A comparison of teleseismic and regional seismic tomography west and east of the Rocky Mountains

We have measured teleseismic P and S relative delay times using waveforms from IRIS PASSCAL seismic arrays and EarthScope's Transportable Array sampling both western and eastern North America. Within some scatter, the S delays are consistently about 3 times stronger than the P delays. Delay times corrected for crustal structures from earthquakes with Mw>=6.0 show that the mantle beneath the US east of the Rocky Mountains is at least as heterogeneous as the mantle beneath the US west of the Rockies. A comparison with teleseismic S delay times predicted from a 3D model suggests that the relative contribution to these delays of the deep upper mantle is stronger in the east. Inversion of the relative teleseimic S delay times produced mantle velocity structure patterns familiar from previous studies. For example, a dipping, high velocity Juan de Fuca Slab, strong low velocities under Yellowstone and all along Snake River Plain, a relatively high velocity Colorado Plateau surrounded by low velocity arms, high velocity structures in the transition zone which could represent older fragments of Farallon Plate, and a strong velocity contrast across the Proterozoic-Paleozoic basement boundary on the eastern margin. Although focused on different wavelengths, the teleseismic model seems generally consistent with surface wave models such as NA04. However, important differences exist and we will report on our ongoing attempts to reconcile these differences through, for example, a joint inversion of teleseismic and regional S wave data for crust and mantle heterogeneity.