NA15: A new tomographic model of North America

Abstract:

We present a new S-velocity model of North America, with a special focus on the stable part of the continent and the Midcontinent Rift System (MRS) in particular. The occurrence of several rare M > 5 earthquakes in the central and eastern US, coincident with the passage of the USArray Transportable Array through this region and the deployment of the SPREE array over the MRS, provides unprecedented raypath coverage of stable North America. We fit regional S and Rayleigh wavetrains using the method of partitioned waveform inversion (PWI) (Nolet, 1990) to provide constraints on 1D path-average structure between each station-event pair. In a joint inversion for 3D structure, we combine these new constraints with waveform constraints from the NA07 tomographic model (Bedle and van der Lee, 2009) and Moho depth constraints from active-source and receiver function studies. The dense station coverage and abundance of relatively short (10-15 degrees) path lengths through high-Q stable lithosphere in our new waveform-fitting dataset permit us to fit the fundamental and higher modes and to fit up to frequencies of 0.1 Hz for some stations and events. This resolves finely-layered structure in the lithosphere, including a transitional layer between crust and mantle that is present below much of the stable continent and most pronounced in the northeastern US.