Assessment of seismic tomographic models of the contiguous United States using intermediate-period 3-D wavefield simulation

Abstract

SUMMARYThe contiguous United States has been well instrumented with broad-band seismic stations due to the development of the EarthScope Transportable Array. Previous studies have provided various 3-D seismic wave speed models for the crust and upper mantle with improved resolution. However, discrepancies exist among these models due to differences in both data sets and tomographic methods, which introduce uncertainties on the imaged lithospheric structure beneath North America. A further model refinement using the best data coverage and advanced tomographic methods such as full-waveform inversion (FWI) is expected to provide better seismological constraints. Initial models have significant impacts on the convergence of FWIs. However, how to select an optimal initial model is not well investigated. Here, we present a data-driven initial model selection procedure for the contiguous US and surrounding regions by assessing waveform fitting and misfit functions between the observations and synthetics from candidate models. We use a data set of waveforms from 30 earthquakes recorded by 5820 stations across North America. The results suggest that the tested 3-D models capture well long-period waveforms while showing discrepancies in short periods especially on tangential components. This observation indicates that the smaller scale heterogeneities and radial anisotropy in the crust and upper mantle are not well constrained. Based on our test results, a hybrid initial model combining S40RTS or S362ANI in the mantle and US.2016 for Vsv and CRUST1.0 for Vsh in the crust is compatible for future FWIs to refine the lithospheric structure of North America.