Rayleigh wave phase velocity models for gravitational wave detectors using an array of nodal sensors

Abstract

Array studies of ambient seismic noise have gained much importance in recent years for the purpose of classifying noise sources corresponding to different frequency bands. Stehly et al. (2006), Snieder et al. (2009), Wapenaar et al. (2010), have also demonstrated useful applications of using ambient noise recordings for surface wave tomography. Seismic motions generated by natural and artificial sources propagate through the subsurface both in the form of body and shear waves. But the major contribution to the seismic noise field is in the form of Rayleigh and Love waves (Haubrich et al., 1963), especially at shallow depths. In the context of gravitational wave detectors, such displacement of the subsurface couples with the suspended elements of the detector through gravitational forces of attraction and is referred to as Newtonian noise. In order to subtract this noise, it is necessary to understand the sources of seismic noise near the detectors and the propagation characteristics. Hence, an optimal seismic array was designed and a passive seismic survey was carried out at the Advanced Virgo gravitational wave detector in Italy. Easily deployable 5 Hz vertical component wireless geophones were used for continuous acquisition of the seismic noise.