| North American mantle velocity structure was studied by seismic tomographic inversion and mineral physical modeling. A new software package named AIMBAT was developed for efficient and robust measurements of teleseismic P and S wave delay times from large-volume seismic data. Using AIMBAT, a total of 131,978 P and 130,388 S delay times were measured from 667 teleseismic earthquakes recorded by about 2000 broadband seismic stations which are mainly EarthScope's USArray stations. Delay times corrected for effects of event-side heterogeneity and station-side crustal structure suggest that the mantle beneath the eastern US is as equally heterogeneous as the mantle beneath the western US. This heterogeneity results from the asthenosphere beneath the western US and the lithosphere beneath the eastern US, which contribute most to the total delay time signatures. Geological binning of observed delays further suggests that mantle heterogeneity is not correlated with the timing of tectonic activity.;Three-dimensional P and S velocity models XL13P and XL13S for the North American mantle were inverted from teleseismic P and S wave absolute delay times, respectively. Model NA13 improves XL13S by adding existing surface waveform-fit data and independent Moho depth point constraints in a joint inversion, in which the merits of body wave's lateral resolution and surface wave's vertical resolution are combined. Images of the subducting Juan de Fuca and Gorda slabs are improved by NA13, in which the slabs are no longer connected to seismic stations at the surface. Strong low velocity anomaly of up to -14% for V s beneath the Snake River Plain and Yellowstone is not explained by pure thermal effects and partial melting is necessary. Continuous but deflected plume conduits are observed. Sharp contrasts in seismic velocities are imaged across the Rocky Mountains. The velocity contrast within the mantle deviate from the surface geological boundaries as also suggested by the delay time analyses. The western edge of the North American craton shows complex variations.;A comprehensive thermoelastic database for major mantle minerals has been compiled from mineral physics experiments to quantify the effects of water and iron contents on the elastic properties. Finite strain velocity modeling supports that hydrous iron-bearing olivine polymorphs have elevated moduli pressure derivatives, which are subjected to large measurement uncertainties. Compared to a dry pyrolite mantle, addition of more than 1 wt.% H2O to the transition zone provides better fits to the velocity range of the globally averaged seismic models. Significant hydration within the transition zone is possible. Partial derivatives of seismic velocities with respect to temperature, water and iron contents are calculated as guidance for interpreting velocity anomalies from seismological observations as thermal and/or compositional variations. |
