UGS Hosts Basin and Range Province Earthquake Working Group Meeting

In March 2006, the Utah Geological Survey (UGS) organized and hosted a three-day meeting of the Basin and Range Province Earthquake Working Group (BRPEWG) in Salt Lake City. The BRPEWG was convened under the auspices of the U.S. Geological Survey (USGS) National Seismic Hazard Mapping Project (NSHMP) and the Western States Seismic Policy Council to provide consensus recommendations to the USGS on five seismic-hazard issues in the Basin and Range Province (BRP) important to the 2007 update of the USGS National Seismic Hazard Maps. These maps form the basis for the seismic design requirements in the International Building Code, and as such are important in ensuring the safety of new buildings in Utah. The BRPEWG consisted of 27 geologists, seismologists, and geophysicists who are leading experts on BRP earthquake hazards. The five seismic-hazard issues considered by the BRPEWG were first identified by scientists who attended the Basin and Range Province Seismic Hazard Summit II (BRPSHSII) held in Reno, Nevada, in 2004. The five issues were:

1. use and relative weighting of time-dependent, Poisson, and clustering models in characterizing fault behavior,
2. proper magnitude-frequency distributions (Gutenberg-Richter versus characteristic earthquake models) for BRP faults,
3. use of length versus displacement relations to estimate earthquake magnitude,
4. probabilities and magnitudes of multisegment ruptures, and
5. resolving discrepancies between geodetic extension rates and geologic slip rates.

The BRPEWG consensus recommendations were published in UGS Open-File Report 477, Basin and Range Province Earthquake Working Group Seismic-Hazard Recommendations to the U.S. Geological Survey National Seismic Hazard Mapping Program, and were presented for USGS consideration at the NSHMP Intermountain West regional meeting held in Reno, Nevada, in May 2006. For those interested in the details of the BRPEWG process and recommendations, Open-File Report 477 is available from the Utah Department of Natural Resources Map & Bookstore, as is the BRPSHSII Proceedings Volume published by the UGS as Miscellaneous Publication 05-2.