COMPARISON OF FOUR EARTHQUAKE DECLUSTERING METHODS APPLIED TO THE HOMOGENEOUS EARTHQUAKE CATALOG FOR BULGARIAN AND ADJACENT REGIONS (1981-2019) AND COMPARISON OF THE RESULT

Composite Abstract: The spatial-temporal distribution of seismic activity in Bulgaria and adjacent regions was studied using a homogeneous earthquake catalog from 1981 to 2019. The catalog comprised 1024 earthquakes with Mw≥3.2, collected from the Bulgarian Seismological Network. To isolate primary and secondary shocks and background events, four declustering methods were employed: Gardner-Knopoff (1974), Gruenthal (pers. Comm.), Reasenberg (1985), and Urhammer (1986). The catalog consists of earthquakes in Bulgaria and the surrounding areas (41° – 44°.6N, 22° – 30° E; 1024 events), with a completeness magnitude Mc = 3.2. After declustering, the number of events in the final catalogs varied for each method. The cumulative distribution was analyzed, and mainshocks, foreshocks, and aftershocks were identified for specific events. The study emphasized the importance of declustering in seismic analysis but recognized limitations in data completeness, quality, and algorithmic constraints. The results provided valuable insights for seismologists and specialists studying seismic phenomena and seismic risk assessment.The methods were applied using the ZMAP software.