GEOLOGIC HAZARDS

The UGS and U.S. Geological Survey (USGS) established the Working Group on Utah Earthquake Probabilities (WGUEP) in 2010 to develop forecasts of large earthquakes along the Wasatch Front. The forecasts were developed with the intention that they would help heighten the public’s awareness and understanding of the region’s seismic hazards, similar to what the forecasts of the Working Group on California Earthquake Probabilities (WGCEP) have successfully done.

The WGUEP employed a methodology similar to that used in the Uniform California Earthquake Rupture Forecast process, implementing a fault model, deformation model, earthquake rate model, and probability model. The WGUEP developed 30-, 50-, and 100-year forecasts that include (1) combined time-dependent and time-independent probabilities of large earthquakes (moment magnitude [M] ≥ 6.75) for the five central segments of the Wasatch fault zone and two segments of the Great Salt Lake fault zone, (2) time-independent probabilities of large earthquakes on 45 less well-studied faults and fault segments, and (3) estimates of the time-independent probabilities of background earthquakes in the M 5.0–6.75 range. Results include 50-year probabilities of 43% for one or more M ≥ 6.75 earthquakes and 57% for one or more M ≥ 6.0 earthquakes occurring within the Wasatch Front region, and 18% for one or more M ≥ 6.75 earthquakes occurring on the Wasatch fault zone.

The final WGUEP report (UGS Miscellaneous Publication 16-3) consists of a 164-page main report as well as five appendices that include a summary of moment magnitude regressions considered by the WGUEP, a comprehensive analysis of paleoseismic data for the central segments of the Wasatch fault zone, and a newly compiled and processed historical and instrumental earthquake catalog for the Wasatch Front and surrounding Utah region.

Partial funding for the WGUEP was provided by the National Earthquake Hazards Reduction Program.