RAPID DEFORMATION RATES ALONG THE WASATCH FAULT ZONE, UTAH, FROM FIRST GPS MEASUREMENTS WITH IMPLICATIONS FOR EARTHQUAKE HAZARD

Anomalously high rates of crustal deformation have been measured al th e Basin-Range transition to the Rocky Mountains along the Wasatch faul t zone, Utah, by repeated Global Positioning System (GPS) measurements . Four GPS field campaigns (1992-1995) and comparisons with older (196 2-1991) geodetic data have revealed east-west extensional strain at a rate of 0.05 +/- 0.02 mu strain/yr, corresponding to a 2.7 +/- 1.3 mm/ yr rate of horizontal displacement across a 55-km wide area. This rate is more than 20% of the total similar to 12 mm/yr extension rate acro ss of the similar to 800-km wide Basin and Range province. It is also two to three times larger than the average Late Quaternary fault slip rate on the Wasatch fault and tens of times larger than the displaceme nt rates inferred from the cumulative seismic moments of historic eart hquakes. While we do not yet know the source of this unexpected contem porary deformation, possible mechanisms include homogeneous crustal ex tension, loading of the Wasatch and adjacent faults, and pressure solu tion creep. If the Wasatch fault is being loaded by this high strain r ate, it increases the expected peak ground acceleration significantly from standard values. These new findings demonstrate the importance of GPS in earthquake hazard assessment.