Late Quaternary co-seismic sedimentation in the Sea of Marmara's deep basins

25 pages, 15 figures, 1 tableauInternational audienceThe deep, northern, part of the Sea of Marmara (northwestern Turkey) is composed of several aligned, actively subsiding, basins, which are the direct structural and morphological expression of the North Anatolian Fault's northern branch. The last 20 kyr of their sedimentary fill (lacustrine before 12 kyr BP) have been investigated through giant piston coring onboard R/V MARION-DUFRESNE (MARMACORE Cruise, 2001) and chirp subbottom profiler onboard R/V ATALANTE during MARMARASCARPS Cruise (2002). Especially during the lacustrine stage, the infilling of the deep basins (Tekirda?, Central, Kumburgaz, and Çinarcic Basins; up to 1250 m depth) was dominated by turbidites (with coarse mixed siliciclastic and bioclastic basal part), intercalated in “hemipelagic-type” finegrained calcareous and slightly siliceous clays. Often – especially in the thickest ones – the turbidites show strong segregation and a sharp boundary between coarse part and suspendedload part. In the Central Basin, 8 m of a unique sedimentary event include a 5 to 8m-thick “homogenite” well imaged on seismic profiles. The latter is interpreted as related to a major – possibly triggered - tsunami effect, as described in the Eastern Mediterranean by Kastens and Cita (1981). In the marine (Holocene) upper part of the sedimentary fill, repeated to-and-from structures, affecting silt or fine sand, are evidencing seiche-like effects and, thus, earthquake triggering. Detailed correlations between two deep coring sites (1250 and 1200 m) indicate more than 100 % overthickening in the deepest one; this implies specific processes of distribution of terrigenous input by dense hyperpycnal currents (high kinetic energy, seiche effect, complex reflections on steep slopes). The peculiar sedimentary infilling of the Sea of Marmara's Central Basin (and, by extrapolation, of the whole set) is tentatively interpreted as a direct consequence of the strong seismic activity; the imprint of the latter is more obvious prior to the base of the Holocene, as environmental conditions favoured marginal accumulation (especially on the southern shelf) of large amounts of erosion products available for mass wasting

The Sea of Marmara pull-apart (North Anatolian Fault) (morphologic and tectonic evolution, fault interactions, and seismic hazard in the region of Istanbul)

Des escarpements sismiques associés aux événements historiques récents ontété découverts sur le plancher du pull-apart de la Mer de Marmara, le longde la Faille Nord Anatolienne (FNA). La campagne MARMARASCARPS utilisantun submersible (ROV) fournit des observations directes pour étudier lamorphologie et la géologie de ces escarpements. Ces observations sontcritiques pour définir les barrières qui arrêtèrent les ruptures sismiquespassées (1894, 1912, 1999, M > 7). L identification d une rupture continuesur plus de 60 km avec un déplacement dextre de 5m, probablement associéeau séisme de Ganos (1912, Ms 7.4), modifie notre connaissance de la chargeactuelle près de la ville d Istanbul. L évolution morphologique desescarpements de faille à composante normale est modélisée par deuxprocessus de diffusion (érosive et sédimentaire) en interaction avec ledéplacement vertical sur les failles. Le modèle proposé permet d estimerl âge des escarpements sous-marins associés aux séismes historiques (1766)et de discuter l âge du pull-apart de Marmara (2-6 Ma). Enfin, notreconnaissance des séismes du 18ème siècle à nos jours (M > 7), de lagéologie et de la cinématique des failles est utilisée pour analyser lesconditions favorisant le déclenchement de séismes majeurs isolés, enessaims ou encore en séquences se propageant le long du systèmeFNA-Marmara. Des modèles de Coulomb sont utilisés pour discuter ladistribution spatio-temporelle des séismes. Les séquences de propagationne se produisent pas à chaque cycle sismique le long de la FNALepull-apart de Marmara se comporte comme une complexité géométriquemajeure, arrêtant ou retardant la propagation de séquences. Earthquake scarps associated with recent historical events have been foundon the floor of the Sea of Marmara pull-apart, along the North AnatolianFault (NAF). The MARMARASCARPS cruise using an unmanned submersible (ROV)provides direct observations to study the morphology and geology of thosescarps, their distribution and geometry. These observations are criticalto define barriers that have arrested past earthquakes along the submarinefault system (1894, 1912, 1999, M > 7). The identification of a breakcontinuous over 60 km with a right-lateral slip of 5 m, probablyassociated with the Ganos earthquake (1912, Ms 7.4), modifiessubstantially our understanding of the current state of loading along theNAF next to Istanbul. The morphologic evolution of normal fault scarps ismodelled by two processes of diffusion (erosive and sedimentary)interacting with the vertical displacement along faults. The proposedmodel enables to estimate the age of submarine fault scarps associatedwith historical earthquakes (1766) and to discuss the age of the Sea ofMarmara pull-apart (2-6 Ma). Finally, knowledge on large earthquakes sincethe 18th century (M > 7), geology and fault kinematics is used to analyseconditions that favour isolated seismicity, clustered earthquakes orpropagating sequences along the NAF-Marmara fault system. Coulomb stressmodels are used to discuss the distribution of earthquakes in space andtime. Propagating earthquake sequences do not occur every seismic cyclealong the NAF. The Marmara pull-apart fault system behaves as a majorgeometric complexity, stopping or delaying the progression of earthquakeclustering and propagating sequencesPARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF

Fault interactions in the Sea of Marmara pull-apart (North Anatolian Fault): earthquake clustering and propagating earthquake sequences

International audienceKnowledge on large earthquakes (M ≥ 7.0), geology and fault kinematics is used to analyse conditions that favour isolated seismicity, clustered earthquakes or propagating sequences along the North Anatolian Fault (NAF) and the Sea of Marmara pull-apart. The overall NAF– Marmara fault system is one of the most appropriate on Earth to document fault interactions because reliable information covers almost completely two seismic cycles (the past ∼500 yr). Coulomb stress analysis is used to characterize loading evolution in well-identified fault segments, including secular loading from below and lateral loading imposed by the occurrence of previous earthquakes. Earthquakes along the NAF tend to occur where previous events have increased the stress, but significant isolated events in the Sea of Marmara region (1894, 1912) have occurred, suggesting the secular loading has been the determining factor. Present-day loading appears to be particularly high along the 70-km-long segment located in the central Marmara Sea, southwest of Istanbul. For the 18th century M ≥ 7.0 earthquake clusters, we construct scenarios consistent with the tectonic and historical data. We find that scenarios consistent with slip deficit and secular loading distributions (from below) clearly involve a sequence that propagates westward through the Sea of Marmara, despite the structural complexity. However, the inference of a propagating sequence implies that each event has occurred in a segment previously stressed by lateral Coulomb stress interactions. The most likely scenarios for the propagating sequence are also consistent with Coulomb stress interactions between faults with significant normal slip across the Cinarcik basin. Propagating earthquake sequences do not occur every seismic cycle along the NAF. The loading has to be in a particular state of stress close to failure and uniform all along the fault segments to experience propagating earthquake sequences. Non-uniform stress relief during the 18th century sequence explains the occurrence of isolated events in Marmara in 1894 and 1912. As a consequence, the wellknown 20th century sequence along the NAF has not propagated as a sequence across the Sea of Marmara. The most linear part of the NAF across northern Turkey behaves as a single fault segment, accumulating stress during hundreds of years and rupturing entirely during very short periods. The Marmara pull-apart fault system behaves as a major geometric complexity, stopping or delaying the progression of earthquake clustering and propagating sequences. Fault zones interact with each other at a very large scal

40.Characterization of Submarine Earthquake Sources and Paleoseismic Records on the New Zealand Continental Shelf and Slope

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