Seismic ground motion alerts for mines

Abstract

One of the objectives of seismic monitoring in mines is to detect strong and unexpected changes in the spatial and/or temporal behaviour of seismic parameters that could lead to rock mass instability and affect working places immediatelyx or in the short term. We present an influence based polygon-less method of detecting such conditions, taking into account the influence of ground motion generated by all available seismic events, regardless of their location, on a particular working place. The measures of influence are the peak ground velocity, PGV, and the cumulative absolute displacement, CAD, since their influences are moderated by the distance from the seismic source to the place of potential exposure. Both CAD and PGV are calculated for each point of interest from the ground motion prediction equation, GMPE, developed for a given mine. The CAD becomes CAID, i.e. cumulative absolute inelastic deformation, if the co-seismic strain, PGV\(/v_{S}\), exceeds the elastic threshold, e.g. \(10^{-6}\) for hard rock. Alerts and Alarms are triggered if the rates of CAID and/or its activity, ACAID, exceed predefined reference levels. Since they have different units, we normalise each by its reference level and at each time step select the one which is greater and call it the GMAP rating. All points that at a given time trigger an Alert define the exclusion zone and are monitored as time progresses.