P-wave tomography of potential convective downwellings and their source regions, Sierra Nevada, California

Abstract

Teleseismic P-wave tomography using the Sierra Nevada Earthscope Project (SNEP) deployment, older temporary deployments in the Sierra, and broadband stations from permanent and USArray Transportable Array (TA) stations was derived from starting models either lacking lateral variation (one dimensional [1-D]) or created from three-dimensional (3-D) surface-wave models. The use of multiple starting models permits examination of the robustness of different features while limiting the inherent ambiguities of teleseismic body-wave tomography. Our results confirm that mafic residuum of the Mesozoic Sierran batholith has been removed from the eastern Sierra north to at least 39°N. Low-wavespeed material near the Moho under the eastern Sierra is probably silicic lower crust and warm and possible melt-laden upper mantle. If the residuum remains in the upper mantle, there are three possible locations for it: a high-wavespeed (+∼5%) body extending down to ∼250 km near 36°N, 119.3°W termed the Isabella anomaly, an unusually high-wavespeed (to +10%) and shallow (top ∼40–50 km) anomaly at the south end of the Gorda slab near 40.5°N, 122.25°W termed the Redding anomaly, and a more ill-defined region of high wavespeeds in the crust to uppermost mantle (