loss to each structure would vary depending on the location and structural frame type.
"These injuries and losses are expected to be concentrated in the area bounded on the north by South Temple, the east by Foothill Boulevard, on the south by I-80, and on the west by West Temple," said Emmi.
Comparable figures for the intermediate (50-year) period are $1.15 billion or 19 percent of the value of the residential structures.
Damage to commercial structures in a 10-year exposure period are estimated at $327 million (13 percent of value). The greatest concentrations are in the central business districts and southward between I-15 and 400 East, and south to Murray.
Over a 50-year exposure period, damages to commercial structures would be $783 million (30 percent of value).
The data used in figuring the monetary losses were taken from the Salt Lake County assessor's office, so buildings owned by the state, a church, or any other non-taxable organization would not be included. The number of injuries and loss of lives do include employees that work in these buildings because the numbers were taken from the employment statistics and the researchers did include those who work for non-taxable companies.
Further research should include a balanced focus on refining an understanding of local geology and on learning more about the seismic performance of local buildings, how to encourage owners to improve their structures and how to do so in the most efficient manner, says Emmi.
Salt Lake County
Possible Earthquake related injuries within
Injury 10 years* 50 years* 250 years*
Minor injury 644 7,300 18,901
Major injury 70 1,245 4,476
Loss of life 21 351 1,093
*There is a 10 percent chance this many people would be injured or killed by earthquakes within the time span listed.