Abstract:
Spectral analysis of seismic waves is one of the most important origins of information for the earthquake sources. In this study are presented P- and S-waves spectra of the earthquakes from two seismic swarms: the April 2009 swarm located in the vicinity of the city of Kardzhali and the 2014 swarm located near the city of Plovdiv. The database used in the study is compiled using digital data from the Bulgarian Seismological Network – NOTSSI. Displacement spectra are generated for P- and S- waves to estimate some of the source parameters, such as seismic moment, stress drop, source radius and moment magnitude. Earthquake source parameters are estimated applying Brune model. The source parameters are estimated for 10 earthquakes: five earthquakes of the sequence near the city of Kardzhali and five earthquakes of the sequence near the city of Plovdiv with magnitude in interval 2.7 ÷ 4.1. The estimated stress drop values are within the expected range. The 2009 swarm have lower values of the stress drop, in comparison with 2014 swarm.