Sedimentary record of coseismic subsidence in Hersek coastal lagoon (Izmit Bay, Turkey) and the late Holocene activity of the North Anatolian Fault
Sébastien BertrandLisa A. DonerSena Akçer ÖnÜmmühan SancarUlla SchudackSteffen MischkeM. Namık ÇağataySuzanne A.G. Leroy
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Abstract:
The late Holocene activity of a restraining bend of the northern strand of the North Anatolian Fault in Izmit Bay was investigated by a sedimentological, geochemical, and paleoecological analysis of sediment cores from Hersek coastal lagoon, NW Turkey. The sediment cores show a succession of sedimentary sequences composed of three units separated by gradual transitions. The first unit is composed of a thin layer of shell debris-rich sediment in abrupt contact with the underlying organic-rich deposits. This unit is overlain by a thick foraminifera-rich mud deposit, and the sequences are capped by an organic-rich mud unit. These sequences are interpreted as silting up, shallowing upward deposits, typical of a lagoon becoming isolated from the sea. We suggest that they represent the sedimentary signature of coseismic subsidence, which was caused by reverse slip at the Hersek bend, and tsunamis in Izmit Bay. Our radiocarbon-dated paleoseismological record indicates (1) the atypical collapse of the hanging wall during the 740 earthquake and (2) subsidence of the footwall during the 987, 1509, and 1719 earthquakes. This study contributes to the understanding of the dynamics of restraining bends, and it highlights the potential of coastal sediments for reconstructing past earthquakes and tsunamis in regions dominated by strike-slip deformations.Keywords:
North Anatolian Fault
Paleoseismology
The North Anatolian Fault (NAF), located in Turkey, is one of the world's most active faults and accommodates Anatolia's westward motion relative to Eurasia. Over the last century, several earthquakes (M>6.8) have migrated from east to west. It is in the Marmara region, south of Istanbul, that the subsequent rupture is expected. However, this is where the geometry of the fault becomes more complex. It divides into three branches, one of which borders Lake Iznik and the southern Marmara Sea. As there is now very little seismic activity along this portion of the NAF (MNAF), and GPS only detects small displacements (Reilinger et al., 2006), it is thought to be inactive. However, the city of Iznik, the cradle of Christianity, has preserved valuable historical evidence in contrast to its observations. Therefore, to better understand the seismic hazard in this area, it is necessary to catalogue the seismic activity and locate past ruptures.Two active faults were discovered in Lake Iznik thanks to our geophysical and coring campaigns (Gastineau et al., 2021). The study of short (<4m) sediment cores sampled on both sides of the E-W fault running close to Iznik city reveals that the previous rupture (1065 CE) coincides with a highly destructive historical earthquake recorded in the city's archaeological structures (Benjelloun et al., 2020). In addition to this localised rupture, numerous other event deposits are present in the sediments (laterally and temporally). We demonstrated that the same earthquake in 1065 CE is associated with various deposit types. One type of deposition is only observed for the 1065 CE earthquake, which takes place in the lake, unlike the others, suggesting that this type of deposition may depend on ground motion parameters besides the source-core distance.A compilation of marine and lacustrine palaeoseismological studies was carried out at the scale of the western part of the NAF. We show that the relationship between sedimentation rate and the presence of earthquake-induced slope destabilisation doesn't work in the marine environment, unlike in the lacustrine environment. We also show that Lake Iznik records earthquakes from the NNAF and the MNAF, whereas the Sea of Marmara records only NNAF earthquakes. These observations open new perspectives and demonstrate the need to consider seismology and site effects in marine and lacustrine paleoseismology.References:Benjelloun, Y., De Sigoyer, J., Dessales, H., Baillet, L., Guéguen, P., Şahin, M., 2020. Historical earthquake scenarios for the middle strand of the North Anatolian Fault deduced from archeo-damage inventory and building deformation modeling. Seismol. Res. Lett. https://doi.org/10.1785/0220200278Gastineau, R., De Sigoyer, J., Sabatier, P., Fabbri, S.C., Anselmetti, F.S., Develle, A.L., Şahin, M., Gündüz, S., Niessen, F., Gebhardt, A.C., 2021. Active Subaquatic Fault Segments in Lake Iznik Along the Middle Strand of the North Anatolian Fault, NW Turkey. Tectonics 40, e2020TC006404. https://doi.org/10.1029/2020tc006404Reilinger, R., McClusky, S., Vernant, P., Lawrence, S., Ergintav, S., Cakmak, R., Ozener, H., Kadirov, F., Guliev, I., Stepanyan, R., others, 2006. GPS constraints on continental deformation in the Africa-Arabia-Eurasia continental collision zone and implications for the dynamics of plate interactions. J. Geophys. Res. Solid Earth 111. https://doi.org/10.1029/2005JB00405
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The Manyas fault zone (MFZ) is a splay fault of the Yenice Gönen Fault, which is located on the southern branch of the North Anatolian Fault System. The MFZ is a 38 km long, WNW–ESE-trending and normal fault zone comprised of three en-echelon segments. On 6 October 1964, an earthquake (Ms = 6.9) occurred on the Salur segment. In this study, paleoseismic trench studies were performed along the Salur segment. Based on these paleoseismic trench studies, at least three earthquakes resulting in a surface rupture within the last 4000 years, including the 1964 earthquake have been identified and dated. The penultimate event can be correlated with the AD 1323 earthquake. There is no archaeological and/or historical record that can be associated with the oldest earthquake dated between BP 3800 ± 600 and BP 2300 ± 200 years. Additionally, the trench study performed to the north of the Salur segment demonstrates paleoliquefaction structures crossing each other. The surface deformation that occurred during the 1964 earthquake is determined primarily to be the consequence of liquefaction. According to the fault plane slip data, the MFZ is a purely normal fault demonstrating a listric geometry with a dip of 64°–74° to the NNE.
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Au cours de la derniere centaine d’annees, la faille nord-anatolienne (FNA) a deja genere 9 seismes de magnitude superieure a 7 en Turquie. Dans cette these nous investiguons la faille de Ganos qui est le segment occidental de la FNA. Cette faille fut responsable du seisme de Murefte du 9 aout 1912 (M 7. 3). La faille de Ganos est visible en surface sur 45-km alors que le reste est en mers Egee a l’est et Marmara a l’ouest. Cette faille de Ganos forme la section occidentale d’une large zone en « step-over » qui correspond au bassin losangique (pull-apart) de Marmara ou le seisme de Kocaeli de 1999 fut localise dans sa partie est. Les deux extremites des ruptures de 1912 et de 1999 definissent une lacune sismique dans la mer de Marmara. Des analyses geomorphologiques sur les 45-km a terre de la faille de Ganos ont permis de decrire des structures typiques des failles en decrochement (ex : pull-apparts, bombements, step-over, rides de compression et decalage de rivieres). La section a terre de la faille de Ganos est d’azimut ~N68°E, segmentee en deux step-over extensifs au niveau de Golcuk and Kavak. La combinaison entre les analyses morphologiques a terre et en mer suggerent un minimum de 04 sous-segments limites par des complexites geometriques qui est de l’est a l’ouest comme suit : Le bassin central de Marmara, le coude de Ganos, step-over de Golcuk, step-over de Kavak and la depression Saros. La depression de Saros et le basin central de Marmara sont les plus importantes complexites structurales le long de la faille de Ganos et peuvent as ir comme barriere a la propagation de la rupture. Le deplacement cumule calcule sur 69 localites, de la reconstruction tectonique permettent d’avoir un apercu sur les caracteristiques de deformation du segment de Ganos a long terme et a court terme. Les mesures des deplacements de chenaux, des cretes et une partie d’ancienne routes nous conduisent a evaluer un decalage entre 8 et 575m. Par ailleurs, nous suggerons un decalage (offset) plus important de 200m a 9000m base sur la reconstruction du systeme hydrologique actuel. Une classification des decalages de chenaux montre 8 classes distinctes d’offset de glissement cumulee. Nous avons aussi utilise les courbes de fluctuations du niveau de la mer noire afin de contraindre les periode de fortes precipitations qui peuvent generer des incisions de chenaux. 5 groupes de glissement cumule (de 70 a 300m) montrent une bonne correlation avec un rehaussement du niveau de la mer consequent a 4 ka, 10. 2 ka, 12. 5 ka, 14. 5 ka et 17. 5 ka. Les estimations du taux de glissement conduisent a un taux de glissement constant de of 17. 9 mm/an pour les dernieres 20. 000 annees et un taux de glissement variable de 17. 7 mm/an, 17. 7 mm/an, 17. 9 mm/an et 18. 9 mm/an pour les dernieres 10. 2 ka, 12. 5 ka, 14. 5 ka et 17. 5 ka, respectivement. La paleosismologie a montre sur 03 sites (Guzelkoy, Yenikoy and Yorguc) des evidences de 8 evenements sismiques, 5 dates entre 1043 – 835 BC et 1500 – 830 BC a Guzelkoy et Yenikoy respectivement. Une meilleure datation a ete contrainte pour les trois derniers evenements a Guzelkoy qui sont vraisemblablement des seismes en (1) 1343 ou 1344 (2) 1659 ou 1766b and (3) 1912. Nous suggerons deux scenarios de recurrence de seismes pour les derniers seismes en relation avec la faille de Ganos. Le scenario (1) conduit a une moyenne de recurrence de 285 ± 36 ans et englobe les evenements de 1912, 1659, 1354/1344, 824, 484 alors que le scenario (2) est aussi valable si une recurrence non periodique des seismes est acceptee. La combinaison entre les analyses geomorphologiques et des resultats des tranchees conduit a un taux de glissement de la faille nord anatolienne au niveau de la region de Ganos. A Guzelkoy deux paleo-chenaux presentement un decalage de 16 m et 21 m et conduit a un taux de 22. 3 ± 0. 5 mm/an pour ce dernier ~700 annees et 26. 9 mm/an pour les 781 dernieres annees respectivement. A Yenikoy des datations des couches les plus profondes montre de 46 ± 1 m de decalage de chenal et donnant ainsi un maximum de 17 mm/an de taux de glissement. Le 9 aout 1912 la region de Murefte a ete secouee par un seisme (M = 7,3) a frappe le long de la faille de Ganos et a provoque de graves degâts (Io = X) entre Tekirdag et de Canakkale. Un deuxieme grand choc s'est produit le 13 Septembre 1912 (M = 6,8) avec une zone epicentrale a l'ouest du choc principal, causant des destruction Io = VII a l'ouest de dommages Gazikoy et le long de la peninsule de Gallipoli. Des rupture en surface ont ete enregistrees le long de la totalite des 45-km de la section en surface. Nous avons determine un glissement maximum de 5,5 m qui a ete precedemment suggere a 3 m par Ambraseys & Finkel et al. (1987). Nous prolongeons les mesures de glissement de Altunel et al. (2004) a partir de 31 localites a 45 avec une meilleure repartition le long de la faille. La distribution d’offsets indique qu'une certaine partie de la rupture est au large, c'est a dire dans la baie de Saros et Mer de Marmara. 73 enregistrement de sismogrammes historiques ont ete collectes pour les evenements du 9 aout, 10 aout et le 13 Septembre 1912. Des paires comparables ont ete numerisees a l'aide du logiciels TESEO. La modelisation et deconvolution de la forme d'ondes sismiques a permis la recuperation d'une fonction temps source en utilisant les evenements du 13 Septembre et du 9 Aout et fourni une fonction temps source de 40 secondes pendant le tremblement de terre du 9 aout. Considerant une propagation unilaterale de la rupture de 3 km/s, cette duree implique longueur de rupture de 120 km, coherente avec la dimension du seisme (Mw 7. 4). Les polarites P des ondes a 5 stations et des N68°E d’azimut de faille nous permet de deduire un mecanisme au foyer pour l’evenement du 9 aout. L'ampleur du choc Septembre 13 exige 30 ± 10 km de rupture de surface et des contraint la terminaison ouest pour les 120 ± 20km de longueur de la rupture du 9 Aout. Prenant en compte les deux evenements, une position de l'epicentre dans la baie de Saros pour le choc du 13 septembre de 150 ± 20 km de longueur totale de rupture et s'etendrait de Saros en propageant vers l’est et rejoignant ainsi le bassin de Marmara central, en accord avec la complexite geometriques importantes le long de cette section de la faille nord-anatolienne. Par consequent, la terminaison est de la rupture du 09 aout 1912 et la terminaison ouest de la rupture de 1999 impliquent un minimum de 100-km de lacune sismique dans la mer de Marmara. Cette longueur de faille suggere un seisme de magnitude M>7 qui devra etre pris en compte dans l’evaluation du risque sismique de la region d’Istanbul.
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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 N70°E, 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 ± 0.5 m and 35.4 ± 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) 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 ± 1.5 m next to the fault, and 21.3 ± 1.5 m total channel deflection. Radiocarbon dating of past channel units and fault scarp‐related colluvial deposits imply an average 17 +/− 5 mm/year slip rate and 323 ± 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.
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The Ezinepazarı Fault (EPF) is an active segment that restricts the Niksar Basin in the central part of the North Anatolian Fault Zone and has been the source of the devastating Mw 8.0 earthquake in the last 100 years. Traces of the surface rupture of the EPF, which occurred in AD 1939, can still be observed in the field today as a right-lateral strike-slip character. While paleoseismological studies were mostly focused on the western part of the North Anatolian Fault Zone (NAFZ) in previous studies, the studies on the central and eastern parts of the NAFZ are rarely addressed. In this context, trench-based paleoseismology studies were carried out on the surface rupture traces in order to determine both historical/prehistoric earthquakes caused by the fault and the Quaternary period characteristics of the EPF. According to the data obtained, at least two historical earthquake activities have been detected besides the last 1939 earthquake on the EPF. Accordingly, the first and second events occurred in E1: 5871 ± 2300 BP and E2: 1651 ± 128 BP, respectively. When the determined data are compared with the historical earthquake catalogs, it is concluded that Event 2 (E2) can be correlated with the AD 343 Niksar earthquake; thus, the EPF has an irregular earthquake recurrence interval.
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Paleoseismology of the Sürgü and Çardak faults - splays of the Eastern Anatolian Fault Zone, Türkiye
The sinistral East Anatolian Fault Zone (EAFZ) and the dextral North Anatolian Fault Zone (NAFZ) are two important strike-slip faults that delimit the boundaries of the Anatolian plate. The north-south directed compressional forces in eastern Türkiye trigger the westward escape of the Anatolian plate along these prominent structures. This study aims to reveal the earthquake history of the Sürgü and Çardak faults, which are important fault segments that splay from the EAFZ. In this context, overall, four paleoseismologic trenches were dug, two trenches on the Sürgü Fault and two trenches on the Çardak Fault. Along the Sürgü Fault, at least two paleoearthquake events have been determined on the trench walls, one event occurred around 3400 BCE and the second event happened between 2085 ± 65 BCE and 790 ± 20 BCE. Moreover, trenching results from the Çardak Fault indicate two surface rupturing paleoearthquakes between 10520 ± 95 BCE and 5780 ± 65 BCE, and between 3215 ± 125 BCE and 825 ± 55 CE, respectively. The focal mechanisms of important instrumental earthquakes around the Sürgü and Çardak faults on the EAFZ show that NNE-SSW trending compressional forces are actively dominating the tectonic setting of the region in the contemporary era. Paleoseismological investigations suggested that the Sürgü and Çardak faults have the potential to produce surface-rupturing earthquakes with an estimated magnitude of 7 or larger.
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The Ganos fault that ruptured on 9 August 1912 (Mw: 7.4) is the westernmost inland segment of the North Anatolian fault (NAF). Here, the Ganos fault is bounded at its two tips with offshore faults segments, in the Sea of Marmara to the east and the Gulf of Saros to the west in the North Aegean Trough. Therefore, the paleoseismology of the 45-km-long inland fault is of importance to the seismic hazard analysis related to offshore active faults and in particular for the seismic gap in the Marmara Region. Earlier studies have established an earthquake chronology for the western and eastern inland tips of the Ganos fault. Here, we extend the paleoseismic studies toward the central segment. Three trenches at Yörgüç have revealed evidence for two faulting events, possibly post-1669 CE ±30 years, which can be correlated to the 1659 or 1766, and the 1912 historical earthquakes. At Yeniköy, we determined an offset of 46 ± 1 m and 47 ± 1 m on a stream channel and a ridge-crest, respectively. In two trenches we determined two faulting events for the last 1000 years and seven events for the last 3500 years. In trench T5, the base of the displaced stream channel provides a calibrated date of 829?591 BCE. Using the 46 ± 1 m right-lateral displacement, we calculate a slip rate of 16.9 ± 0.7 mm/year for the last 2732 ± 119 years. A combined analysis with earlier paleoseismic studies on the Ganos fault suggests that the historical earthquakes of 1912, 1766b or 1659, 1354 or 1343a, and 1063 ruptured the entire inland fault section. In such a case, the recurrence interval for this section of the NAF corresponds to 283 ± 81 years. Combining earlier estimations, we suggest an average slip rate of 17.1 ± 0.9 mm/year for the last 2700 years and observe a characteristic slip behavior of 4.5 to 5 m per event for this section of the North Anatolian plate boundary fault.
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