Abstract:
The main goal of this study is to evaluate ambient seismic noise at the Bulgarian National Digital Seismic Network (BNDSN) stations equipped with new broadband seismometers. In order to compare the performance of the network against international standards a detail analysis of the noise was performed using method and software that are applied in the international practice. To estimate the distribution of power spectral density (PSD) of the noise over the wide frequency band probability density function (PDF) was calculated. Annual, frequency, seasonal and diurnal analyses were performed. The levels of the ambient seismic noise were determined and the full range of the factors influencing the quality of the data and the performance of a seismic station were analyzed. The estimated PSD functions were compared against two global models (NHNM and NLNM) for high and respectively low noise levels. The results show that estimated PSDes fall within NLNM and NHNM for all of the BNDSN stations and the Bulgarian seismic stations belong to the medium noise level stations worldwide. It has been shown in the study that the seismic noise analysis is very useful tool for evaluation performance of the BNDSN seismic broadband stations.