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901.
Elisabeth Pereira François Rouzaud Michelle Salotti Jean-Noël Dubois Jean Ferrandini Marie-Madeleine Ottaviani-Spella 《Geodinamica Acta》2013,26(6):371-375
AbstractSix cavities have been discovered in the Oletta massif. The massif, today constitued of Schistes lustrés with several metres of calcareous layers above them, has undergone intense fracturing. The networks of cavities are organised along north-south and subequatorial directions, and form a narrow bayonnet-network. All the elements in the galleries appear to be karstic: stalagmites, stalactites and calcitic deposits along the walls; but no trace of dissolution or excavation was found. Thus, the origin of the galleries is only tectonic, while the calcitic deposits result from the dissolution of the old, thick calcareous layers above, which are no longer present. The thickness and the volume of the calcitic deposits, which is variable depending on the galleries, indicates the chronology of the different tectonic periods which have fractured the massif. Five tectonic and successsive events have been detected. Calcitic datings confirm the timing of successional fracturing, indicating also the variable age of the fossiliferous Middle Pleistocene deposits found in these cavities. © 1999 Éditions scientifiques et médicales Elsevier SAS 相似文献
902.
Jean Marcoux Jacques Girardeau Eric Fourcade Jean-Paul Bassoullet Jean Philip Michel Jaffrezo 《Geodinamica Acta》2013,26(4-5):313-325
Abstract— The Lhasa Block (s.l.) is bounded to the South by the Tertiary Yarlung Zangbo suture zone and to the North by the terminal Jurassic/earliest Cretaceous Bangong Nu Jiang suture zone. Several tectonostratigraphic units have been recognized in the central-northern part of the Lhasa Block. These are from bottom to top : 1) a thick turbiditic series with a few lenses of allodapic limestones which have yielded an Aalenian — Bajocian foraminiferal assemblage. This series is tectonieally overlain by the Donqiao ophiolite; 2) the continental to shallow marine late Malm to lowermost Cretaceous Zigetang Formation which disconformably overlies the Donqiao ophiolite and 3) continental red detrital rocks or marine Early/Late Aptian boundary to Early Albian foraminifera-rich bedded limestones in which some volcanic rocks are locally interbedded.We discuss the palaeogeographical distribution and biostratigraphical meaning of some foraminifera (Gutnicella cayeuxi (LUCAS), Palorbitolina fen<ícu/o?(Bl .LMKNBACIl), Praeorbitolina cormyi SCHROEDER and Palor-bilolmoides hedini CHREREHI and ScilKOKDK.lt) and their bearing on the radiometric age of the Aptian-Albian boundary. 相似文献
903.
Résumé Dans les régions semi-arides et arides, caractérisées par des précipitations relativement faibles et souvent à caractère torrentiel, les facteurs climatiques jouent un rôle primordial dans l'érosion des sols à l'échelle des versants. La majeure partie de l'exportation des matériaux solides est effectuée par les cours d'eau lors des crues. La présente étude traite de l'évaluation et de la quantification du transport solide dans le bassin versant de l'Oued El Hammam, un sous-bassin important de la Macta caractérisé par une forte érosion hydrique. La sensibilité des roches à l'érosion, l'intensité des précipitations et les perturbations du régime d'écoulement font que le flux des matières en suspension (MES) transportées par l'Oued El Hammam atteint des valeurs très importantes. L'analyse du bilan qui règle le processus pluie–ruissellement–transport solide montre de bonnes relations, notamment entre la lame d'eau écoulée et la quantité de charge solide transportée. Nous présentons des modèles statistiques permettant de reproduire les flux de MES. Après calage et validation des modèles sur les chroniques mesurées, ils sont utilisés afin de reconstituer des chroniques de flux de MES non mesurées, à partir de données historiques de débit et de pluie. L'étude de la relation C–Q à l'échelle de la crue a été modélisée par une fonction puissance Y = aXb ; une analyse statistique de la constante a et de l'exposant b a été menée afin d'expliquer le comportement de ces deux paramètres et de mieux comprendre l'aspect aussi bien pratique que théorique des processus. Citation El Mahi, A., Meddi, M., et Bravard, J.-P., 2012. Analyse du transport solide en suspension dans le bassin versant de l'Oued El Hammam (Algérie du Nord). Hydrological Sciences Journal, 57 (8), 1642–1661. 相似文献
904.
Twin Tsunamis Triggered by the 12 January 2010 Haiti Earthquake 总被引:2,自引:0,他引:2
Hermann M. Fritz Jean Vilmond Hillaire Emanuel Molière Yong Wei Fahad Mohammed 《Pure and Applied Geophysics》2013,170(9-10):1463-1474
On 12 January 2010, a magnitude M w 7.0 earthquake occurred 25 km west–southwest of Haiti’s capital Port-au-Prince causing an estimated 316,000 fatalities, thereby exceeding any previous loss of life from a similar size earthquake. In addition, tsunami waves triggered by the earthquake caused at least three fatalities at Petit Paradis due to a complete lack of tsunami awareness. The International Tsunami Survey Team (ITST) was deployed within weeks of the event and covered the greater Bay of Port-au-Prince and more than 100 km of Hispaniola’s southern coastline. The collected survey data include more than 21 tsunami heights along with observations of coastal land level change. Maximum tsunami heights of 3 m have been measured for two independently triggered tsunamis. 相似文献
905.
906.
This paper discusses the development and implementation of a method that can be used with multi-decadal Landsat data for computing general coastal US land use and land cover (LULC) maps consisting of seven classes. With Mobile Bay, Alabama as the study region, the method that was applied to derive LULC products for nine dates across a 34-year time span. Classifications were computed and refined using decision rules in conjunction with unsupervised classification of Landsat data and Coastal Change and Analysis Program value-added products. Each classification’s overall accuracy was assessed by comparing stratified random locations to available high spatial resolution satellite and aerial imagery, field survey data and raw Landsat RGBs. Overall classification accuracies ranged from 83 to 91% with overall κ statistics ranging from 0.78 to 0.89. Accurate classifications were computed for all nine dates, yielding effective results regardless of season and Landsat sensor. This classification method provided useful map inputs for computing LULC change products. 相似文献
907.
Jean Alberto Mensa Zulema Garraffo Annalisa Griffa Tamay Mehmet Özgökmen Angelique Haza Milena Veneziani 《Ocean Dynamics》2013,63(8):923-941
Frontogenesis and frontal instabilities in the mixed layer are known to be important processes in the formation of submesoscale features. We study the seasonality of such processes in the Gulf Stream (GS) region. To approach this problem, a realistic simulation with the Hybrid Coordinate Ocean Model is integrated for 18 months at two horizontal resolutions: a high-resolution (1/48°) simulation able to resolve part of the submesoscale regime and the full range of mesoscale dynamics, and a coarser resolution (1/12°) case, in which submesoscales are not resolved. Results provide an insight into submesoscale dynamics in the complex GS region. A clear seasonal cycle is observed, with submesoscale features mostly present during winter. The submesoscale field is quantitatively characterized in terms of deviation from geostrophy and 2D dynamics. The limiting and controlling factor in the occurrence of submesoscales appears to be the depth of the mixed layer, which controls the reservoir of available potential energy available at the mesoscale fronts that are present most of the year. Atmospheric forcings are the main energy source behind submesoscale formation, but mostly indirectly through mixed layer deepening. The mixed layer instability scaling suggested in the (Fox-Kemper et al., J Phys Oceanogr 38:1145–1165, 2008) parametrization appears to hold, indicating that the parametrization is appropriate even in this complex and mesoscale dominated area. 相似文献
908.
Gebeyehu Taye Jean Poesen Bas Van Wesemael Matthias Vanmaercke Daniel Teka Jozef Deckers 《自然地理学》2013,34(3):236-259
April lightning production in Richmond County, Georgia, from 1995 to 2003 is considered with regard to the associated risk to golfers and spectators at the Master's Golf Tournament and courses throughout the county. An examination of the April lightning climatology of Georgia, focusing on Richmond County, reveals a minimum in lightning activity during the time of the tournament (the first full week of April). A discriminant analysis of Richmond County lightning production utilizes several meteorological variables in order to discern between three categories of April lightning days: little or no lightning activity, minimal lightning activity, and high lightning activity. The analysis distinguishes relatively well between the categories with only 13.5% of the events misclassified. A composite regional analysis of the three lightning categories illustrates the environmental differences between these events. Although the little or no lightning and high lightning categories are somewhat similar environmentally, the intensity of features separates these events and allows for interpretation. The statistical and synoptic analyses together emphasize the importance of low-level instability and frontal proximity and intensity in enhancing lightning production in thunderstorms during April in and surrounding Richmond County. A multitude of meteorological conditions can lead to thunderstorm development. Localized studies of these environments, especially during times of major outdoor sporting events, are needed to help mitigate the risk associated with lightning. 相似文献
909.
Abstract– Major and trace element abundances were determined on powders prepared from four distinct chips from Allan Hills (ALH) 84001 to constrain the bulk rock composition, and to assess the trace element abundances of orthopyroxenes and phosphates. Our new determinations were used to evaluate the composition of the parental melt of this stone. An unrealistic light rare earth element (REE)‐enriched parental melt is calculated from the composition of the orthopyroxene and relevant equilibrium partition coefficients. The involvement of a small amount of trapped melt and subsolidus reequilibrations between orthopyroxene and the interstitial phases can account for this discrepancy. A parental melt that displays a trace element pattern (REE, Zr, and Hf) that closely resembles enriched shergottites such as Zagami or Los Angeles is calculated if these effects are taken into account. These results suggest that some shergottitic melts were already erupted on Mars during the Noachian. 相似文献
910.
A complete and accurate simulation of two‐phase flow in porous media requires knowledge of all the controlling physics (and values of physical parameters) that play a relevant role and an understanding of the effects of each one on the solution. Of particular concern here is the effect of capillary pressure and the length scale over which it is relevant. The goal of this paper is to provide guidance onto when to include the effects of capillary pressure in the model, and onto what are the resulting length scale restrictions if those effects are to be included. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献