Contamination of seismicity catalogs by quarry blasts: An example from İstanbul and its vicinity, northwestern Turkey

Scientists have proposed two fault systems of different ages in the Sea of Marmara: the Thrace-Eskişehir Fault Zone of Early Miocene–Early Pliocene age and the North Anatolian Fault Zone of Late Pliocene–Recent age. Different seismicity rates and extensions of these faults onto land near İstanbul have been suggested. One of the reasons for these differences is the contamination of seismicity catalogs by seismic events from quarries operated in İstanbul and its vicinity, including Gaziosmanpaşa (Cebeci and Kemerburgaz), Çatalca, Ömerli, Gebze, and Hereke.In this study, we investigated waveforms of 179 seismic events (1.8 < Md < 3.0) from the KOERI, NEMC digital database. We determined differences between earthquakes and quarry blasts based on time- and frequency-domain analyses of their seismograms (amplitude peak ratio, power ratio, and spectral amplitude ratio) and used these differences as discriminants. The results of this study indicate that 15% and 85% of the investigated seismic events are earthquakes and quarry blasts, respectively.