Simultaneous Inversion of Interpolated Receiver Functions, Surface-wave Dispersion, and Gravity Observations for Lithospheric Structure Beneath the Eastern United States

Abstract:

The unprecedented high-quality seismic data from Earthscope’s Transportable Array provide us a great opportunity to investigate the subsurface structure beneath North America. Even with such a fine network, tightly constraining the 3D lithospheric structure is a challenge. Integrating complementary geophysical observations in simultaneous inversions has produced promising results. We have developed a receiver-function wavefield interpolation/smoothing method to enhance the complementariness of receiver functions and surface-wave dispersion. Combining information from adjacent seismic stations suppresses poorly sampled and difficult-to-interpret back-azimuthal variations and allows the stable extraction of the key features in the receiver-function wavefield. The interpolated receiver functions are inverted simultaneously with Rayleigh-wave phase and group velocities and Bouguer gravity observations to produce a robust estimate of the broad 3D shear-wave speed variations beneath the eastern United States. P-wave velocities and density variations are related to shear-speed using empirical velocity ratios and relations. We constrain the 3D variations to be laterally and vertically smooth. Application of the same methods to the western conterminous United States resulted in velocity images that are consistent with published models on the first order. With the completion of the Transportable Array deployment in the northeast US, the seismic dataset beneath the eastern U.S. region is complete. Preliminary inversions contain expected near-surface low shear-wave speeds associated with large basins and coastal regions and thicker crust beneath the interior compared with the coastal regions. Speeds in the upper mantle are generally typical, but the model includes several regions of relatively slow mantle beneath the northern Mississippi Embayment, the east coast, and beneath New England.