Abstract
While the first-order Born approximation is increasingly being used in many seismic tomography efforts, its domain of validity to forward model seismic waveforms has not been quantified in the context of current 3-D earth models yet. We here address this issue by comparing teleseismic synthetic surface waveforms calculated using the Born approximation with spectral element method solutions for a variety of realistic global 3-D earth models. We find that the Born approximation has a very limited domain of validity when applied to seismic waveforms. Specifically, it can only accurately model the phase (amplitude) of surface waveforms for source-receiver paths leading to time shifts smaller than about 15 per cent (5 per cent) of the wave period considered. These conditions usually occur in earth models as S20RTS or S40RTS combined with a homogeneous crust for periods longer than T similar to 80-90 s. For models with stronger heterogeneity and/or realistic 3-D crustal structure, only the phase of waveforms with periods longer than similar to 120-130 s can be accurately modelled with the Born approximation.