Analyses des vitesses et des déplacements co-sismiques sur des failles décrochantes en Mongolie et en Iran - Approche morphotectonique et paléosismologique

The aim of this thesis is to analyze the variations in slip rates along strike-slip faults, in intracontinental domain, producing large earthquakes (M > 7.5). To illustrate these variations, this work has focused in two area located in the most tectonically active continental domains in the world: in the western part of Mongolia (Bogd and Bulnay faults) and in the northern part of Iran (Astaneh and Tabriz faults). Using morphotectonic and paleoseismological analyses, the kinematics, the slip rates and the recurrence times have been estimated and allow us to describe the characteristics of seismic cycle along these faults. In Mongolia, the slip rates are estimated at ~ 1,2 and ~ 2,6 mm/yr along the Bogd and the Bulnay faults, respectively, with no variations of geological slip rates over the late Pleistocene-Holocene period. These two faults present characteristic slips and similar recurrence times between large earthquakes. The paleoseismological investigations suggest that a cluster occurred 3000 years ago, similar to the seismic cluster recorded in Mongolia during the XX century. In Iran, the slip rate was estimated to 2 mm/yr along the Astaneh fault and the recurrence times are ranging from 1600 to 2200 years, associated with offsets comprised between 3 and 4,5 m. We have also estimated a slip rate of ~ 7 mm/yr along the Tabriz fault, in agreement with the present day rate estimated by GPS, suggesting no variations in the slip rate over the past 45 ka.Ce travail de thèse a pour but d'analyser les variations de vitesses sur des grandes failles décrochantes en contexte intracontinental, capables de produire des séismes de très fortes magnitudes (M > 7.5). Afin d'illustrer ces variations d'activités, cette analyse a été effectuée sur deux zones d'études situées en domaine continental et sismiquement actives: la région ouest de la Mongolie (failles de Bogd et Bolnay) et le nord de l'Iran (failles d'Astaneh et de Tabriz). À partir d'une approche morphotectonique et paléosismologique, les cinématiques, les vitesses de failles et les intervalles de récurrence entre les séismes majeurs ont été estimés, permettant d'analyser les caractéristiques du cycle sismique sur chacune des failles. En Mongolie, les failles de Bogd et Bolnay présentent respectivement des vitesses de ~ 1,2 et 2,6 mm/an, qui semblent être constantes sur la période Pleistocène supérieur-Holocène. Ces deux failles présentent également des glissements caractéristiques et des intervalles de temps similaires entre les séismes majeurs. Les analyses paléosismologiques suggèrent qu'un essaim sismique comparable à celui enregistré au XXème siècle a eu lieu il y a environ 3000 ans. En Iran, une vitesse géologique de 2 mm/an a été estimée sur la faille d'Astaneh et les données paléosismologiques suggèrent des intervalles de récurrence de 1800 ans, associés à des déplacements en surface compris entre 3 et 4,5 m. Nous avons également estimé une vitesse de 7 mm/an sur la faille de Tabriz, en accord avec les données GPS, suggérant que la vitesse sur cette faille est constante depuis 45 ka

Optically stimulated luminescence dating and terrestrial Cosmogenic Nuclides in active tectonics: comparing apples to oranges?

International audienc

How to reconcile OSL and TCN data: the potential of high-resolution sampling on the Choushui Tableland (West Central Taiwan)

International audienc

How to reconcile OSL and TCN data: the potential of high-resolution sampling on the Choushui Tableland (West Central Taiwan)

International audienc

Détermination de l'aléa sismique : l'approche paléosismologique

Pour calculer la probabilité d'un futur séisme partiellement destructeur..

ESR and OSL variability in quartz extracted from magmatic, metamorphic or sedimentary rock

International audienceSediment routing systems in fluvial catchments are primarily governed by intertwined climatic, tectonic and man-induced drivers at the centennial/millennial timescales. Among the various geomor-phological and geochemical approaches developed to trace sediment dynamics, the scientific commu-nity has recently explored the potential of (palaeo-)dosimetric methods, which are extensively used to date e.g. Quaternary alluvial environments. Recently, Optically Stimulated Luminescence (OSL) and Electron Spin Resonance (ESR) signals have been successfully transposed to decipher sediment prove-nance and transport in fluvial catchments. In this context, the French ANR QUARTZ research project aims at using quartz grains as an ubiquitous marker of sediment dynamics to understand (i) how each quartz grain holds a source-specific signature, and (ii) how this signature evolves along sediment routing systems. This contribu-tion specifically focuses on the first research topic.Quartz-bearing rocks located upstream in catchments deliver the material that is usually dated by OSL and/or ESR in fluvial sequences/deposits for geological or archaeological purposes. Here, we ana-lyzed with ESR and OSL methods quartz grains originating from different source rocks in the Streng-bach and Séveraisse catchments (France), draining a low mountain range (Vosges Mountains) and the Alps (Ecrins Massif), respectively. These rocks comprise magmatic, metamorphic and sedimentary lithologies of distinct age and composition, and provide quartz minerals present in the transposed and deposited sediments. The quartz grains were analyzed with ESR and OSL methods on the quartz min-erals from different quartz-bearing rock formations in both catchments, i.e. mostly granites, gneisses and sandstones of distinct ages and/or compositions. The source-specific signature of the different ESR signals (Ti/Al ratio, signal shape, non-optically bleachable intensity of the Al centre) was investigated. The bleaching kinetics of the different ESR centres used in dating and present in these quartz from different rock types were also investigated. Depending on the history of the quartz-bearing rock and therefore of the quartz nature (magmatic, metamorphic or sedimentary), we suggest that the ESR re-sponse varies in terms of signal shapes and intensity ratios of the different centres measured. Similar-ly, quartz OSL characteristics have been investigated (OSL signal intensities, contributions of fast/medium/slow OSL components, dose-response curves and saturation behavior) between rocks of different origins, as well as the bleaching potential (residual doses) between different quartz origins. These analyses are currently complemented in a near future by quantified trace element analyses on quartz samples from the same sources. This will allow us not only to provide encouraging results in terms of tracing quartz in fluvial deposits, but also a better understanding of the processes at the origin of ESR and OSL signals variability. This will constitute a first step towards understanding the dosi-metric behaviour of the sediments to be dated, and towards even more reliable dating techniques

ESR and OSL variability in quartz extracted from magmatic, metamorphic or sedimentary rock

International audienceSediment routing systems in fluvial catchments are primarily governed by intertwined climatic, tectonic and man-induced drivers at the centennial/millennial timescales. Among the various geomor-phological and geochemical approaches developed to trace sediment dynamics, the scientific commu-nity has recently explored the potential of (palaeo-)dosimetric methods, which are extensively used to date e.g. Quaternary alluvial environments. Recently, Optically Stimulated Luminescence (OSL) and Electron Spin Resonance (ESR) signals have been successfully transposed to decipher sediment prove-nance and transport in fluvial catchments. In this context, the French ANR QUARTZ research project aims at using quartz grains as an ubiquitous marker of sediment dynamics to understand (i) how each quartz grain holds a source-specific signature, and (ii) how this signature evolves along sediment routing systems. This contribu-tion specifically focuses on the first research topic.Quartz-bearing rocks located upstream in catchments deliver the material that is usually dated by OSL and/or ESR in fluvial sequences/deposits for geological or archaeological purposes. Here, we ana-lyzed with ESR and OSL methods quartz grains originating from different source rocks in the Streng-bach and Séveraisse catchments (France), draining a low mountain range (Vosges Mountains) and the Alps (Ecrins Massif), respectively. These rocks comprise magmatic, metamorphic and sedimentary lithologies of distinct age and composition, and provide quartz minerals present in the transposed and deposited sediments. The quartz grains were analyzed with ESR and OSL methods on the quartz min-erals from different quartz-bearing rock formations in both catchments, i.e. mostly granites, gneisses and sandstones of distinct ages and/or compositions. The source-specific signature of the different ESR signals (Ti/Al ratio, signal shape, non-optically bleachable intensity of the Al centre) was investigated. The bleaching kinetics of the different ESR centres used in dating and present in these quartz from different rock types were also investigated. Depending on the history of the quartz-bearing rock and therefore of the quartz nature (magmatic, metamorphic or sedimentary), we suggest that the ESR re-sponse varies in terms of signal shapes and intensity ratios of the different centres measured. Similar-ly, quartz OSL characteristics have been investigated (OSL signal intensities, contributions of fast/medium/slow OSL components, dose-response curves and saturation behavior) between rocks of different origins, as well as the bleaching potential (residual doses) between different quartz origins. These analyses are currently complemented in a near future by quantified trace element analyses on quartz samples from the same sources. This will allow us not only to provide encouraging results in terms of tracing quartz in fluvial deposits, but also a better understanding of the processes at the origin of ESR and OSL signals variability. This will constitute a first step towards understanding the dosi-metric behaviour of the sediments to be dated, and towards even more reliable dating techniques