Seismic hazard analysis of Yedisu fault (North Anatolian Fault)

Seismic hazard analysis of Yedisu Fault between Üzümlü town of Erzincan and Yedisu town of Bingöl in the eastern part of the North Anatolian Fault (NAF) and approximately located in N70W was generated. In general, the geology of throughout and around the segment of Yedisu has been composed of rock types such as the ophiolitic melange formed by the closure of the Neotethyan Ocean, deep-sea pelagic sediments, pyroclastic rocks, flysch, limestone, marl, agglomerate, volcanic breccia, basalt, and andesite. Alluvion, alluvial fan and talus are in the middle of the basins and riverbeds. These area is called soft soil resulting from these units not harden. Turkey is the youngest and most active part of the Alpine orogenic system. Alpine orogenic system created by the closure of the different arms of the Tethys Ocean. During the closing of the Tethys Ocean, Gondwana and belong to different crustal fragments Lavrasya collide and merge into each other. Turkey is a collage composed of remains of this orogenic crustal fragments and fused them separating oceanic environment. Because of continent-continent collision depending on the Bitlis Suture closure of the Neo-Tethys during the middle Miocene, the neotectionic period starts. Turkey constitutes the more developed western part of asymmetric tectonic escape system due to after the convergence and collision of the Arabian Platform in Asia. The Arabian Peninsula has continued to move north along the Dead Sea and has created a compression tectonic regime at the East Anatolia. This compressional regime between 11 and 5 Ma has led to the rise of Eastern Anatolia and crustal thickening. During this time, the east-west trending reverse faults, thrusts, folds and some ramp basins are developed. Before the beginning of the Pliocene about 5 Ma, the location of this compressional regime has taken the escape regime. Anatolian plate began to move westward along the two-transform faults: North Anatolian Fault Zone (NAFZ) and East Anatolian Fault Zone (EAFZ). NAFZ is one of the most active of the major lateral faults on the world. NAFZ that approximately 1.200 km in length forms the northern boundary of the Anatolian Block. NAFZ is starting from the trible junctions Karlıova in the east, follows approximately 100 km south of the Black Sea cost line, and extends to the north of the Aegean Sea, the Gulf of Saros. It colligates high plateau of Anatolia and Aegean Taphrogen. NAFZ has formed by the beginning of neotectionic in Turkey. Many destructive earthquakes along the NAFZ have occurred during the escape regime. While analyzing the records of the instrumental period of earthquakes in Turkey, thoughout the NAFZ has observed that Marmara Sea section and the segment of Yedisu, called seismic gaps, are not broken into the earthquake serie formed in the 1900. Yedisu segment have examined with paleosismological studies. Sarıkaya Trench, the depth of 2.5 m, has opened at the western part of the segment and Tokmanik Trench, a depth of about 4 m, has opened at the eastern part of the segment near to Yedisu Basin. Samples taken from these trenches were dated by 14C test and the results indicate earthquakes located in the historical earthquake catalog. 1784 earthquake, the most recent earthquake occurred on this segment, was observed in both trenches. In the light of the paleoseismological research on this segment, the earthquake recurrence period is determined as 245±55 years. The factors that the segment is unbroken during the earthquake series, any earthquake is recorded over the last 231 years, and NAF moves an annual average of 2 cm are clearly indicated that the breakage of this segment is very high. All these factors and earthquakes that occurred before the fault to the east and west are increased the accumulated energy on the segment. In case of the breaking the Yedisu Segment, a seismic hazard analysis has generated to make the model of seismic felt intensity at troughout and aroun the segment. Seismic hazard analysis is divided into two types: deterministic and probabilistic. The deterministic seismic hazard analysis has been used within the scope of this thesis. Determination of the earthquake source or sources, finding the shortest distance between residantial or study area with the source, the calculation of ground motion parameters (such as PGA, PGV) depending on this distance, and displaying the graphical of the changing PGA values based on distance constitute the necessary conditions for this analysis. Using ArcGIS that one of the geographic information system software program, the geology map of the study area has been updated in company with satellite images and MTA geology maps. Each formation has been drawn containing the information about age, lithology, shear velocity (VS30) values and the coefficient based on these values used in attenuation relationships. The location and the length of the segment is mapped by the current active fault map. Thus, the average lentght of the segment is determined as 72 km. The moment magnitude is determined as 7.2 using the empirical equation of Wells and Coppersmith (1994) which provides to define the earthquake magnitude with regard to the length of the fault. The soil types are divided into three based on VS30 values which argued by Kalkan and Gülkan (2004). Accordingly, the areas of Late Pleistocene – Holocene aged alluvium and alluvial fan has given 200 m/sec where the shear velocity value of soft soil. The group of agglomerate, sandstone and claystone that Early Miocene – Early Pliocene aged have given 400 m /sec the shear velocity value of stiff soil. The group of Pliocene – Quaternary aged lava rocks and meta-clastic, meta-dunite, meta-serpantine, ophiolitic melange, volcanic breccia and reef limestone that their age is older than Miocene has given 700 m/sec the shear velocity value of rock. To calculate the value of peak ground accelaration of the amplitude parameter that the characteristic features of the strong ground motion, many attenuation relationships were researched and some of them is implemented to study area. While some of these relationships give erroneous results according to the soil types, the others give very high results. Therefore, the near source attenuation relationship belonging to Kalkan ve Gülkan (2004) is given convenient results for the study area. The study area has been divided into 121.424 points by the agency of used program and each point has the information of their formation. After the necessary calculation for the attenuation relationships, now a peak ground acceleration (PGA) values for each of these points was assigned. To obtain the felt intensity from the PGA values, the empircal equations of Arıoğlu et al. (2001) and Bilal and Askan (2014) have been used. The equation of Arıoğlu et al. (2001) for the attenuation relationship gave the values of the felt intensity as 7, 8, 9, and 10, respectively. The equaiton of Bilal and Askan (2014) for te attenuation relationship gave the values of the felt intensity as 8, 9, 10, and 11, respectively. The equation of Bilal and Askan (2014) gives a more reliable result than Arıoğlu et al. (2001) beacuse the equation was generated more seismic data than the other equation.