Ph.D. Theses
Permanent URI for this collection
Browse
Browsing Ph.D. Theses by Subject "Earthquakes -- Turkey."
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Determination of upper mantle heterogeneity beneath Aegean-Anatolian region from travel time tomography(Thesis (Ph.D.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2019., 2019.) Aksarı, Doğan.; Karabulut, Hayrullah.The objective of this work is to determine the heterogeneities of the upper mantle in the Aegean-Anatolian domain using teleseismic tomography. A waveform dataset was prepared from 798 teleseismic earthquakes with magnitudes greater than 5.5 between January 2004 and December 2015. 417 stations from permanent and temporary networks with more than 64,000 direct P phases are used in the computations. The relative travel times of P waves with respect to the ak135 (Kennett et al. 1995) earth model are computed using waveform cross-correlations technique. The tomographic images are computed as perturbations with respect to ak135 earth model. An algorithm named as fast marching method (FMM) (Sethian, 1996a, 1996b) based on the solution of Eikonal equation is used in the forward computation of the travel times. The inversion is performed using subspace inversion scheme. Trade-off curves are plotted and several synthetic tests are performed in order to select optimum parameters (damping and smoothing) for tomography and the resolution and model roughness were investigated. The tomographic images obtained to a depth of 700 km. The computed tomographic images show a heterogeneous upper mantle structure in the Aegean-Anatolian domain. The results are similar to the previously published images mostly but provides higher resolution for the study area. Both Hellenic and Cyprus subductions are imaged to the depth of 700 km. The tear (Pliny-Strabo Tear) between two subduction zones is clearly observed reaching to 660 km discontinuity. A smaller scale tear (Antalya Bay Tear) is also observed on the Cyprus slab around Paphos Transform Fault. The Anatolian plate is underlined by low velocity mantle material with thickness increasing from west to east. The northern block of the North Anatolian Fault (NAF) is observed as high velocity body observable to a depth of 100-200 km. NAF has a sharp velocity contrast between the north and south.Item Paleoseismological studies on Düzce fault and geological data on the seismogenic sources in the vicinity of Düzce area(Thesis (Ph.D.)- Bogazici University. Kandilli Observatory and Eartquake Research Institute, 2005., 2005.) Komut, Tolga.; Gürbüz, Cemil.In 1999, two earthquakes ruptured the Northern Almaclk strand (NAIS) of the North Anatolian Fault that includes the Diizce and Aksu faults, producing surface rupture along the northern border of the Almaclk block. Paleoseismological trenching is performed at four sites along the Aydmpmar and Mengencik segments of four-structural-segmented Diizce fault. Six dated-events from eleven trenches that cross cuts the fault zone provided insights on its seismogenic behavior. The excavations from five trenches at three sites expose evidence for six earthquakes that occurred since B. C. 1740. A shallow of watertable, unfavorable trench materials and lack of financial support to perform 3-D trenching made the identification anu characterization of individual paleoearthquakes difficult. However, by integrating date constrains of events from the trenches that were performed along the Diizce fault including previous studies along the easternmost segment, a periodical recurrence model seems to be concordant with the radiocarbon age data. Seven serial surface-rupturing earthquakes including the 1999 Diizce event along the Diizce fault are defined. The model suggests that the Diizce fault is behaving as a single seismic segment at least for the last serial rupture in Holocene time. The additional two older events are showing an irregularity in the serial. Hitherto unrecognized earthquakes probably would eliminate this irregularity. A recurrence interval is estimated by also considering the two older earthquakes. This final sequential model suggests that 1999-type earthquakes repeat each 355±35 year (% 70 probability). The slip rate that was calculated from 350 cm average slir of the 1999 event and the recurrence period is about 9.5±1 mmlyr having % 70 probability. This value is in agreement with geodetic measurements (10 mmlyr) from independent studies. Because short time has elapsed since the 1999 earthquake that occurred along the Diizce fault, the Diizce fault does not appear to have an important seismogenic potential in near future. The Diizce plain is one of the major basins of the Marmara region. There is no active faulting excluding Diizce and Aksu faults that is detected in the basin and surrounding borders according to this study. In addition to this pull-apart and then continuing active formation of the Diizce basin hypothesis is not validated by rigorous data. Therefore, considering these data, it may be suggested that Diizce area is not under a severe seismogenic threat for very near future.Item Studying seismotectonics of Eastern and Southern Anatolia using earthquake mechanisms(Thesis (Ph.D.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2019., 2019.) Güvercin, Sezim Ezgi.; Konca, Ali Özgün.The Anatolia-Aegean domain provides a unique opportunity to explore plate interactions where oceanic subduction, continental collision and transform plate motions are observed simultaneously. High seismicity rates and diversity of the earthquake source mechanisms are the result of the accommodation of these relative plate motions. As the initial tectonic buildup involves the amalgamation of different tectonic units, it is natural that lithospheric segments with varying structural properties in this relatively small region also contributes to the complexities of the observations. Understanding interactions of these plates and related deformation requires an integrated analysis of various observations such as seismic tomography, earthquake slip models, geodetic observations and stress changes along with the seismicity and earthquake source mechanisms. In this thesis, 3 case studies in different tectonic settings are presented: the continental collision in the east, the extension due to roll back in the west and the transition between extension and compression. For these 3 case studies, the relation of earthquake source mechanisms to other seismological and geodetic data is used to better understand the present state of the seismotectonics of Easternmost Mediterranean including eastern Anatolia. The October 23, 2011 Mw7.1 Van, Eastern Anatolia earthquake which is on an EW trending thrust fault, in a region under N-S compression due to the convergence of the Arabian plate toward Eurasia. The three faults were activated during and after the coseismic rupture. The earthquake source mechanisms with consistent orientations are grouped in three clusters. An average fault mechanism is calculated for each cluster by the summation of moment tensors. The triggered faults have experienced Coulomb stress increase due to co-seismic rupture revealing a mechanism which accommodates NS shortening in the region. The June 20, 2017 Mw 6.6 Bodrum-Kos earthquake which occurred on an E-W trending normal fault is related to the roll back effect of Hellenic Subduction. The Bodrum-Kos event revealed that the extension in the western section of Gökova Bay is accommodated by a north dipping fault. Two different fault slip models, dipping to north and south, are used to compute the Coulomb stress changes at different depths. The coherency between the seismicity and the regions of increased stress is used to put a constraint on the dip of the ruptured fault. The gradual change of strikes of aftershock mechanisms from east to west is consistent with the rotation of the strain field region indicating that the observed earthquake pattern during the 2017 earthquake reflects the long term tectonic frame work in the region. In between these compressive tectonics of Eastern Anatolia and extension in the Aegean, Cyprus Arc region acts as a transitional zone which is tectonically less understood. Specifically how the convergence of Nubia toward Anatolia is accommodated remains unclear. By the analyses of novel earthquake source mechanisms, and other seismological and geodetic data, it is proposed that the segmentation of the subducting Nubian Plate has a significant contribution to the lithospheric deformation. The change in the orientations of the earthquake mechanisms around the Isparta Angle determines the eastern boundary of the N-S extension due to roll back of the Hellenic slab and is consistent with the counter clockwise rotation of AnatoliaAegean domain which is revealed by the recent GPS vector field. Thrust mechanism earthquakes along with Bouguer gravity, seismicity, and horizontal GPS velocities reveal the geometry of the subducting slab beneath Antalya Basin towards N-E. We suggest that the Antalya Slab deforms as an isolated block, responding in part to adjacent plates, including the Anatolian Plate that moves toward the west, overriding the remnant Antalya slab.