Listening To The Earth: An Unconventional Scientific Approach To Understanding Sub-surface Ground Conditions

Digitally recorded background ambient noise can be used to extract details regarding subsurface soil conditions. This unique methodology has been implemented to provide comprehensive assessments of geotechnical site conditions. Ambient noise is the persistent vibration of the ground in response to anthropogenic and natural causes. In many contexts, these background vibrations are classified as noise, and efforts are made to remove these signals from recorded data. However, these background vibrations also contain valuable information regarding the materials they travel through. The refraction microtremor (ReMi) technique separates these waves from noise recordings to determine soil shear-wave velocities. Interpolation of the closely spaced one-dimensional velocity-depth profiles along linear arrays allow two or three-dimensional velocity-versus-depth representations to be produced, thereby mapping lateral variations and extending subsurface characterisations between more expensive spot borehole measurements. ReMi technique provides a non- invasive and cost-effective way of estimating vertical soil/rock shear-wave versus depth profiles. This paper examines the contribution ReMi shear-wave velocity assessments can make towards enhancing subsurface geological and geotechnical models to mitigate risk from unforeseen ground conditions.