Geodetic constraints on contemporary deformation in the northern Walker Lane: 3. Central Nevada seismic belt postseismic relaxation

We combine horizontal Global Positioning System (GPS) velocities from a new compilation of published and new GPS velocities, results from an interferometric synthetic aperture radar (InSAR) study, and paleoseismic data to evaluate the postseismic response of historic earthquakes in the Central Nevada seismic belt. We assume that GPS velocity has contributions from time-invariant (i.e., steady permanent crustal deformation) and transient (i.e., time varying and associated with the seismic cycle) processes that are attributable to postseismic viscoelastic relaxation of the crust and upper mantle. In order to infer the viscosity structure of Basin and Range lower crust, η LC , and upper mantle, η UM , we apply three objective criteria to identify rheological models that fi t both geodetic and geologic data. The model must (1) improve the apparent mismatch between geodetically and geologically inferred slip rates, (2) explain the InSAR-inferred vertical uplift rate, and (3) not imply timeinvariant contractions anywhere in the extending province. It is not required for the postseismic deformation fi eld to resemble the time-invariant velocity fi eld in pattern, rate, or style. We fi nd that the InSAR and horizontal GPS velocities form complementary constraints on the viscoelastic structure, excluding different parts of the model space. The best-fi tting model has a lower crust that is stronger than the uppermost mantle, with η LC = 10 Pa·s and η UM = 10 Pa·s, a fi nding consistent with the majority of similar studies in the Basin and Range. The best-fi tting viscosity model implies that the majority of Central Nevada seismic belt deformation is attributable to postseismic relaxation, and hence that western Basin and Range time-invariant deformation north of 39°N latitude is more tightly focused into the northern Walker Lane than would be inferred from uncorrected GPS velocities. However, signifi cant deformation remains after correction for postseismic effects, consistent with Central Nevada seismic belt faults slipping at rates intermediate between the Walker Lane belt and the central Basin and Range.