Paleoseismology of the North Anatolian Fault at Güzelköy (Ganos segment, Turkey): Size and recurrence time of earthquake ruptures west of the Sea of Marmara Mustapha Meghraoui, M. Ersen Aksoy, H Serdar Akyüz, Matthieu Ferry, Aynur Dikbaş, Erhan Altunel To cite this version: Mustapha Meghraoui, M. Ersen Aksoy, H Serdar Akyüz, Matthieu Ferry, Aynur Dikbaş, et al.. Pale- oseismology of the North Anatolian Fault at Güzelköy (Ganos segment, Turkey): Size and recurrence time of earthquake ruptures west of the Sea of Marmara. Geochemistry, Geophysics, Geosystems, AGU and the Geochemical Society, 2012, 10.1029/2011GC003960. hal-01264190 HAL Id: hal-01264190 https://hal.archives-ouvertes.fr/hal-01264190 Submitted on 1 Feb 2016 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Article Volume 13, Number 4 12 April 2012 Q04005, doi:10.1029/2011GC003960 ISSN: 1525-2027 Paleoseismology of the North Anatolian Fault at Güzelköy (Ganos segment, Turkey): Size and recurrence time of earthquake ruptures west of the Sea of Marmara Mustapha Meghraoui Institut de Physique du Globe de Strasbourg (UMR 7516), F-67084 Strasbourg, France ([email protected]) M. Ersen Aksoy Institut de Physique du Globe de Strasbourg (UMR 7516), F-67084 Strasbourg, France Eurasia Institute of Earth Sciences, Istanbul Technical University, 34469 Istanbul, Turkey Now at Instituto Dom Luiz, Universidade de Lisboa, P-1750-129 Lisbon, Portugal H. Serdar Akyüz Department of Geology, Faculty of Mines, Istanbul Technical University, Maslak, 34469 Istanbul, Turkey Matthieu Ferry Institut de Physique du Globe de Strasbourg (UMR 7516), F-67084 Strasbourg, France Now at Geosciences Montpellier, F-34095 Montpellier, France Aynur Dikbaş Eurasia Institute of Earth Sciences, Istanbul Technical University, 34469 Istanbul, Turkey Department of Geology, Faculty of Mines, Istanbul Technical University, Maslak, 34469 Istanbul, Turkey Erhan Altunel Department of Geology, Eskişehir Osmangazi University, 26480 Eskişehir, Turkey [1] The Ganos fault is the westernmost segment of the North Anatolian Fault that experienced the Mw = 7.4 earthquake of 9 August 1912. The earthquake revealed 45-km-long of surface ruptures inland, trending N70E, and 5.5 m of maximum right lateral offset near Güzelköy. The long-term deformation of the fault is clearly expressed by several pull-apart basins and sag ponds, pressure and shutter ridges and offset streams. In parallel with detailed geomorphologic investigations, we measured co-seismic and cumulative displacements along the fault, and selected the Güzelköy site for paleoseismology. A microtopographic survey at the site yields 10.5 Æ 0.5 m and 35.4 Æ 1.5 m cumulative lateral offsets of stream channels and geomorphologic features. Seven paleoseismic parallel and cross-fault trenches document successive faulting events and provide the timing of past earthquakes on the Ganos fault segment. Radiocarbon dating of successive colluvial wedges in trench T1, and the fresh scarplet above (probably 1912 surface rupture) Copyright 2012 by the American Geophysical Union 1 of 26 Geochemistry Geophysics 3 MEGHRAOUI ET AL.: PALEOSEISMOLOGY OF NAF (GANOS, TURKEY) 10.1029/2011GC003960 Geosystems G indicate the occurrence of three faulting events since the 14th century. Parallel trenches (3, 5, 6 and 7) expose paleo-channels and show a cumulative right-lateral offset of 16.5 Æ 1.5 m next to the fault, and 21.3 Æ 1.5 m total channel deflection. Radiocarbon dating of past channel units and fault scarp-related colluvial deposits imply an average 17 +/À 5 mm/year slip rate and 323 Æ 142 years recurrence interval of large earthquakes during the last 1000 years on the Ganos fault. The succession of past faulting events and inferred slip rate west of the Marmara Sea provide more constraint on the long-term faulting behavior in the seismic gap of the North Anatolian Fault and may contribute to a better seismic hazard assessment in the Istanbul region. Components: 14,800 words, 14 figures, 5 tables. Keywords: 1912 Mürefte earthquake; Ganos fault segment; Marmara; North Anatolian Fault; paleoseismology. Index Terms: 7221 Seismology: Paleoseismology (8036); 7230 Seismology: Seismicity and tectonics (1207, 1217, 1240, 1242); 8111 Tectonophysics: Continental tectonics: strike-slip and transform. Received 14 November 2011; Revised 29 February 2012; Accepted 1 March 2012; Published 12 April 2012. Meghraoui, M., M. E. Aksoy, H. S. Akyüz, M. Ferry, A. Dikbaş, and E. Altunel (2012), Paleoseismology of the North Anatolian Fault at Güzelköy (Ganos segment, Turkey): Size and recurrence time of earthquake ruptures west of the Sea of Marmara, Geochem. Geophys. Geosyst., 13, Q04005, doi:10.1029/2011GC003960. 1. Introduction same fault branch. Hence, the consistent repeti- tion of co-seismic movements on the same fault [2] The record of past earthquakes in superficial rupture offers the possibility to identify the trace geological units is a key element in paleoseismolo- of paleoearthquakes. The paleoseismology of the gical investigations. As generally observed in tren- Ganos fault may therefore provide some constraints ches, the repeated surface faulting with significant on the timing of past earthquakes and slip rate on co-seismic slip characterizes the size and recurrence the NAF immediately west of the Sea of Marmara. time of past seismic events. The 9 August 1912 [3] Paleoseismology includes various field tech- Mürefte earthquake (Ms = 7.3 [Ambraseys, 2002]) niques that involve crosscutting and parallel tren- occurred along the western section of the North ching and isotopic dating of sedimentary units Anatolian Fault (NAF) and displayed surface fault- aided with topographic surveys and sometimes ing along the 45-km-long inland section of the shallow geophysics [McCalpin, 2009]. The size Ganos segment (Figures 1 and 2). The earthquake and characteristics of past earthquake ruptures caused human loss and severe damage in a wide are accessible through detailed field studies along area and affected cities such as Şarköy, Mürefte and the North Anatolian Fault [Rockwell et al., 2001; Gaziköy in the epicentral area [Ambraseys and Klinger et al., 2003; Ferry et al., 2004; Hartleb Finkel, 1987; Sadi, 1912; Mihailovic, 1927]. Co- et al., 2006; Palyvos et al., 2007; Pantosti et al., seismic surface rupture and slip, showing up to 2008; Rockwell et al., 2009; Fraser et al., 2010; 5.5 m right-lateral offsets, were described in con- Kondo et al., 2010; Zabcı et al., 2011; Dikbaş and temporaneous reports and more recent studies Akyüz, 2011]. Previous paleoseismic investigations (Figure 2) [Mihailovic, 1927; Altunel et al., 2004; along the Ganos fault segment focused near the Aksoy et al., 2010]. According to photographs taken Saros Bay at the westernmost section of the 1912 soon after the main shock [Mihailovic, 1927], the rupture, and determined four surface ruptures during surface breaks exhibited linear fault scarps, mole the past 1100 years [Rockwell et al., 2001]. More tracks and en-echelon ruptures similar to those recent trenching studies at the Saros Bay con- observed during the 17 August 1999 İzmit earth- strained four surface faulting after AD 900 and quake (Mw 7.4 [Barka et al., 2002]). The geomor- displayed a 9 Æ 1 m channel offset related to the last phology along the fault strike shows that in several two events [Rockwell et al., 2009]. Paleoearth- locations, the 1912 co-seismic offset coincides with quakes of the Saros Bay region are likely to corre- cumulative offset observed on streams, ridges and spond to the 1063 and 1343 or 1354, 1659 or 1766 old path deflections. This coincidence indicates and 1912 historical seismic events [Rockwell et al., a localized coseismic surface deformation on the 2009; Aksoy, 2009]. 2of26 Geochemistry Geophysics 3 MEGHRAOUI ET AL.: PALEOSEISMOLOGY OF NAF (GANOS, TURKEY) 10.1029/2011GC003960 Geosystems G Figure 1. The North Anatolian Fault (NAF, red and black lines) in the Marmara Sea and neighboring regions. The Ganos fault segment is the site of the 9 August 1912 earthquake (Mw 7.4 [Aksoy et al., 2010]) and represents the west- ernmost fault segment of the NAF (red line for northern branch, and black line for southern branch). Yellow boxes are historical earthquakes [Ambraseys, 2002], and the simplified fault zone in the Marmara Sea bottom is according to Armijo et al. [2005]. The inset shows the 1939–1999 earthquake sequence and geodetic rate along the NAF and the loca- tion of the 1912 out of sequence earthquake segment [Barka, 1996; Hubert-Ferrari et al., 2000; Reilinger et al., 2006]. [4] The study of rupture dimension using the 1912 Marmara seismic gap [Aksoy, 2009; Aksoy et al., co-seismic slip distribution, fault geometry and the 2010]. As the total 1912 co-seismic rupture length analysis of seismic records suggests a total length supersedes the 45-km-long inland Ganos fault, a of 140 Æ 20 km for the 1912 Mw 7.4 rupture significant fault section is located offshore. Off- which determines the western limit of the Sea of shore investigations of the fault rupture were Figure 2. (a) The Ganos fault inland (red line) and 1912 right-lateral coseismic slip in boxes [Aksoy et al., 2010]. The star represents the 1912 epicenter location according to Ambraseys [2002]. The Güzelköy paleoseismic site is in the NE section of the fault. (b) The paleoseismic site is in box on the 1912 fault (red line) with slip distribution (numbers) indicating a zone maximum right-lateral slip (maximum 5.5 m in red [Aksoy, 2009]). 3of26 Geochemistry Geophysics 3 MEGHRAOUI ET AL.: PALEOSEISMOLOGY OF NAF (GANOS, TURKEY) 10.1029/2011GC003960 Geosystems G Table 1.