Integrated seismic measurement techniques to determine the velocity distribution near underground drifts at the Sanford Underground Research Facility (SURF)

The Sanford Underground Research Facility (SURF) is located in the central part of the USA in a former deep gold mine. The primary purpose of the facility is to provide a host for physics experiments that require shielding from cosmic radiation, but it also offers an excellent deep testbed for geological and geoengineering experimentation. The facility is expected to be in operation for tens of years and it already has experienced an extended history as a mining operation. Determination of seismic velocities of the rock can provide information regarding the current geomechanical condition of the host rock and also will provide information for the design of geophysical monitoring in support of future hydraulic fracturing experiments. Measurement of seismic velocities on recently acquired core produced reproducible seismic profiles with lower seismic velocities close to a drift that is located 1.5 km below surface and that has been open for over 40 years. These core measurements, however, were acquired on unconfined cores, therefore, a series of seismic surveys to determine in situ velocities were undertaken in order to evaluate the effect of stress. These seismic surveys produced inferred seismic velocity profiles that were similar to those derived from core measurements, although with greater seismic velocities due to high rock stress.