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    Application of GPR to normal faults in the Buyuk Menderes Graben, western Turkey
    (Pergamon-Elsevier Science Ltd, 2013) Yalciner, Cahit Caglar; Altunel, Erhan; Bano, Maksim; Meghraoui, Mustapha; Karabacak, Volkan; Akyuz, H. Serdar
    Paleoseismology documents past surface-rupturing earthquakes that occurred on faults. This study is limited by the scarcity data on geomorphic and sedimentary environments that may preserve adequate records of deposition, erosion, and fault slip markers. Identifying relevant trenching sites can be difficult when a fault is buried or its surface expression has been eroded since the last tectonic motion. Ground penetrating radar (GPR) is an effective tool for locating suitable sites for trenching. Characteristic reflections are produced by boundaries between elements with contrasting electrical properties, such as grain size distribution (sorting, clay content, etc.), porosity, and water content. GPR is capable of resolving faults by imaging offset stratigraphic reflectors or reflections from the fault plane. GPR surveys were performed at two sites along the Buyuk Menderes Graben (western Turkey) to precisely locate the normal fault zone; there is no clear evidence of surface rupture at these sites. We used 250 and 500 MHz antennas for receiving the GPR data. From the GPR measurements, we determined locations suitable for paleoseismic investigations and performed a trenching study across the fault plane. The comparison of the GPR results and the trenching study indicates a good correlation between these methods. (C) 2012 Elsevier Ltd. All rights reserved.
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    Paleoseismic history and slip rate along the Sapanca-Akyazi segment of the 1999 Izmit earthquake rupture (Mw=7.4) of the North Anatolian Fault (Turkey)
    (Elsevier Science Bv, 2018) Dikbas, Aynur; Akyuz, H. Serdar; Meghraoui, Mustapha; Ferry, Matthieu; Altunel, Erhan; Zabci, Cengiz; Langridge, Robert
    The Sapanca-Alcyazi segment (SAS) is located on western part of the North Anatolian Fault (NAF) of Turkey. It was ruptured together with four other segments during the 17th August 1999 Izmit earthquake (M-w = 7.4) which caused similar to 145-km-long surface rupture in the east Marmara region. We conducted geomorphological investigations and 2D-3D paleoseismic trenching at 3 different sites near the Sakarya River along the SAS to obtain new data for the timing of past earthquakes and slip rate of this section of the NAF. Detailed investigations using Ground Penetrating Radar on the western bank of the Sakarya River reveal 18.5 +/- 0.5 m of right-lateral cumulative offset of an alluvial terrace dated as 850 +/- 11 years BP using Optically Stimulated Luminescence. The analysis of trench data from the three different sites of the SAS indicates the occurrence of four surface rupturing past earthquakes including the 1999 Izmit earthquake. According to the radiocarbon dating, these paleo-earthquakes can be correlated with the 1719 CE, 1567 CE, and 1037 CE historical earthquakes and suggest an average recurrence period between 273 and 322 years. The total dextral offset, the age of trench units and the terrace deposits together suggest a 22 +/- 3 mm/yr slip rate for this portion of the NAF.
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    Subaqueous fault scarps of the North Anatolian Fault in the Gulf of Saros (NE Aegean); where is the western limit of the 1912 Murefte-Sarkoy earthquake rupture?
    (Oxford Univ Press, 2022) Aksoy, M. Ersen; Meghraoui, Mustapha; Polonia, Alina; Cagatay, M. Namik; Yavuzoglu, Asli Zeynep; Onder, Sebnem; Ulgen, Umut B.
    The westernmost segment of the North Anatolian fault in NW Turkey lies mostly offshore, in the Sea of Marmara and the Gulf of Saros (NE Aegean), respectively to the E and W of a 45 km inland central portion. The 9 August 1912 Murefte-Sarkoy (M-s 7.4) and 13 September 1912 (M-s 6.8) earthquakes occurred along this segment. To date, the segment was studied mostly onshore although estimated magnitude and location suggest an offshore extension. Recent studies show the eastern rupture extension in the Sea of Marmara, while its western counterpart in the Gulf of Saros remains less documented. Here we use new observations from high-resolution marine geophysical data (multibeam bathymetry, side-scan-sonar, and seismic reflection profiles), to constrain the offshore 1912 ruptures in the Gulf of Saros. Detailed mapping of the subaqueous fine-scale morphology and structure of the fault provides a new insight for the western limit of the two 1912 surface ruptures. Distribution of fresh scarps, 3-D structural reconstructions, the complexity of fault segments, and the recent seismicity, altogether suggest that the western termination of the 1912 rupture(s) ends 37 km offshore in the Gulf of Saros. Following the 1999 Kocaeli earthquake, in the eastern Sea of Marmara, the unruptured segment length between the 1999 and 1912 ruptures became a critical issue, because of its implication for future earthquakes in the so-called Marmara seismic gap. If a 150-160 km total rupture length for the two 1912 earthquakes is assumed, a western rupture termination point at the inner Saros basin margin means that the eastern extension of the 9 August earthquake rupture reached the Central Marmara Basin. This outcome necessarily has implications for the seismic hazard in the Marmara coastal area that includes the Istanbul metropolitan area.