Browsing by Author "Bekler, Feyza Nur."

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    Dynamic rupture process of the 1999 Düzce earthquake
    (Thesis (Ph.D.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2018., 2018.) Bekler, Feyza Nur.; Konca, Ali Özgün.; Özel, Nurcan Meral.
    Rupture process of large magnitude earthquakes have been generally performed by using a kinematic approach. A typical set of input parameters for kinematic approach includes; fault length, fault depth, rupture velocity, slip distribution and rise time defining the slip velocity time function. Kinematic models have been quite successful in obtaining detailed slip distribution maps of large earthquakes. However, the kinematic models have their own disadvantages. One major disadvantage is that the physics of the kinematic inversion scheme is incomplete. One uses representation theorem and Green’s functions approach to obtain slip distribution without considering the forces and the frictional properties on the fault interface. In fact, it is not clear whether the kinematic models of earthquakes with the inverted slip and rise time distributions are physical plausible. This lack of physical constraint on physical properties and the force balance leads to lack of long-term behavioral property of the fault. Dynamic modeling has been proposed as a new perspective to explain complexity of source parameters, rupture radiation pattern and slip distribution. One way of understanding the dynamic and kinematic mechanism of the earthquake source is to model how the rupture process improves. Hence, proper understanding of this process and appropriate modeling approaches play an important role in seismic hazard and seismic mitigation estimations. On the other hand, the modeling of a dynamic rupture process of an earthquake may provide information on how the limitations on the source can be understood.
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    Search of optimal crustal velocities using waveform modelling of local earthquakes
    (Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2005., 2004.) Bekler, Feyza Nur.; Aktar, Mustafa.
    One of the concerns of geophysicist during the last decade is to reduce the damage of earthquakes. As a result, seismic hazard studies have become an integral part of long term planning and mitigation. One approach is to calculate pe.ak ground acceleration (PGA) and use this scalar value in building design. However, this method has some disadvantages: it is very simple and it does not give spectral information related to the ground motion. Generally, the effects of faulting type, source mechanism, rupture directivity, asperities are ignored during the calculation of the PGA values. The study in this thesis contributes to the simulation of the ground motion by constructing optimal crustal velocity models based on 1- D synthetic seismogram modeling. For this purpose, different crustal models were generated using the discrete wave-number technique (Bouchon, 1981) and they have been tested by searching the best-fit between observed and synthetic seismograms. Waveforms from 5 earthquakes were analyzed in this study. The selected earthquakes have magnitudes larger than 3.5 and they are located along the main fault zone in the Sea of Marmara. The vertical, radial and transversal components were compared using the cross correlation coefficient between observed and synthetic seismograms. Crustal models having S-layers with fixed depths were used to calculate the synthetics for each selected event. First, the optimum P-wave velocities were searched within predefined velocity limits for each layer. Once the optimum P velocities were obtained, then the S wave velocities have been searched. In general a moderate level of fitting is obtained even for the optimal crustal models. Although numerically the correlation values are quite low, the shapes of the waveforms are roughly close to each other, at least for some selected parts of the total waveform. The degree of fitting is particularly low in the part of the waveform where the 3-dimentional effects in the crust start to dominate, such as the P-arrivals in the transversal component. The performance also degrades with the level of the local noise, which is known to be not negligeable at ISKB station. The use of a clever search algorithm that uses a feedback mechanism to guide the search in a selective parameter space and accelerates the convergence towards the optimum (such as steepest descent, etc) will allow the scanning of wider range of parameter (eg estimating the layer depths in parallel to velocities, etc). This will certainely improve the results.