Statistical analysis of earthquake catalogs for seismic hazard studies around the Karliova Triple Junction (eastern Turkey)

A complete and comprehensive earthquake catalog is a substantial input to do probabilistic seismic hazard analysis. The Karliova triple junction (eastern Turkey) is characterized by an active seismicity mostly in the shallow crust. Origin times, earthquake locations, and magnitudes reported by the Kandilli Observatory and Earthquake Research Institute, Bogazici University (KOERI) and three international agencies (ISC, IRIS and EMSC) in the region bounded by latitudes 37.5 degrees and 40.5 degrees N and longitudes 37.5 degrees and 42.5 degrees E have been gathered in order to quantify the seismicity around the study area and calculate associated seismic parameters. The Magnitudes of completeness (Mc) and Gutenberg-Richter (GR) recurrence parameters (a- and b-values) have been estimated. The same Mc value of 2.7 has been obtained for all catalogs. After 2014, all earthquakes with magnitudes higher than 2.0 are reliably recorded. However, the b-value varied from 0.97 to 1.28. High b-value anomalies mostly for earthquakes with shallow depths (5-15 km) have been observed. A relatively lower bvalues are found at depths <5 km. The most probable largest annual earthquakes are around Mw = 5.8. The seismic hazard parameters i.e. the maximum regional magnitude mmax, mean seismic activity rate lambda, the slope of the frequency-magnitude Gutenberg-Richter relationship, and the beta value (bln(10)) have been estimated. Using the Bayesian model for the earthquake occurrence in time and earthquake magnitude, which incorporates seismic information from historical and instrumental catalogs, the hazard parameters are presented in terms of the probability of exceedance for 1- 10- 50- and 100-year return periods with a b-value equal to 1.19 and mmax equal to 8.05. The highest probability of earthquakes, which may occur in an interval of 50 years is estimated as Mw = 7.0. The average recurrence interval of earthquakes with magnitudes 6.7 and 7.8 (the maximum observed magnitudes at KOERI catalog and instrumental earthquakes in the region, respectively) are -27 and -488 years.