PdS Receiver Function Imaging of the U.S. West of the Mississippi

Using USArray data we have made continuous PdS Common Conversion Point Stacked image volumes extending from the Pacific coast to approximately the Mississippi River. The 3D image volume was formed by stacking 93,599 receiver functions from 505 teleseismic earthquakes recorded at 1582 USArray and other broadband stations. We used iterative time domain deconvolution and water-level frequency domain deconvolution to form 1s and 2s receiver functions, which were stacked in 4 different volumes. The data were repositioned laterally and in depth using a hybrid velocity model made by combining Crust2.0 (Bassin et al., 2000) and finite-frequency P and S wave tomography models (Schmandt and Humphreys, 2010; and Schmandt, unpublished). Here we concern ourselves with aspects of the lithospheric structure between the Rocky Mountain Front and the Mississippi, and describe a few notable features: Like previous studies we find that the crust of this region is generally between 40 and 50 km thick. Both the crust and lithospheric mantle show thinning under the easternmost Jemez Lineament where it crosses the Rocky Mountains and enters the Plains. Much of the Great Plains and part of the Midwest is underlain by a vast variable thickness high velocity crustal layer that extends from ~33N in the east to 35N at 105W, runs NNE east of the Rocky Mountain Front, and then NE toward Lake Superior. It lies roughly north of the Grenville Front, underlying much of the Yavapai-Mazatzal and Superior, and possibly parts of the Trans-Hudson provinces. The layer reaches a maximum thickness of about 25 km near its geographic center, and has an average thickness of about 15-20 km. South of the Grenville Front the layer dies out. Profiles across the Grenville Front into coastal Texas and Mexico show a step-wise decrease in crustal thickness from 48 km to 43 km to 39 km.