Local amplification of Rayleigh waves in the continental United States observed on the USArray

• We develop a new method to determine local amplification of surface waves.
• We determine amplification factors across the USArray footprint.
• Observed local amplification is coherent across the array at a range of periods.
• Variations in local amplification reach values of +/−+/− 10% at a period of 125 s.
• Amplification factors contain information about local elastic structure.

We develop a method based on ratios of amplitudes measured at adjacent stations to determine local amplification of surface waves across an array of seismic stations. We isolate the effects of local structure from those of the earthquake and propagation by systematic averaging of ratios corresponding to many sources. We apply the method to data recorded on the USArray for the years 2006–2011 and determine amplification factors at each station of the array for Rayleigh waves at periods between 35 s and 125 s. Local amplification factors are spatially coherent and display variations of ±10% at a period of 125 s and greater variations at shorter periods. Maps of local amplification exhibit spatial correlation with topography and geologic structures in the western and central United States. At long periods, the observed amplification factors correlate well with predictions from a regional crust and mantle model of North America. At short periods, correlations are weaker, suggesting that the local amplification factors can be useful for constraining shallow structure better.