Strain and velocity across the Basin and Range derived from 15-ka fault slip rates: Implications for reconciling geologic and geodetic observations across the Walker Lane

Abstract:

We calculate average strain and velocity across the Great Basin, Basin and Range, western USA, over the past 15 ka from fault slip rates derived from paleoseismic studies, and we compare the resulting velocity field to GPS velocities relative to North America. Strain and velocity derived from fault slip rates show a concentration of right-lateral shear and extension in the western Great Basin (Walker Lane), with modest straining across the central Great Basin, and a zone of higher strain in the eastern Great Basin. The pattern of regional strain release derived from 15-ka fault slip rates is similar to the pattern of modern GPS velocities. In the Walker Lane, however, the magnitude of velocities from fault slip rates is lower than from GPS. The regional approach implies that the mismatch is not due to crustal block rotations or transient strain rates. The missing shear is likely due to distributed strain, slip on unidentified minor faults, and slip in moderate size earthquakes invisible to the paleoseismic record. We show that the observed strain concentration in the western Great Basin is consistent with a Sierra Nevada block that is more rigid than the surrounding lithosphere of nonlinear rheology, concentrating strain east of the rigid block in the Walker Lane. Together, these results suggest that (1) regional strain release patterns have been approximately constant over the past 15 ka, (2) the paleoseismic record is missing evidence of strike slip on faults in the Walker Lane, (3) seismic hazard may be higher than suggested by fault slip rates alone, and (4) treating the western U.S. as a thin viscous sheet with the Sierra Nevada block as a rigid boundary provides a consistent history of continuous deformation in the Walker Lane over decadal, millennial, and Neogene timescales.