Detection of quarry and mine blast contamination in European regional catalogues

Abstract

Seismic catalogues often include man-made contaminations, that range from the changes in seismic networks operating in the region to the different processing of the data and to the inclusion of quarry explosions and marine shots. For example, the installation or closure of seismic stations produce an increase or a decrease in the detection of small events, whilst quarry blasts or mine explosions artificially enrich catalogues. Despite network operators’ best efforts to identify quarry blasts, it is easy to find these events in a catalogue, whereas the separation between explosion events and tectonic ones is a difficult task. Detection and removing of artificial events from a seismic catalogue should be the preliminary step in any analysis of statistical seismology. Wiemer and Baer (BSSA, 2000) proposed an algorithm, based on a statistical criterion, to identify and remove quarry explosions from catalogues. It is based on the observation that quarry blasts generally take place during daytime hours: the areas with a high ratio of daytime and night-time events are likely to be regions with quarry activity. In the first part of this work (Gulia, NH, 2010) we have modified the method and then tested it, using both a synthetic and a regional catalogue; in the second part the procedure has been applied to some of the European regional catalogues available on line. The comparison between the results obtained and the location of known quarries and mines for the analyzed catalogues confirms both the presence of non-natural events in seismic catalogue and the reliability of the methodology in identifying mining areas.