Contemporary deformation of the Wasatch Fault, Utah, from GPS measurements with implications for interseismic fault behavior and earthquake hazard: Observations and kinematic analysis

Contemporary strain accumulation rates of the 350-km-long Wasatch fault, Utah, have been determined by GPS measurements and provide key data for evaluating normal fault behavior and related earthquake hazard assessment. This paper presents a complete description of the Wasatch GPS network, data archiving and processing, and the measured ground deformation. The network spans the Wasatch fault in an area ∼300-km long and ∼200-km wide in north and central Utah and consists of 43 GPS sites surveyed in 1992, 1993, 1994,1995, 1999, 2001, and 2003, plus 8 permanent GPS stations operating continuously beginning 1997. Observations across a 65-km wide area centered on the Wasatch fault indicate the principal horizontal extension rate of 24 ± 6 nstrain/yr with the direction nearly perpendicular to the fault. This strain rate corresponds to a horizontal displacement rate of 1.6 ± 0.4 mm/yr, accommodating ∼50% of the crustal deformation across the ∼200 km-wide eastern Basin-Range. Analysis of the spatial variation of the strain-rate field reveals that the strain accumulation is concentrated near the Wasatch fault, which suggests an abrupt transition in the horizontal deformation at the fault between the eastern Basin-Range and the Rocky Mountains. We employed a finite-strain model that accounts for simple-shear deformation of the hanging-wall to compare horizontal extension rates measured by GPS with vertical fault-displacement rates determined by geologic data. Our results suggest that the average Holocene strain-release rate is higher than the contemporary strain-loading rate for the Wasatch fault if the fault dips less than 30°W, but these two rates are consistent if the fault dips more steeply.