Discriminating Earthquakes from Quarry Blasts Based on ShakeMap Ground-Motion Parameters

We use ShakeMap ground-motion parameters from small seismic events in the western Alberta region to develop a reliable seismic discriminant that can be used in an automated procedure to distinguish blasts from earthquakes. In comparison with earthquakes, quarry blasts have higher vertical-to-horizontal (V/H) ratio of ground-motion parameters at high frequencies (similar to 8-15 Hz) and at close distances (< 100 km). The optimal ground-motion discriminant is the V/H ratio at 10 Hz. The differences in ground motions between blasts and earthquakes become obscured with increasing distance. We combine the ground-motion-based discriminant with a temporal and spatial clustering approach to develop an automated quantitative discrimination procedure that can be applied at regional distances. The proposed approach provides similar to 100% effective discrimination between the earthquake cluster in Rocky Mountain House and the quarry explosions in the Keephills mining cluster in western Alberta. Having a reliable automated process that is based on the multivariate discrimination is useful for the compilation of reliable seismicity catalogs in near-real time.