USING GEODESY TO REVEAL DEFORMATION PARTITIONING AND TO PROBE THE LOWER CRUST BENEATH THE NORTHERN WALKER LANE

The northern Walker Lane (NWL) is a zone of complex strike slip and normal faulting that accommodates approximately 10 mm/yr of dextral transtension between the Sierra Nevada/Great Valley microplate and the Basin and Range province. New geodetic measurements are clarifying how NWL deformation is partitioned into distinct domains of strain accumulation that reveal the mechanisms behind this deformation. We will summarize results from the EarthScope Plate Boundary Observatory, and Mobile Array of GPS for Nevada Transtension, and other GPS networks that are providing new and improved constraints on the variation of rates, patterns and styles of deformation with the NWL. The GPS velocity field is both precise (most velocities have uncertainty between 0.2-0.5 mm/yr) and dense (with 5-20 km station spacing). Longer time series and improvements in processing techniques are enabling us to use the vertical component of GPS to constrain models of crustal deformation. We interpret the velocities with a combination of modeling approaches that allow us to estimate long-term motion of individual crustal blocks from short-term geodetic measurements, and provide the basis for comparison to geologic measurements of longer term deformation. We find that to within measurement uncertainty there is agreement between geologic and geodetic data for 10 out of 12 published slip rates. Two notable exceptions are the strike slip Mohawk Valley fault zone, where geodetic rates are greater, and the normal Genoa Fault, where geodetic rates are lower.

Deeply ingrained in the interpretation of GPS in terms of fault slip rates are the block modeling method, which accounts for interseismic fault locking, and the viscoelastic modeling, which accounts for postseismic relaxation from recent earthquakes. These techniques have linked geodetic measurements to properties of the lower crust and upper mantle, such as the depth to the brittle/ductile transition and the effective viscosities of rocks in the lower crust and upper mantle. We will present the predictions that our model makes for vertical motions in the NWL, compare them to GPS observations, and discuss the implications for the geometry of normal faults as they penetrate deep into the crust.