Borehole Seismic Monitoring of a Rock Massif Using Distributed Acoustic Sensing on an Undermined Territory

At the Verkhnekamskoe salt deposit, a monitoring system for the emergency area has been implemented, including a distributed acoustic sensing with a 6-km optical line and an active borehole source of elastic vibrations. Monitoring is performed using cross-well seismic survey. The use of a special cable containing straight and spiral fiber makes it possible to record both direct and refracted waves. Based on a comparison of wave fields, areas of change in the elastic properties of the massif are located and a quantitative assessment of such changes is given. The use of a large number of simultaneously recording channels makes it possible to achieve the required spatial resolution depending on the task. The low cost of fiber optic cable makes it possible to design its permanent installation in emergency areas with limited access. The proposed monitoring system can be used both to monitor the safety of the developed massif in problem areas, and to monitor the foundations of critical buildings and structures located in zones of accelerated subsidence of the undermined territory.