Love waves from local traffic noise interferometry

Abstract

Surface-wave interferometry on local scale usually aims at recovering Rayleigh waves. This is because of the predominant use of vertical component geophones in exploration seismology and the fact that Rayleigh waves occur for any given subsurface structure. On the other hand, Love waves are present only in layered media and require horizontal component geophones for their observation. As they depend on shear-wave velocity structure and density only, the analysis of Love waves provides a potentially powerful supplement to Rayleigh wave inversion. Perhaps surprisingly, recent studies show that low-frequency Love waves (0.05–0.1 Hz) excited by the interaction of ocean waves with the ocean floor (the Earth's microseism) can be recovered by interferometry, and that their S/N is high compared to Rayleigh waves (Lin et al., 2008). On a regional scale, Jay et al. (2012) analyzed the ambient noise field in a volcanic region and found that Love waves with frequencies of about 0.3 Hz are observed more clearly than corresponding Rayleigh waves. In this article, we show that Love waves in the frequency band of 1.5 to 5 Hz can be obtained from local noise interferometry, and that they are of comparable S/N as Rayleigh waves. Thus they may also be used to constrain the near-surface structure.