Effect of Higher-Mode Interference on Measurements and Models of Fundamental-Mode Surface-Wave Dispersion

Observations of fundamental-mode Love- and Rayleigh-wave dispersion provide some of the strongest constraints on the elastic structure of the upper mantle including lateral variations in radial anisotropy. However, estimates of the phase speed of fundamental-mode Love waves can easily be contaminated by the presence of overtones with similar group speeds if special care is not taken in the measurement procedure. Here, we evaluate the ability of modern measurement techniques to obtain unbiased fundamental-mode dispersion estimates and examine maps constructed using such data for artifacts caused by overtone contamination. We focus on the measurement approach of Ekstrom et al. (1997), which has been used to produce large datasets employed by many authors and which shares key characteristics with other commonly used approaches. We find that errors introduced by overtone interference are generally small in individual measurements compared with typical signal amplitudes. We find no systematic bias in the resulting phase-velocity models and conclude that recently observed differences in radial anisotropy beneath continents and oceans are unlikely to result from measurement biases caused by higher-mode interference.