Browsing by Author "Korkusuz, Yasemin."

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    Dynamic earthquake rupture simulations in the sea of Marmara
    (Thesis (Ph.D.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2019., 2019.) Korkusuz, Yasemin.; Konca, Ali Özgün.; Özel, Nurcan Meral.
    The 1912 Mürefte and 1999 Izmit M"7.4 earthquakes are the last devastating events of the western and eastern sections of the Marmara region, respectively. The center of the Sea of Marmara, the region between locations of these two earthquakes, is prone to creating another large earthquake. The main objective of our study is to determine 3D dynamic earthquake rupture scenarios, considering non-planar and heterogeneous stress distribution in the Sea of Marmara. Recent studies show that some segments of the North Anatolian Fault (NAF) beneath Marmara are partially creeping. In this study, it is the first time that we attempt to generate realistic earthquake scenarios by putting constrains on initial stress on the fault using regional stress from earthquake focal mechanisms, in addition to stress release during past earthquakes and strain accumulation during interseismic period using geodetical measurements on slip-rate and locking depth at various segments along the NAF beneath the Sea of Marmara. In order to constrain the regional stress in addition to our previous five cluster analysis a new earthquake cluster is analyzed in the Central Marmara Basin. We use 3D Finite Element Method (PyLith) for dynamic earthquake simulations and tetragonal mesh for better smoothing at the fault bends, which allows us to implement nonplanar fault geometry and initial stress heterogeneity using slip-weakening friction law. We place constraints on initial shear stress from geodetic and seismic studies of locking depth and interseismic strain accumulation. We consider 80 rupture scenarios and calculate slip distribution, rupture velocity and moment magnitude in addition to slip-rate and traction on the fault surface, and displacement and velocity on the ground surface. We find that for the most scenarios possible earthquake magnitude does not exceed Mw7.2. In addition, in none of the possible scenarios we obtain super-shear rupture velocity. We find that depending on the location of the initiation point, asperities in the partially creeping segments and loaded initial stress, the rupture may not extend into the Prince’s Island Segment.
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    The present day stress states in the Marmara region
    (Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2012., 2012.) Korkusuz, Yasemin.; Özel, Nurcan Meral.
    Stress tensors with the aid of a large number of fault plane solutions provide important contributions for the evaluation of the seismotectonic setting of a region. In this study, recent earthquake activity at Ganos offshore, Tekirdağ Basin, Çınarcık Basin, Yalova Region and Gemlik Region, which are all located on the western branches of the North Anatolian Fault Zone, were analyzed using a current data set of fault plane solutions derived from a very dense seismic network. For the analysis of high quality fault plane solutions, data from KOERI and the TURDEP project was merged. Data from a total of 105 stations, including 5 continuous SBO stations of KOERI was used. The earthquakes were selected with the following criteria; minimum local magnitude of 2.0, number of minimum P-wave first motion polarity of 10 and toleration of maximum misfit of 1. During the study 85, 75, 73, 102, and 63 source mechanisms were determined in Ganos Offshore, Tekirdağ Basin, Çınarcık Basin, Yalova Region and Gemlik Region, respectively. Through the determination of 9226 high quality P-wave first motion polarities for the selected 398 earthquakes, the number of average polarity per earthquake was 23. Average error depth, latitude, longitude, and GAP values were also obtained as 2.75 km, 0.98 km, 1.25 km and 63˚, respectively. Furthermore, using the algorithm of Horiuchi et al., (1995), simultaneous focal mechanism solutions of individual earthquakes and recent stress regimes along with R-values have been determined for the five clusters. As a result, it was found out that NW-SE trending trans-tensional stress structures leading mostly normal and oblique faulting systems are predominant in Tekirdağ Basin, Çınarcık Basin, Yalova and Gemlik clusters. Nevertheless, Ganos Cluster was presented as a dextral strike-slip deformation system through the transition from normal to reverse faulting system. Vertically oriented Sigma-2 axis was obtained for the Ganos Offshore cluster, whereas in all other regions Sigma-1 axis was vertical. Furthermore, data from KOERI and the TURDEP project was also merged in order to analyze 25.07.2011 Marmara Sea and 16.08.2011 Gemlik Gulf Earthquakes with local magnitudes of 5.2 and 4.0, respectively. It was stated that the stress tensor solutions obtained using mostly small size earthquakes fit the source mechanisms of these two moderate size earthquakes. Consequently, in this research, I have proposed a new and comprehensive approach to the fault geometries, present stress state, and seismotectonic structures of the Marmara Region by a detailed analysis of the results of the large number of fault plane solutions of earthquakes in the Marmara Region using the most dense seismic network of Turkey.