Paleoseismology of the Ganos segment; the western extend of the North Anatolian Fault (Turkey)

Abstract

The Ganos fault that ruptured on 9 August 1912 (Mw: 7.4) is the westernmost inland segment of the North Anatolian fault (NAF). Here, the Ganos fault is bounded at its two tips with offshore faults segments, in the Sea of Marmara to the east and the Gulf of Saros to the west in the North Aegean Trough. Therefore, the paleoseismology of the 45-km-long inland fault is of importance to the seismic hazard analysis related to offshore active faults and in particular for the seismic gap in the Marmara Region. Earlier studies have established an earthquake chronology for the western and eastern inland tips of the Ganos fault. Here, we extend the paleoseismic studies toward the central segment. Three trenches at Yörgüç have revealed evidence for two faulting events, possibly post-1669 CE ±30 years, which can be correlated to the 1659 or 1766, and the 1912 historical earthquakes. At Yeniköy, we determined an offset of 46 ± 1 m and 47 ± 1 m on a stream channel and a ridge-crest, respectively. In two trenches we determined two faulting events for the last 1000 years and seven events for the last 3500 years. In trench T5, the base of the displaced stream channel provides a calibrated date of 829–591 BCE. Using the 46 ± 1 m right-lateral displacement, we calculate a slip rate of 16.9 ± 0.7 mm/year for the last 2732 ± 119 years. A combined analysis with earlier paleoseismic studies on the Ganos fault suggests that the historical earthquakes of 1912, 1766b or 1659, 1354 or 1343a, and 1063 ruptured the entire inland fault section. In such a case, the recurrence interval for this section of the NAF corresponds to 283 ± 81 years. Combining earlier estimations, we suggest an average slip rate of 17.1 ± 0.9 mm/year for the last 2700 years and observe a characteristic slip behavior of 4.5 to 5 m per event for this section of the North Anatolian plate boundary fault.