Probabilities of a magnitude 6.75 or greater earthquake on the region's faults in the next 50 years; the whole Wasatch fault is 18 percent. Only faults at 2 percent or more are shown. USGS, after the Working Group on Utah Earthquake Probabilities (2016).
The Working Group on Utah Earthquake Probabilities (WGUEP) has made the first comprehensive forecast of its kind in the Intermountain West. In the next 50 years, the Wasatch Front region has a:
- 43 percent chance of one or more earthquakes of magnitude 6.75 or greater;
- 57 percent chance of one or more of magnitude 6.0 or greater.
Like a forecaster's chance of rain, the numbers give the likelihood of an earthquake of a given size somewhere in the region — useful for seismic hazard analysis and for public policy on reducing earthquake losses.
Why the Wasatch Front
The region's dramatic relief is the product of faulting. Large earthquakes here happen on faults along the base of ranges such as the Wasatch Range.
- The Wasatch fault zone is the region's longest, most active and most hazardous fault. Its movement created the Salt Lake and Utah Valleys — home to the Wasatch Front urban corridor, which the fault borders and in places crosses.
- At stake: the corridor holds nearly 80 percent of Utah's 3 million people and more than 75 percent of its economy.
The probabilities
| Source | M6.0 or greater | M6.75 or greater |
|---|---|---|
| Wasatch fault zone | 18% | 18% |
| Oquirrh–Great Salt Lake fault zone | 7% | 6% |
| Other faults in the region (45 faults or sections, combined) | 34% | 25% |
| Background earthquakes (not on known faults) | 14% | not calculated |
| Wasatch Front region total | 57% | 43% |
- Prehistoric quakes: the forecast draws on new geologic evidence of the timing and location of large prehistoric earthquakes. At least 22 have ruptured parts of the Wasatch fault between Brigham City and Nephi in the last 6,000 years.
- Historical quakes: a reevaluation of earthquakes since settlement gauges the chance of moderate M5.0 to 6.75 "background" earthquakes away from known faults.
Historical earthquakes in Utah and surrounding states, 1850 to June 2015. Inset: a trench across the Wasatch fault near Santaquin exposes layers broken by a large prehistoric earthquake. USGS, after the Working Group on Utah Earthquake Probabilities (2016).
What a large earthquake could do
A large quake on the Wasatch fault near Salt Lake City could cause:
- 2,000 to 2,500 deaths;
- 7,400 to 9,300 life-threatening injuries;
- 84,000 families displaced;
- water, power, gas and sewer outages lasting days to months;
- more than $33 billion in short-term economic losses.
Faults in undeveloped areas matter too: a large earthquake on one of them could still damage and disrupt the urban corridor.
Being ready
Large earthquakes can come at any time. The numbers may be refined as new data come in, but the threat is clear: individuals can prepare and reduce their risk, and communities can push for earthquake-resilient design and disaster planning.
Sources
Based on Earthquake Forecast for the Wasatch Front Region of the Intermountain West, USGS Fact Sheet 2016–3019, U.S. Geological Survey (DOI), summarizing the Working Group on Utah Earthquake Probabilities (2016) — scientists of the Utah Geological Survey, the USGS, URS Corporation and the University of Utah — with support from the USGS National Earthquake Hazards Reduction Program, and citing Pankow and others (2015) and the Utah Seismic Safety Commission (2008); a work of the United States government in the public domain. The maps come from the fact sheet's PDF. More: Utah Geological Survey hazards and USGS Earthquake Hazards.
Licence: CC0 1.0 (public domain) · Adapted from pubs.usgs.gov
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