Carbone des sols en Afrique

Les sols sont une ressource essentielle à préserver pour la production d’aliments, de fibres, de biomasse, pour la filtration de l’eau, la préservation de la biodiversité et le stockage du carbone. En tant que réservoirs de carbone, les sols sont par ailleurs appelés à jouer un rôle primordial dans la lutte contre l’augmentation de la concentration de gaz à effet de serre. Ils sont ainsi au centre des objectifs de développement durable (ODD) des Nations unies, notamment les ODD 2 « Faim zéro », 13 « Lutte contre le changement climatique », 15 « Vie terrestre », 12 « Consommation et production responsables » ou encore 1 « Pas de pauvreté ». Cet ouvrage présente un état des lieux des sols africains dans toute leur diversité, mais au-delà, il documente les capacités de stockage de carbone selon les types de sols et leurs usages en Afrique. Il propose également des recommandations autour de l’acquisition et de l’interprétation des données, ainsi que des options pour préserver, voire augmenter les stocks de carbone dans les sols. Tous les chercheurs et acteurs du développement impliqués dans les recherches sur le rôle du carbone des sols sont concernés par cette synthèse collective. Fruit d’une collaboration entre chercheurs africains et européens, ce livre insiste sur la nécessité de prendre en compte la grande variété des contextes agricoles et forestiers africains pour améliorer nos connaissances sur les capacités de stockage de carbone des sols et lutter contre le changement climatique

The middle strand of the North Anatolian fault in Iznik region : insights from geomorphology and archeoseismology

La faille nord anatolienne (NAF), une zone de faille dextre longue de 1000 km est caractérisée par un fort aléa sismique. Elle accommode le mouvement vers l’ouest de l’Anatolie par rapport à l’Eurasie. Dans sa partie ouest, la NAF se divise en trois branches, dont une borde le sud de la mer de Marmara et du lac d’Iznik. Ce segment médian de la NAF (MNAF) présente aujourd’hui une très faible sismicité. Pourtant, cette zone se caractérise par un risque sismique élevé à l’échelle des deux derniers millénaires. Plus de six séismes sont décrits par les auteurs anciens et causèrent des destructions dans la ville d’Iznik (ancienne Nicée), un centre politique et religieux important aux époques hellénistique et romaine. Notre étude a pour but de contraindre l’activité sismique récente de la MNAF dans la région d’Iznik à plusieurs échelles de temps, par une approche pluridisciplinaire combinant géosciences et archéologie.Le premier objectif de cette thèse est de développer l’étude des bâtiments anciens comme archives de la sismicité historique en observant leurs endommagements et réparations successifs. La ville de Nicée est appropriée pour ce type d’étude puisqu’elle présente plusieurs bâtiments préservés portant les traces de nombreuses réparations. J’ai concentré mon travail sur des infrastructures critiques comme la muraille défensive longue de 3 km. Cela inclut aussi l’aqueduc de la ville, recoupé par une faille active, ainsi qu’une basilique romaine découverte récemment sous les eaux du lac d’Iznik à 20 m de la côte. En appliquant plusieurs techniques de datation (stratigraphie des édifices, 14C) sur les bâtiments, j’ai pu identifier au moins trois séismes sources d’endommagement depuis le 6e siècle. La répartition des dommages sur les bâtiments permet d’estimer des intensités locales de VIII sur l’échelle macrosismique européenne (EMS98). Grâce à des simulations numériques, je montre que les déformations visibles sur un obélisque romain au nord d’Iznik sont compatibles avec des magnitudes proches de Mw 7 pour des distances épicentrales inférieures à 15 km.Le deuxième objectif de cette thèse est de contraindre la vitesse de glissement quaternaire sur la MNAF et de mieux comprendre la formation du lac d’Iznik à l’ouest de la ville. Ce lac de 313 km² est le plus grand lac d’eau douce de la région de Marmara. Les principales failles autour du lac ont été cartées avec un MNT de haute résolution dérivé d’images Pléiades. Les marqueurs géomorphologiques décalés par la MNAF ont fait l’objet de mesures systématiques. L’analyse statistique de ces décalages a mis en évidence six ruptures majeures préservées dans le paysage, avec des déplacements cosismiques entre 2 et 6 m. Les âges de trois niveaux de terrasses lacustres au nord du lac ont été quantifiés par radiocarbone et 10Be produit in situ. J’ai pu déterminer un taux de glissement horizontal minimum de 2.9 mm/yr. Le basculement vers le sud des paléorivages est compatible avec un taux de glissement vertical élevé sur la MNAF autour de 6 mm/yr.En travaillant sur la morphologie et les lithologies de la région d’Iznik, nous avons découvert des preuves d’épisodes glaciaires LGM. La morphologie en U de plusieurs vallées à l’est du lac d’Iznik, séparées par des sauts topographiques correspond à l’empreinte d’anciens glaciers. Cette hypothèse est confirmée par la présence de moraines en bord de vallée, de blocs erratiques aux lithologies variées, et de sédiments glacio-lacustres. La distribution spatiale de ces marqueurs morphologiques et lithologiques nous permet de reconstruire l’emplacement et le retrait vers l’est de ce glacier. Les âges absolus des dépôts glaciaires et des alluvions postérieurs à la glaciation sont compatibles avec des proxies paléoenvironnementaux provenant du lac d’Iznik et les études réalisées sur d’autres glaciers turcs LGM. Il s’agit de la première découverte de glaciers à si basse altitude en Turquie.The North Anatolian fault (NAF), a 1000 km-long dextral fault zone is known for its strong seismic hazard. It accommodates the westward motion of Anatolia, relative to Eurasia. In its western part, the NAF splits into three strands, one of which passing south of the Marmara sea and the Iznik lake. This NAF middle strand (MNAF) shows nowadays a very low seismic activity. However, this area has been characterized by a significant earthquake hazard over the last two millennia. Several ancient authors mention the occurrence of more than six destructive earthquakes that impacted Iznik (old Nicaea), which was an important political and religious centre during the Hellenistic and Roman periods. Our study aims to constrain the recent seismic activity on the MNAF in the Iznik area at different time scales through a multidisciplinary approach coupling earth science and archeology.The first goal of this thesis is to develop the study of ancient buildings as archives of the historical seismicity by observing their successive damages and repairs. The city of Nicaea is appropriate for this kind of study as it presents several well preserved ancient buildings that bear traces of numerous repairs. I focus my study on the critical infrastructures for the city such as the 3 km-long protecting walls. This also includes the aqueduct that provided the city with water and is crossed by a segment of active fault, and a Roman basilica recently discovered underwater in the Iznik lake 20 m far from the shore. Applying different dating techniques (stratigraphy of the archaeological building, 14C) to the various materials of these buildings (terra cotta, mortar, concretions on the aqueduct), I was able to identify at least three damaging earthquakes since the 6th century AD. The amount of damage on these buildings allows to estimate local intensities at VIII on the European macroseismic scale (EMS98). Thanks to numerical simulations, I show that the current deformation visible on a Roman obelisk north of Iznik is compatible with magnitudes close to Mw 7 for epicentral distances smaller than 15 km.The second goal of this thesis is to constrain the Quaternary slip rate on the MNAF and better understand the formation of Iznik Lake, a 313 km²-large lake located just west of the city, which is the largest freshwater lake in the Marmara region. The main faults around the lake were mapped using a high-resolution DEM derived from Pleiades images. Geomorphic markers offset by the MNAF were systematically measured. The statistical analysis of the offsets revealed six major ruptures preserved in the landscape, with coseismic displacements between 2 and 6 m. The ages of three levels of lacustrine terraces north of the lake were quantified by radiocarbon and in-situ produced 10Be. A minimal horizontal slip rate of 2.9 mm/yr was estimated. The southward tilting of the lake paeloshorelines is compatible with a high vertical slip rate on the MNAF around 6 mm/yr.While working on the morphology and lithologies of the Iznik area, we have discovered significant evidence for LGM glacial events. The U-shaped morphology of several successive valleys east of Iznik Lake separated by topographic highs is interpreted as the print of past glaciers. This is confirmed by the presence of moraine deposits on the sides of the valleys, erratic blocks from various lithologies and glacio-lacustrine sediments. The geographical distribution of these morphological and lithological markers enabled us to reconstruct the former location and eastward retreat of this glacier. The absolute ages obtained from glacial deposits and alluvial sediments postponing the glaciation are compatible with paleoenvironmental proxies in Iznik Lake and previous studies of other Turkish LGM glaciers. This constitutes the first evidence of glaciation at low elevations in Turkey

La branche médiane de la faille Nord Anatolienne dans la région d'Iznik : apports de la géomorphologie et de l'archéosismologie

The North Anatolian fault (NAF), a 1000 km-long dextral fault zone is known for its strong seismic hazard. It accommodates the westward motion of Anatolia, relative to Eurasia. In its western part, the NAF splits into three strands, one of which passing south of the Marmara sea and the Iznik lake. This NAF middle strand (MNAF) shows nowadays a very low seismic activity. However, this area has been characterized by a significant earthquake hazard over the last two millennia. Several ancient authors mention the occurrence of more than six destructive earthquakes that impacted Iznik (old Nicaea), which was an important political and religious centre during the Hellenistic and Roman periods. Our study aims to constrain the recent seismic activity on the MNAF in the Iznik area at different time scales through a multidisciplinary approach coupling earth science and archeology.The first goal of this thesis is to develop the study of ancient buildings as archives of the historical seismicity by observing their successive damages and repairs. The city of Nicaea is appropriate for this kind of study as it presents several well preserved ancient buildings that bear traces of numerous repairs. I focus my study on the critical infrastructures for the city such as the 3 km-long protecting walls. This also includes the aqueduct that provided the city with water and is crossed by a segment of active fault, and a Roman basilica recently discovered underwater in the Iznik lake 20 m far from the shore. Applying different dating techniques (stratigraphy of the archaeological building, 14C) to the various materials of these buildings (terra cotta, mortar, concretions on the aqueduct), I was able to identify at least three damaging earthquakes since the 6th century AD. The amount of damage on these buildings allows to estimate local intensities at VIII on the European macroseismic scale (EMS98). Thanks to numerical simulations, I show that the current deformation visible on a Roman obelisk north of Iznik is compatible with magnitudes close to Mw 7 for epicentral distances smaller than 15 km.The second goal of this thesis is to constrain the Quaternary slip rate on the MNAF and better understand the formation of Iznik Lake, a 313 km²-large lake located just west of the city, which is the largest freshwater lake in the Marmara region. The main faults around the lake were mapped using a high-resolution DEM derived from Pleiades images. Geomorphic markers offset by the MNAF were systematically measured. The statistical analysis of the offsets revealed six major ruptures preserved in the landscape, with coseismic displacements between 2 and 6 m. The ages of three levels of lacustrine terraces north of the lake were quantified by radiocarbon and in-situ produced 10Be. A minimal horizontal slip rate of 2.9 mm/yr was estimated. The southward tilting of the lake paeloshorelines is compatible with a high vertical slip rate on the MNAF around 6 mm/yr.While working on the morphology and lithologies of the Iznik area, we have discovered significant evidence for LGM glacial events. The U-shaped morphology of several successive valleys east of Iznik Lake separated by topographic highs is interpreted as the print of past glaciers. This is confirmed by the presence of moraine deposits on the sides of the valleys, erratic blocks from various lithologies and glacio-lacustrine sediments. The geographical distribution of these morphological and lithological markers enabled us to reconstruct the former location and eastward retreat of this glacier. The absolute ages obtained from glacial deposits and alluvial sediments postponing the glaciation are compatible with paleoenvironmental proxies in Iznik Lake and previous studies of other Turkish LGM glaciers. This constitutes the first evidence of glaciation at low elevations in Turkey.La faille nord anatolienne (NAF), une zone de faille dextre longue de 1000 km est caractérisée par un fort aléa sismique. Elle accommode le mouvement vers l’ouest de l’Anatolie par rapport à l’Eurasie. Dans sa partie ouest, la NAF se divise en trois branches, dont une borde le sud de la mer de Marmara et du lac d’Iznik. Ce segment médian de la NAF (MNAF) présente aujourd’hui une très faible sismicité. Pourtant, cette zone se caractérise par un risque sismique élevé à l’échelle des deux derniers millénaires. Plus de six séismes sont décrits par les auteurs anciens et causèrent des destructions dans la ville d’Iznik (ancienne Nicée), un centre politique et religieux important aux époques hellénistique et romaine. Notre étude a pour but de contraindre l’activité sismique récente de la MNAF dans la région d’Iznik à plusieurs échelles de temps, par une approche pluridisciplinaire combinant géosciences et archéologie.Le premier objectif de cette thèse est de développer l’étude des bâtiments anciens comme archives de la sismicité historique en observant leurs endommagements et réparations successifs. La ville de Nicée est appropriée pour ce type d’étude puisqu’elle présente plusieurs bâtiments préservés portant les traces de nombreuses réparations. J’ai concentré mon travail sur des infrastructures critiques comme la muraille défensive longue de 3 km. Cela inclut aussi l’aqueduc de la ville, recoupé par une faille active, ainsi qu’une basilique romaine découverte récemment sous les eaux du lac d’Iznik à 20 m de la côte. En appliquant plusieurs techniques de datation (stratigraphie des édifices, 14C) sur les bâtiments, j’ai pu identifier au moins trois séismes sources d’endommagement depuis le 6e siècle. La répartition des dommages sur les bâtiments permet d’estimer des intensités locales de VIII sur l’échelle macrosismique européenne (EMS98). Grâce à des simulations numériques, je montre que les déformations visibles sur un obélisque romain au nord d’Iznik sont compatibles avec des magnitudes proches de Mw 7 pour des distances épicentrales inférieures à 15 km.Le deuxième objectif de cette thèse est de contraindre la vitesse de glissement quaternaire sur la MNAF et de mieux comprendre la formation du lac d’Iznik à l’ouest de la ville. Ce lac de 313 km² est le plus grand lac d’eau douce de la région de Marmara. Les principales failles autour du lac ont été cartées avec un MNT de haute résolution dérivé d’images Pléiades. Les marqueurs géomorphologiques décalés par la MNAF ont fait l’objet de mesures systématiques. L’analyse statistique de ces décalages a mis en évidence six ruptures majeures préservées dans le paysage, avec des déplacements cosismiques entre 2 et 6 m. Les âges de trois niveaux de terrasses lacustres au nord du lac ont été quantifiés par radiocarbone et 10Be produit in situ. J’ai pu déterminer un taux de glissement horizontal minimum de 2.9 mm/yr. Le basculement vers le sud des paléorivages est compatible avec un taux de glissement vertical élevé sur la MNAF autour de 6 mm/yr.En travaillant sur la morphologie et les lithologies de la région d’Iznik, nous avons découvert des preuves d’épisodes glaciaires LGM. La morphologie en U de plusieurs vallées à l’est du lac d’Iznik, séparées par des sauts topographiques correspond à l’empreinte d’anciens glaciers. Cette hypothèse est confirmée par la présence de moraines en bord de vallée, de blocs erratiques aux lithologies variées, et de sédiments glacio-lacustres. La distribution spatiale de ces marqueurs morphologiques et lithologiques nous permet de reconstruire l’emplacement et le retrait vers l’est de ce glacier. Les âges absolus des dépôts glaciaires et des alluvions postérieurs à la glaciation sont compatibles avec des proxies paléoenvironnementaux provenant du lac d’Iznik et les études réalisées sur d’autres glaciers turcs LGM. Il s’agit de la première découverte de glaciers à si basse altitude en Turquie

Characterization of building materials from the aqueduct of Antioch-on-the-Orontes (Turkey)

The Roman aqueduct of Antioch-on-the-Orontes (Turkey), a city located near the junction between the active Dead Sea fault and the East Anatolian fault, has been damaged several times due to historical earthquakes, as mentioned in ancient texts. The traces of repairs are studied in order to identify their potential seismic origin. The deformations of the structure were characterised thanks to a LIDAR scan. Several bricks were sampled on different parts of the city’s aqueducts, on the original structure and on repaired parts. The bricks were characterized through a petrological approach. 14C and archaeomagnetism were tested on the bricks in order to constrain the age of their production. The synthesis of all the data showed a local origin for the bricks, and led to the identification of several manufacturing techniques and several types of production, thus, confirming the potentiality of this approach to date and characterise post-seismic repairs.Archeosismicity along the Dead Sea Fault recorded by the Antioche-sur-Orontes aqueduc

Segmentation and Holocene Behavior of the Middle Strand of the North Anatolian Fault (NW Turkey)

International audienceThe North Anatolian Fault (NAF) in the Marmara region is composed of three parallel strands all separated by ∼50 km. The activity of the middle strand, which borders the southern edge of the Marmara Sea, is much debated because of its present-day very low seismicity. This contrasts with historical, archeological and paleoseismological evidence, which suggest several destructive earthquakes have occurred during the last 2000 years. Our study aims to better constrain seismic hazard on the middle strand by exploring its Holocene paleoseismicity. For this, we mapped 148 km of the eastern part of the middle strand, using high-resolution satellite imagery. A series of landforms offset by the middle strand activity have been systematically measured to recover the past ruptures. Three Late Pleistocene-Holocene terraces have been dated with the terrestrial cosmogenic nuclide method, constraining a horizontal slip rate of urn:x-wiley:02787407:media:tect21626:tect21626-math-0001 mm/yr. The statistical analysis of the offsets evidences several major ruptures preserved in the landscape, with coseismic lateral displacements ranging between 3 and 6.5 m. This corresponds to Mw ∼7.3 earthquakes able to propagate along several fault segments. Historical seismicity and paleoseismology data suggest that the last large earthquakes along the middle strand of the NAF (MNAF) happened in 1065 CE and between the 14th and 18th centuries CE. Since then, the MNAF may have accumulated enough stress to generate a destructive rupture

Construction history of the aqueduct of Nicaea (Iznik, NW Turkey) and its on-fault deformation viewed from archaeological and geophysical investigations

International audienceThe aqueduct of Nicaea (modern Iznik, in northwestern Turkey) was studied for the first time using combined stratigraphical and geophysical methods. The analysis of the different materials and building techniques used allowed us to individualize more than forty stratigraphical units on the section investigated, using thirteen specific techniques. The comparison of certain masonries with analogous techniques visible in the defensive walls of the city and our stratigraphical interpretations led us to propose a chronology of the construction divided into nine phases. Some of these rebuildings seem linked to war and earthquake damage. The aqueduct was originally built in the first centuries AD using a framework of terracottas and limestone rubble. Later on, two functional terracotta structures were added and the specus was extensively rebuilt. In a second period, the early facing was replaced by well-cut travertines. Significant rebuilding occurred around the 11 th century when the city went under attacks with the Turks. The last modifications date from the Lascarid period and are probably linked to the construction of a second defensive wall in the 13 th century, which cuts the western end of the aqueduct. Geophysical acquisitions on the eastern section of the aqueduct evidenced a vertical offset of the building located on an active normal fault unsuspected before. This kind of multidisciplinary approaches are powerful tools to study active tectonics and their impact on past societies

Geochemical study of carbonate concretions from the aqueduct of Nîmes (southern France): a climatic record for the first centuries AD?

Abstract The first centuries AD in the Mediterranean region have generally been associated with a warm, stable climate. High-resolution sedimentary archives sensitive to local environmental change are needed to switch from this general frame to the regional scale. Similarly to cave speleothems, laminated carbonate deposits can grow in the channels of aqueducts which transported water from karstic springs during the Roman period. The deposits of the aqueduct of Nîmes (SE France) are exceptional since they may represent several centuries of paleoenvironmental record with a seasonal resolution. δ18O, δ13C and trace elements were measured in three samples from this aqueduct. The comparison of the geochemical signals with the fine texture of the deposits evidenced the seasonal nature of the lamination observed. This allowed us to document the evolution of environment as recorded through the deposit for the period 50–275 AD. The concretions of the aqueduct of Nîmes document rather stable climatic conditions for the first three centuries AD, as well as a local vegetation change possibly linked to an increased in land use

Geochemistry and mineralogy approaches to characterize brick and its lake sediments sources: Antioch Roman City (Southern Turkey)

The Roman aqueduct of Antioch-on-the-Orontes (Southern Turkey) is situated close to the Antioch city. This last is located near the Amik Lake (Lake of Antioch) and close to the junction between the active Dead Sea fault and the East Anatolian fault. During the Roman period, the Amik Plain was more densely occupied than at any time in its history [1]. The study focuses on the bricks and the lake sediments characterization in order to determine the source area as well as the technical production used at this period. For this purpose, several bricks were sampled on different parts of the city's aqueducts. Furthermore, a core of about 6 m of sediments was also collected from the dried Amik Lake. The bricks were characterized through a mineralogical (XRD) and chemical (PIXE-PIGE) approaches. Unfired clay fraction remained as inclusion in the brick was separated and then analysed using XRD. Geochemical composition and clay mineralogy were performed on the raw sediments from the Amik Lake in order to compare the source area. Technological test will be performed on the raw clay sediments from the Amik Lake in the purpose to understand the production techniques used at this time. The age of the brick production was previously dated to the Roman Period [2]. The synthesis of all the data attested the Amik Lake sediment as the raw material for the bricks of the aqueduct. Clay mineral composition from the Roman period deposited in the lake is smectite, illite, kaolinite and small amount of mixed-layer clays. The similar clays composition is found in the remained clays on the brick used for the aqueduct construction. Fast and heterogeneous firing practice characterized the manufacturing of these materials due to the rapid need for the materials during the post-seismic repairs after earthquakes that are mentioned in historical written works. [1] J. Casana, Geomorphology, 101, 429-442 (2008) [2] Y. Benjelloun, J. de Sigoyer, J. Carlut, A. Hubert-Ferrari, H. Dessales, H. Pamir, V. Karabacak, Comptes Rendus Geoscience, 347, 170-180 (2015

Historical Earthquake Scenarios for the Middle Strand of the North Anatolian Fault Deduced from Archeo-Damage Inventory and Building Deformation Modeling

The city of Iznik (ancient Nicaea), located on the middle strand of the North Anatolian fault zone (MNAF), presents outstanding archeological monuments preserved from the Roman and Ottoman periods (first to fifteenth centuries A.D.), bearing deformations that can be linked to past seismic shaking. To constrain the date and intensity of these historical earthquakes, a systematic survey of earthquake archeological effects (EAEs) is carried out on the city's damaged buildings. Each of the 235 EAEs found is given a quality ranking, and the corresponding damage is classified according to the European Macroseismic Scale 1998 (EMS?98). We show that the walls oriented north-south were preferentially damaged, and that most deformations are perpendicular to the walls' axes. The date of postseismic repairs is constrained with available archeological data and new C14 dating of mortar charcoals. Three damage episodes are evidenced: (1) between the sixth and late eighth centuries, (2) between the nineth and late eleventh centuries A.D., and (3) after the late fourteenth century A.D. The repartition of damage as a function of building vulnerability points toward a global intensity VIII on the EMS?98. The 3D modeling of a deformed Roman obelisk shows that only earthquakes rupturing the MNAF can account for this deformation. Their magnitude can be bracketed between Mw 6 and 7. Our archeoseismological study complements the historical seismicity catalog and confirms paleoseismological data, suggesting several destructive earthquakes along the MNAF, since the first century A.D. We suggest the fault might still have accumulated enough stress to generate an Mw 7+ rupture

New Probabilistic Seismic Hazard Model for Nepal Himalayas by Integrating Distributed Seismicity and Major Thrust Faults

Nepal is one of the most seismically active regions in the world, as highlighted by the recent devastating 2015, Mw~7.8 Gorkha earthquake, and a robust assessment of seismic hazard is paramount for the design of earthquake-resistant structures. In this study, we present a new probabilistic seismic hazard assessment (PSHA) for Nepal. We considered data and findings from recent scientific publications, which allowed us to develop a unified magnitude homogenized seismicity catalog and propose alternative seismic source characterization (SSC) models including up-to-date parameters of major thrust faults like main frontal thrust (MFT) and main boundary thrust (MBT), while also considering existing SSC models and various seismic hazard modeling strategies within a logic tree framework. The sensitivity analyses show the seismic hazard levels are generally higher for SSC models integrating the major thrust faults, followed by homogenous volume sources and smoothed seismicity approach. The seismic hazard maps covering the entirety of Nepal are presented as well as the uniform hazard spectra (UHS) for five selected locations (Kathmandu, Pokhara, Biratnagar, Nepalganj, and Dipayal) at return periods of 475- and 2475-years considering Vs,30 = 760 m/s. The results obtained are generally consistent with most recent studies. However, a notable variability in seismic hazard levels and several discrepancies with respect to the Nepal Building Building Code NBC105: 2020 and global hazard model, GEM are noted, and possible causes are discussed