“…Such studies now routinely extract surface waves from ambient microseismic noise (e.g., Lin et al, ; Shapiro et al, ). Interferometry has also been applied in attempts to extract body waves from ambient noise (e.g., Draganov et al, ; Lin et al, ; Roux et al, ; Ryberg, ; Zhan et al, ), from discrete sources including in exploration seismology (e.g., Schuster, ; Wapenaar et al, ) and from local or teleseismic earthquake signals (e.g., Kim et al, ; Nakata et al, ; Ruigrok & Wapenaar, ). However, distinct boundaries have commonly been difficult to image in the body waves from these studies, particularly at depths of more than a few kilometers, so the method is not commonly used for such imaging.…”