Incorporating Seismic Zonation into Earthquake Catalog Declustering

Seismic hazard assessment relies upon a complete earthquake catalog, necessitating a declustering procedure to filter out dependent aftershocks or foreshocks from the earthquake catalog. Traditional declustering approaches, such as the Gardner-Knopoff approach, utilize magnitude-dependent temporal and spatial windows to distinguish dependent aftershocks/foreshocks from independent mainshocks. However, these approaches may overlook regional seismic characteristics, which leads to missing out primary independent events occurring within the time and space window following a strong earthquake, particularly when the background rate is elevated. This study proposes a modified declustering approach that employs seismic zonation as an additional parameter in the declustering procedure. The proposed methodology investigates adjustments to the magnitude term within the filtering window criteria based on the correlation of the seismic zone of a designated event with other events. A comparative analysis with the classical Gardner-Knopoff approach is conducted to evaluate the effectiveness of the proposed approach. The findings show that using seismic zonation in declustering improves the depiction of the distribution of seismic activity and reduces the likelihood of filtering out primary independent mainshocks.