Microseismic monitoring to assess rock mass damaging through a novel damping ratio-based approach

Monitoring rock mass damaging through the analysis of seismic records is an affirmed tool to manage rock fall risk in view of mitigation strategies. This study proposes a novel approach, named DAmping RaTio Anomalies Monitoring (DaRtAM), to detect the rock mass damaging by measuring variation over time of the damping ratio related to in-situ recorded vibrational events. Although damping-based damage detection techniques are well known for structural monitoring, only few applications exist for rock mass damage investigation not including in- situ long term rock mass monitoring. Here, a three-month-long seismic dataset recorded on a rock wall (Acuto Field Laboratory) by means of six one-component accelerometers was analysed with a STA/LTA algorithm that allowed to extract 19013 vibrational events. The damping ratio of the signals was derived as a function of frequency, averaged in a daily time window and analysed over time to output short-term anomalies and long- term trend. Although the limited time period analysed did not allow to observe significant trend variation of the damping ratio, 131 short-term anomalies were found in the collected seismic records. As it results from this study, the proposed approach is suitable for detecting rock mass damaging and, as a future perspective, will be applied to yearly-lasting vibrational datasets. This approach may be more effective with data acquired in environments characterised by recurrent forcings, such as coastal cliffs forced by sea and wind storms, rock walls stressed by thermal cycles, quarry walls involved in human activities or rocky trenches close to roads and railways.