Evaluation of ambient noise levels at selected digital stations of the Bulgarian National Seismological Network (BNSN)

An evaluation of the ambient seismic noise for five digital broadband BNSN (Bulgarian National Seismological Network) stations is presented. The Power Spectral Density (PSD) and Probability Density Function (PDF) are calculated using data from winter month (February 2006) when high noise level is observed. The method applied allows using data contaminated with earthquakes and other “disturbing” signals due to their low-level probability of occurrence. Selection of seismic stations was done in order to comprise different site conditions, which highly influence the ambient seismic noise. The results obtained are of substantial importance for evaluation of the existing seismic broadband station performance as well as for the site selection for new stations.