Effect of viscoelastic postseismic relaxation on estimates of interseismic crustal strain accumulation at Yucca Mountain, Nevada

Abstract

We estimate the long‐term crustal strain rate at Yucca Mountain (YM), Nevada from GPS velocities taking into account viscoelastic relaxation following recent earthquakes to remove bias associated with transient deformation. The YM data reveal postseismic relaxation in time series non‐linearity and geographic variation of the transient signal. From the data we estimate best‐fitting lower crust and upper mantle viscosities of 1019.5 Pa s and 1018.5 Pa s, respectively. Once the relaxation model predictions are subtracted from the data, the long‐term shear strain accumulation rate is between 16.3 and 25.1 nanostrains/year (ns/yr) to 99% confidence, a range much larger than the formal uncertainties from GPS measurement. We conclude that 1) a Maxwell viscoelastic model cannot explain all the deformation observed at YM, 2) uncertainty in viscosities dominates uncertainty in YM strain rates, and 3) the effects of large, recent earthquakes must be accounted for in seismic hazard studies using GPS.