SKS Splitting Analyses From The Sierra Nevada EarthScope Project: Insights Into Lithospheric Foundering

Foundering of ultramafic and mafic composition mantle lithosphere has been used to account for processes in both continental tectonics and the development of continental crust from a more mafic mantle. Recent work in the Sierra Nevada indicates that eclogite and peridotitic mantle lithosphere beneath the range since the Mesozoic were removed from at least the southern portion of the range by about 3.5Ma and now sink beneath the Central Valley. The ongoing SNEP (Sierra Nevada EarthScope Project) seismic deployment is intended to understand better the extent to which the Sierra Nevada batholith has lost its garnet rich root. The deployment consists of ~75 broadband installed in two phases extending from ~37N to 40.5N at approximately 25km station spacing. This deployment represents a significant densification of the EarthScope/USArray Transportable Array (TA) network. We analyze S and SKS phases for shear-wave anisotropy from SNEP, TA, and other broadband stations in the region to estimate splitting parameters (dt, phi) using standard methodology. Preliminary results show that splitting in the region is moderate to high, with dt >1s at most stations. We note a general shift in the polarization direction of the fast shear waves from approximately E-W, to more NE-SW, from the western foothills, across the Central Valley. Crustal anisotropy is insufficient to explain our results, which have important implications for uppermost mantle flow patterns beneath this region of recent lithospheric foundering.