World Journal of Research and Review (WJRR) ISSN:2455-3956, Volume-6, Issue-3, March 2018 Pages 38-61 North Anatolian Fault Zone, Northern Turkey: Empirical Equations and the Changes in Some Kinematic Characteristics Mehmet UTKU · İzmit via Düzce, Akyazı (Adapazarı), Sapanca Abstract- Monitoring the seismological development of a (Adapazarı), Gölcük (İzmit) and Hersek (İzmit), meets seismotectonic source is important to know the future the Ganos (Gaziköy, Tekirdağ) Fault to the north of the behavior of the source concerned. The North Anatolian Marmara Sea, and is conveyed to the Aegean Sea. Its Fault Zone is one of the important seismotectonic sources in other branch again reaches the Ganos Fault via Geyve the world. The seismic moment-magnitude relations were computed according to the macroseismic and instrumental (Adapazarı), İznik (Bursa) and Gemlik (Bursa) routes after Bolu, in the south of the Armutlu Peninsula and by observations of 29 earthquakes with mb,S 4.8 that occurred in the North Anatolian Fault Zone in the 1909- passing through the Marmara Sea almost centrally. 2000 period. The relations of seismic moment for this Another branch of it progresses on land in the south of tectonic structure according to the surface wave magnitude the Marmara Sea and extends to the Aegean Sea via the and according to the fault area and the change in stress Biga Peninsula. drop are the other seismological characteristics addressed in this study. Depending on the other parameters within the So far, many studies have been made with respect to scope of the study, the threshold magnitude value and the the NAFZ [38], [37], [39], [23], [36], [17], [56], [54], mean slip rate for the visible fault on the ground surface are [55], [7], [6], [5], [16], [27]. Mean displacement computed as 6.2 (Ms) and 2.2 cm/year, respectively. velocities of 3 cm/year or 4 cm/year and even up to 11 According to the 13958 earthquakes with M 3.0 that cm/year were found in these studies according to the data occurred in the North Anatolian Fault Zone in the period then [4], [35], [11]. Of them, a similar study which most between 11/24/0029 (29 A.D.) and 12/31/2014, the return closely fit the information obtained from the observation period of a possible major earthquake to be generated by this zone is 250 years at the most. The a- and b- values results and from the instrumental data was made by which characterize the Zone are 4 and - 0.8 on an average, Canıtez and Ezen (1973) with 8 earthquakes with mb respectively. 6.0 in the 1900-1971 period, and it calculated the stress When the results in this study – obtained according to the drops of 39 earthquakes by deriving statistics. Later on, 91-year data process and the 101-year evaluation process – the 8 earthquakes with M 6.0 between 1939 and 1967 are compared with the results known from the previous s studies, the latest results appear more reliable both in terms were used by Ezen (1981) to estimate various relations of the length of the process considered and the quality of the between source parameters and magnitude. Some 7 data used. When the behavior of the seismotectonic source earthquakes were common in both studies. Barka and concerned is monitored depending on this, it is seen that Kadinsky-Cade (1988) investigated the segmentation of some seismological characters remained stable, while some two major strike-slip fault zones in Turkey. Wells and of them changed. Coppersmith (1994) compiled 421 historical earthquakes Index Terms - NAFZ, Empirical equations, threshold magnitude, stress drop, seismic moment, slip rate, a- values, worldwide. By using 244 earthquakes selected, they b- values. developed the empirical relationships among various I. INTRODUCTION source parameters such as moment magnitude, surface The North Anatolian Fault Zone (NAFZ) is an essential rupture length, subsurface rupture length, downdip tectonic structure which plays the leading role in the rupture width, rupture area, and maximum and average regional tectonics thanks to the intracontinental transform displacement. fault identity it has maintained so far [53], [52], [8]. It is Of the studies in recent years, Ambraseys and Jackson an approximately 1400-km-long seismotectonic source (2000) deal with the seismic activity that occurred in the that originates from the surroundings of Karlıova Marmara Sea in the last 500 years. Accordingly, it is (Bingöl) in the east, continues with three branches after stated that an evident seismic activity was experienced in Niksar (Tokat), Ladik (Samsun), Kargı (Çorum), Tosya the Marmara Region in the 20th century; however, (Kastamonu) and Bolu, crosses the Marmara, and reaches throughout these 500 years, only the 18th century the Aegean Sea. The NAFZ, which last gained currency displayed a comparative seismic activity that also had with the August 17, 1999 (Mw=7.4) Gölcük (İzmit) processes which did not generate earthquakes with a earthquake and the November 12, 1999 (Mw=7.2) Düzce magnitude of 6.8 (Ms) and greater. Moreover, two (Bolu) earthquake, has a branch that crosses the Gulf of regions with late Quaternary faulting are mentioned, namely the north-west of the Marmara Sea and the southern branch of the North Anatolian Fault to the east · Mehmet UTKU Department of Geophysical Engineering, Faculty of of Bursa. The same authors state that the historic Engineering, Dokuz Eylül University, TR-35160, Buca-İzmir, Turkey earthquakes near İstanbul had magnitudes in the range 38 www.wjrr.org North Anatolian Fault Zone, Northern Turkey: Empirical Equations and the Changes in Some Kinematic Characteristics 6.8-7.2 (Ms) and occurred offshore and that the smaller by stress accumulation and creep. Bayrak et al. (2011) ones occurred in the east and west of the Marmara Sea. discussed the evaluation in the earthquake hazard In addition, they note that the seismicity for the last 500 parameters by dividing the North Anatolian Fault Zone years has been taking place with right-lateral into different segments. They used the method of Kijko displacement above 22 ± 3 mm/year, expected in the and Sellevoll (1989, 1992) in this study of theirs. Marmara Region. Gürbüz et al. (2000) indicate the Yucemen and Akkaya (2012) present a case study about seismic gaps concerning the 1754 earthquake with an the estimation of magnitude-frequency relationship using epicenter corresponding to the Gulf of İzmit and the 1766 the Modified Maximum Likelihood method. Le Pichon et earthquake with an epicenter corresponding to the central al. (2014) defined the geometry of the Southern Marmara Marmara basin, both with a magnitude of 7.5, in the Fault particularly on the basis of the exploration of seismotectonics of the Marmara Region that they seismic reflection profiles. Şengör et al. (2014) described discussed on the basis of the minor earthquakes they had the geometry of the North Anatolian Fault Zone in the recorded. Furthermore, they state that the distribution of Sea of Marmara in light of the multichannel seismic depths belonging to the seismicity in this area is reflection profiles in the Sea of Marmara. Scholz (2002), shallower than 15 km. Polat et al. (2002a,b) discuss the Shaw and Wesnousky (2008), Senatorski (2012), Shaw August 17, 1999 (Mw = 7.4) Gölcük (İzmit) earthquake in (2013) and Konstantinou (2014) dealt with the mechanics terms of the change in seismicity, its aftershocks, and the and kinematics of earthquakes and the faulting process. regional seismotectonics. In their study, the authors One of the recent studies was made by Yamamoto et al. emphasize that there had been no evident seismic activity (2015). In the study, they analyzed the data recorded by before the earthquake concerned. By quoting from Barka three ocean bottom seismographs (OBSs) over a period et al. (2000), Polat et al. (2002a) state that the surface of 3 months in 2014 to investigate the relationship of fault of the İzmit earthquake was above 150 km in the E- fault geometry to microseismicity under the western W direction and that the maximum displacement was Marmara Sea in Turkey. They showed that most of the measured as 5 m. In addition, they explain that the microearthquakes they identified occurred along the aftershocks were distributed in the upper section of the Marmara Fault (MMF). Their data indicate that the fault depth of the first 15 km and that 90% of them had depths plane of the MMF is almost vertical. They identified a between 5 and 15 km. They stress that the depth of the seismogenic zone that extends from 13 to 25 km depth main shock was 15 km. Utku (2003) investigated the through the upper and lower crust beneath the western macroseismic and instrumental observations for 29 Marmara Sea. earthquakes with magnitudes mb 4.8 that occurred in In this study, the seismic moment (M0)-magnitude the 1900-2002 period. In this study, they computed the (mb,Ms) and seismic moment-fault plane (A) relations stress drop as below 50 bars and intended to estimate the and the change in stress drop () that occurred along the seismic character of the zone concerned from the zone are examined according to the data about the behavior of the maximum annual magnitudes. earthquakes with mb,s 4.8 that occurred in the NAFZ in Accordingly, the behavior curve concerned reaches the the 1900-2000 process. mb and Ms denote body and maximum point 15 years after the minimum point on surface wave magnitudes, respectively. The study also average. The data period available for this evaluation encompasses the threshold magnitude value and the total based on data of almost 100 years is significant. Bayrak and mean displacement velocities for the visible fault and Öztürk (2004) discuss the time and spatial changes along the zone concerned.