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排序方式: 共有464条查询结果,搜索用时 15 毫秒
61.
Xavi Gallach Julien Carcaillet Ludovic Ravanel Philip Deline Christophe Ogier Magali Rossi Emmanuel Malet David Garcia-Sellés 《地球表面变化过程与地形》2020,45(13):3071-3091
In the Mont Blanc massif (European Western Alps), rockfalls are one of the main natural hazards for alpinists and infrastructure. Rockfall activity after the Little Ice Age is well documented. An increase in frequency during the last three decades is related to permafrost degradation caused by rising air temperatures. In order to understand whether climate exerts a long-term control on rockfall occurrence, a selection of paleo-rockfall scars was dated in the Glacier du Géant basin [>3200 m above sea level (a.s.l.)] using terrestrial cosmogenic nuclides. Rockfall occurrence was compared to different climatic and glacial proxies. This study presents 55 new samples (including replicates) and 25 previously-published ages from nine sampling sites. In total, 62 dated rockfall events display ages ranging from 0.03 ± 0.02 ka to 88.40 ± 7.60 ka. Holocene ages and their uncertainties were used to perform a Kernel density function into a continuous dataset displaying rockfall probability per 100 years. Results highlight four Holocene periods of enhanced rockfall occurrence: (i) c. 7–5.7 ka, related to the Holocene Warm Periods; (ii) c. 4.5–4 ka, related to the Sub-boreal Warm Period; (iii) c. 2.3–1.6 ka, related to the Roman Warm Period; and (iv) c. 0.9–0.3 ka, related to the Medieval Warm Period and beginning of the Little Ice Age. Laser and photogrammetric three-dimensional (3D) models of the rock walls were produced to reconstruct the detached volumes from the best-preserved rockfall scars (≤0.91 ± 0.12 ka). A structural study was carried out at the scale of the Glacier du Géant basin using aerial photographs, and at the scale of four selected rock walls using the 3D models. Two main vertical and one horizontal fracture sets were identified. They correspond respectively to alpine shear zones and veins opened-up during long-term exhumation of the Mont Blanc massif. Our study confirms that climate primarily controls rockfall occurrence, and that structural settings, coincident at both the massif and the rock wall scales, control the rock-wall shapes as well as the geometry and volume of the rockfall events. © 2020 John Wiley & Sons, Ltd. 相似文献
62.
Lécuyer Christophe Gasquet Dominique Allemand Pascal Martineau François Martinez Isabelle 《International Journal of Earth Sciences》2017,106(8):2855-2872
International Journal of Earth Sciences - Four imbricated mafic to felsic plutons of Variscan age from Morocco have been investigated for their cooling history and geochemical interactions with... 相似文献
63.
Erosion rates and sediment budgets in vineyards at 1-m resolution based on stock unearthing (Burgundy, France) 总被引:1,自引:0,他引:1
Jrme Brenot Amlie Quiquerez Christophe Petit Jean-Pierre Garcia 《Geomorphology》2008,100(3-4):345-355
A new and simple method is developed to efficiently quantify erosion and deposition rates based on stock unearthing measurements. This is applicable to spatial scales ranging from plot to hillslopes, and to time scales ranging from single hydrologic events to centennial scales. The method is applied to a plot area on vineyard hillslopes in Burgundy (Monthélie, France), with measurement of 4328 vine plants. A sediment budget established at the plot scale shows a mean soil lowering of 3.44 ± 1 cm over 20 years, involving a minimal erosion rate of 1.7 ± 0.5 mm yr− 1. Locally, erosion rates can reach up to 8.2 ± 0.5 mm yr− 1.This approach allows the sediment redistribution to be mapped and analyzed at 1-m resolution. It provides novel insights into the characterization of erosion patterns on pluri-decennial scales and into the analysis of spatial distribution of erosion processes on cultivated hillslopes. 相似文献
64.
65.
Bertrand?GuillierEmail author Jean-Luc?Chatelain Hugo?Perfettini El?Hadi?Oubaiche Christophe?Voisin Rabah?Bensalem Djamel?Machane Mustapha?Hellel 《Bulletin of Earthquake Engineering》2016,14(8):2213-2227
Building frequencies (fundamental and higher modes) are a critical parameter especially in the field of structural health monitoring mainly based on the stability of the structural dynamic parameters of individual building (frequencies, damping and modes shape). One of the most used methods to find out these parameters is based on the use on ambient vibration analysis. In this work, we study the fluctuations over a month period of the fundamental frequencies (transverse and longitudinal) of a 3.5-story RC-building made of 2 identical units connected by a structural joint. Time independent building frequencies is a strong assumption; as illustrated by our experiment showing that over an observation period of a month, building frequencies fluctuate of about 3.5 %. A clear correlation is found between the building frequency fluctuations and temperature variations, with a phase-shift interpreted as the characteristic time of heat diffusion within the walls. This allows: (1) determining the thermal diffusivity of the structure, (2) inferring its relative stiffness variations, and (3) showing that its Young modulus varies linearly with temperature. 相似文献
66.
Many seismic loss problems (such as disruption of distributed infrastructure and losses to portfolios of structures) are dependent upon the regional distribution of ground‐motion intensity, rather than intensity at only a single site. Quantifying ground‐motion over a spatially‐distributed region therefore requires information on the correlation between the ground‐motion intensities at different sites during a single event. The focus of the present study is to assess the spatial correlation between ground‐motion spectral accelerations at different periods. Ground motions from eight well‐recorded earthquakes were used to study the spatial correlations. On the basis of obtained empirical correlation estimates, we propose a geostatistics‐based method to formulate a predictive model that is suitable for simulation of spectral accelerations at multiple sites and multiple periods, in the case of crustal earthquakes in active seismic regions. While the calibration of this model and investigation of its implications were somewhat complex, the model itself is very simple to use for making correlation predictions. A user only needs to evaluate a simple equation relying on three sets of coefficients provided here to compute a correlation coefficient for spectral values at two periods and at a specified separation distance. These results may then be used in evaluating the seismic risk of portfolios of structures with differing fundamental periods. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
67.
Hilary McMillan Alberto Montanari Christophe Cudennec Hubert Savenije Heidi Kreibich Tobias Krueger 《水文科学杂志》2013,58(7):1174-1191
ABSTRACTIn 2013, the International Association of Hydrological Sciences (IAHS) launched the hydrological decade 2013–2022 with the theme “Panta Rhei: Change in Hydrology and Society”. The decade recognizes the urgency of hydrological research to understand and predict the interactions of society and water, to support sustainable water resource use under changing climatic and environmental conditions. This paper reports on the first Panta Rhei biennium 2013–2015, providing a comprehensive resource that describes the scope and direction of Panta Rhei. We bring together the knowledge of all the Panta Rhei working groups, to summarize the most pressing research questions and how the hydrological community is progressing towards those goals. We draw out interconnections between different strands of research, and reflect on the need to take a global view on hydrology in the current era of human impacts and environmental change. Finally, we look back to the six driving science questions identified at the outset of Panta Rhei, to quantify progress towards those aims.
Editor D. Koutsoyiannis; Associate editor not assigned 相似文献
68.
Eduard Saura Jean‐Christophe Embry Jaume Vergés David W. Hunt Emilio Casciello Stéphane Homke 《Basin Research》2013,25(2):149-171
The evolution from Late Cretaceous to early Eocene of the well dated Amiran foreland basin in the NW Iranian Zagros Mountains is studied based on the reconstruction of successive thickness, palaeobathymetry and subsidence maps. These maps show the progressive forelandwards migration of the mixed carbonate‐siliciclastic system associated with a decrease in creation of accommodation. Carbonate facies variations across the basin suggest a structural control on the carbonate distribution in the Amiran foreland basin, which has been used as initial constraint to study the control exerted by syndepositional folding in basin architecture and evolution by means of stratigraphic numerical modelling. Modelled results show that shallow bathymetries on top of growing folds enhance carbonate production and basin compartmentalization. As a consequence, coarse clastics become restricted to the internal parts of the basin and only the fine sediments can by‐pass the bathymetric highs generated by folding. Additionally, the development of extensive carbonate platforms on top of the anticlines favours the basinwards migration of the depositional system, which progrades farther with higher fold uplift rates. In this scenario, build‐ups on top of anticlines record its growth and can be used as a dating method. Extrapolation of presented modelling results into the Amiran foreland basin is in agreement with an early folding stage in the SE Lurestan area, between the Khorramabad and Kabir Kuh anticlines. This folding stage would enhance the development of carbonate platforms on top of the anticlines, the south‐westward migration of the system and eventually, the complete filling of the basin north of the Chenareh anticline at the end of the Cuisian. Incremental thickness maps are consistent with a thin (0.4–2 km) ophiolite complex in the source area of the Amiran basin. 相似文献
69.
Rémy Thibaud Géraldine Del Mondo Thierry Garlan Ariane Mascret Christophe Carpentier 《Transactions in GIS》2013,17(5):742-762
Defining a model for the representation and the analysis of spatio‐temporal dynamics remains an open domain in geographical information sciences. In this article we investigate a spatio‐temporal graph‐based model dedicated to managing and extracting sets of geographical entities related in space and time. The approach is based on spatial and temporal local relations between neighboring entities during consecutive times. The model allows us to extract sets of connected entities distant in time and space over long periods and large spaces. From GIS concepts and qualitative reasoning on space and time, we combine the graph model with a dedicated spatial database. It includes information on geometry and geomorphometric parameters, and on spatial and temporal relations. This allows us to extend classical measurements of spatial parameters, with comparisons of entities linked by complex relations in space and time. As a case study, we show how the model suggests an efficient representation of dunes dynamics on a nautical chart for safe navigation. 相似文献
70.
Christophe Béné Louisa Evans David Mills Solomon Ovie Aminu Raji Ahmadu Tafida Amaga Kodio Famory Sinaba Pierre Morand Jacques Lemoalle Neil Andrew 《Global Environmental Change》2011,21(4):1173-1184
Resilience thinking is an important addition to the range of frameworks and approaches that can be used to understand and manage complex social–ecological systems like small-scale fisheries. However, it is yet to lead to better environmental or development outcomes for fisheries stakeholders in terms of food security, improved livelihoods and ecological sustainability. This paper takes an empirical approach by focusing on the fundamentals of resilience thinking to evaluate its usefulness in developing relevant management interventions in small-scale fisheries in the Niger River Basin in West Africa. The paper presents the outputs of a participatory assessment exercise where both fishery communities and local experts were involved at two different scales. The resilience frame used was designed to facilitate the identification of socially defined thresholds that help delineate the desirability of the current system configuration and provides a diagnosis framework that tailors management solutions to problems in local context. The analysis highlights some key contributions from resilience thinking to the challenge of diagnosis in small-scale fisheries management in developing countries, as well as important contributions that emerge from taking a pragmatic and critical approach to its application. 相似文献