A Crustal and Uppermost Mantle Model for the Conterminous United States

Abstract:

After more than eleven-years of progress of Earthscope/USArray transportable array (TA), nearly 2,000 seismic stations have covered the contiguous United States in a nearly regular grid and an unprecedented quantity of continuous seismic data have been accumulated. Based on the TA, many innovations in seismic imaging have been developed (e.g., the ambient noise tomography, eikonal/Helmholtz imaging methods, and the systematic observation of Rayleigh wave horizontal-to-vertical amplitude (H/V) ratios across large seismic arrays). These new imaging methods applied to the complete deployment of the TA provide the opportunity to reveal completely new views of the crust and uppermost mantle across the conterminous United States. In this presentation, we display a set of complementary observations for crustal and uppermost mantle imaging that includes: 1) Rayleigh wave dispersion information observed from ambient noise and teleseimic earthquakes, 2) P-wave receiver functions, and 3) Rayleigh wave H/V ratios observed from teleseismic earthquakes. We obtain these data and uncertainties systematically at each USArray/TA station across the US and invert them using a joint Bayesian Markov Chain Monte Carlo (MCMC) algorithm. The inversion results in spatially dependent posterior distributions of isotropic crustal and uppermost mantle shear wave speeds. We present and discuss the mean and standard deviation of these distributions. Compared with earlier earth models beneath the US notable improvements include: The topography of and contrast across the Moho are improved improved by joint inversion of surface wave dispersion with the receiver functions; Upper crust structures are sharpened by introducing the Rayleigh wave H/V ratio into the inversions; Depth-velocity trade-offs are greatly reduced as the velocity discontinuities are more accurately positioned. In addition, the resulting model displays a great variety and considerable richness of geological and tectonic features in the crust and in the uppermost mantle deserving of further focused and continued interpretation.