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

Abstract

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.