Body-wave reconstruction from ambient seismic noise correlations in an underground mine Gerrit Olivier 1 , Florent Brenguier 2 , Michel Campillo 2 , Richard Lynch 3 , and Philippe Roux 2 ABSTRACT The reconstruction of seismic Green’s functions from correla- tions of ambient seismic noise has recently developed as a prom- ising approach for exploring the earth’s interiors without the requirement of costly active seismic sources. This approach is widely used for imaging the crust at a kilometer scale. However, few studies report noise-based Green’s function reconstruction at smaller scales in industrial environments. We have investigated the possibility of constructing seismic Green’s functions between sensors in an active underground mine (Garpenberg, Sweden) by crosscorrelating seismic noise generated by mining activities. We have determined with realistic numerical simulations that the mining excavations in an underground mine lead to a regime of strong scattering, which is favorable for constructing seismic Green’s functions by crosscorrelating seismic noise. One month of continuous data was recorded by 18 seismic sensors located more than 1 km below surface. A variety of broadband (10– 3000 Hz) seismic sources were present, but the seismic wave- fields are directional and often monochromatic, so that the con- ditions for constructing Green’s functions by crosscorrelating ambient seismic noise were not ideal (isotropic illumination and spectrally white). We developed a stacking scheme that dismissed data during periods when the seismic noise was dominated by monochromatic signals or when noise sources were not in station- ary phase locations. Estimates of the seismic Green’s functions were retrieved for a broad frequency range (20–400 Hz) for almost all of the correlation pairs when we used the selective stacking scheme. We used the direct body waves present at low frequencies (less than 100 Hz) in the reconstructed seismic Green’s functions to invert for the 3D S-wave velocity structure of the mine. Our results revealed the existence of a high-velocity zone and a low-velocity zone that corresponded with known ore bodies. INTRODUCTION Crosscorrelating ambient seismic noise can be used to construct the seismic Green’s function between sensors pairs, effectively turn- ing one of the sensors into a virtual source (Shapiro and Campillo, 2004; Sabra et al., 2005b; Campillo, 2006; Stehly et al., 2008). Over the past decade, Green’s functions, constructed by crosscor- relating ambient seismic noise, have been predominantly used to im- age the upper crustal structure of the earth (Sabra et al., 2005a; Shapiro et al., 2005; Moschetti et al., 2007; Lin et al., 2013a, 2013b; Boué et al., 2014). The vast majority of ambient noise tomography studies have been performed with surface waves because the sensor arrays used for these studies are located at the surface and the seismic noise is dominated by the surface waves emanating from the inter- action of the ocean with the solid earth (Webb, 1998). Constructing body waves by crosscorrelating ambient seismic noise has proven to be much more difficult (Forghani and Snieder, 2010), but there are a few notable examples in which body waves have been extracted from ambient seismic noise (Roux et al., 2005; Zhang et al., 2009; Nakata et al., 2011; Boué et al., 2013). To construct full Green’s functions between sensors by crosscor- relating seismic noise, sensors should be surrounded in all directions by a large (theoretically infinite) number of spectrally white sources (Lobkis and Weaver, 2001), or spectrally white sources should only be located in stationary phase locations (Roux and Kuperman, 2004). Manuscript received by the Editor 29 June 2014; revised manuscript received 9 December 2014. 1 Universite´ Joseph Fourier, Institut des Sciences de la Terre, Grenoble, France and Institute of Mine Seismology, Kingston, Tasmania, Australia. E-mail: gerrit .olivier@imseismology.org. 2 Universite´ Joseph Fourier, Institut des Sciences de la Terre, Grenoble, France. E-mail: florent.brenguier@ujf-grenoble.fr; michel.campillo@ujf-grenoble.fr; philippe.roux@ujf-grenoble.fr. 3 Institute of Mine Seismology, Kingston, Tasmania, Australia. E-mail: richard.lynch@imseismology.org. © 2015 Society of Exploration Geophysicists. All rights reserved. 1 GEOPHYSICS, VOL. 80, NO. 3 (MAY-JUNE 2015); P. 1–15, 16 FIGS. 10.1190/GEO2014-0299.1