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991.
Landslide susceptibility mapping of the Sera River Basin using logistic regression model 总被引:2,自引:1,他引:1
Nussaïbah B. Raja Ihsan Çiçek Necla Türkoğlu Olgu Aydin Akiyuki Kawasaki 《Natural Hazards》2017,85(3):1323-1346
Of the natural hazards in Turkey, landslides are the second most devastating in terms of socio-economic losses, with the majority of landslides occurring in the Eastern Black Sea Region. The aim of this study is to use a statistical approach to carry out a landslide susceptibility assessment in one area at great risk from landslides: the Sera River Basin located in the Eastern Black Sea Region. This paper applies a multivariate statistical approach in the form of a logistics regression model to explore the probability distribution of future landslides in the region. The model attempts to find the best fitting function to describe the relationship between the dependent variable, here the presence or absence of landslides in a region and a set of independent parameters contributing to the occurrence of landslides. The dependent variable (0 for the absence of landslides and 1 for the presence of landslides) was generated using landslide data retrieved from an existing database and expert opinion. The database has information on a few landslides in the region, but is not extensive or complete, and thus unlike those normally used for research. Slope, angle, relief, the natural drainage network (including distance to rivers and the watershed index) and lithology were used as independent parameters in this study. The effect of each parameter was assessed using the corresponding coefficient in the logistic regression function. The results showed that the natural drainage network plays a significant role in determining landslide occurrence and distribution. Landslide susceptibility was evaluated using a predicted map of probability. Zones with high and medium susceptibility to landslides make up 38.8 % of the study area and are located mostly south of the Sera River Basin and along streams. 相似文献
992.
Grilli Stéphan T. Shelby Mike Kimmoun Olivier Dupont Guillaume Nicolsky Dmitry Ma Gangfeng Kirby James T. Shi Fengyan 《Natural Hazards》2017,86(1):353-391
Natural Hazards - We perform numerical simulations to assess how coastal tsunami hazard from submarine mass failures (SMFs) is affected by slide kinematics and rheology. Two types of two-layer SMF... 相似文献
993.
Paolo S. Garofalo Mattias B. Fricker Detlef Günther Paolo Forti Anna-Maria Mercuri Mara Loreti Bruno Capaccioni 《Earth and Planetary Science Letters》2010,289(3-4):560-569
Three hypogenic caves within the Naica mine of Mexico (Cueva de los Cristales — CLC, Ojo de la Reina — OR, and Cueva de las Velas — CLV) host spectacular gypsum crystals up to 11 m in length. These caves are close to another shallow cave of the area (Cueva de las Espadas — CLE), with which they cover a 160 m-deep vertical section of the local drainage basin. Similar to other hypogenic caves, all these caves lack a direct connection with the land surface and should be unrelated with climate.A record of multi-technique fluid inclusion data and pollen spectra from cave and mine gypsum indicates surprisingly that climatic changes occurring at Naica could have controlled fluid composition in these caves, and hence crystal growth. Microthermometry and LA-ICP-Mass Spectrometry of fluid inclusions indicate that the shallow, chemically peculiar, saline fluid (up to 7.7 eq. wt.%NaCl) of CLE could have formed from evaporation, during a dry and hot climatic period. The fluid of the deep caves was instead of low salinity (~ 3.5 eq. wt.% NaCl) and chemically homogeneous, and was poorly affected by evaporation. We propose that mixing of these two fluids, generated at different depths of the Naica drainage basin, determined the stable supersaturation conditions for the gigantic gypsum crystals to grow. Fluid mixing was controlled by the hydraulic communication between CLE and the other deep caves, and must have taken place during cycles of warm-dry and fresh-wet climatic periods, which are known to have occurred in the region. Pollen grains from a 35 ka-old gypsum crystal of CLC corresponds to a fairly homogenous catchment basin made of a mixed broadleaf wet forest, which suggests precipitation during a fresh-wet climatic period and confirms our interpretation of the fluid inclusion data.The unusual combination of geological and geochemical factors of Naica suggests that other hypogenic caves found elsewhere may not host similar crystals. However, this work shows that fluid inclusions and pollen spectra represent a useful tool for cave studies in general, and if used in future studies might be essential to unravel the mechanisms of hypogenic deposition. 相似文献
994.
995.
Airborne light detection and ranging (LiDAR) bathymetry appears to be a useful technology for bed topography mapping of non‐navigable areas, offering high data density and a high acquisition rate. However, few studies have focused on continental waters, in particular, on very shallow waters (<2 m) where it is difficult to extract the surface and bottom positions that are typically mixed in the green LiDAR signal. This paper proposes two new processing methods for depth extraction based on the use of different LiDAR signals [green, near‐infrared (NIR), Raman] of the SHOALS‐1000T sensor. They have been tested on a very shallow coastal area (Golfe du Morbihan, France) as an analogy to very shallow rivers. The first method is based on a combination of mathematical and heuristic methods using the green and the NIR LiDAR signals to cross validate the information delivered by each signal. The second method extracts water depths from the Raman signal using statistical methods such as principal components analysis (PCA) and classification and regression tree (CART) analysis. The obtained results are then compared to the reference depths, and the performances of the different methods, as well as their advantages/disadvantages are evaluated. The green/NIR method supplies 42% more points compared to the operator process, with an equivalent mean error (?4·2 cm verusu ?4·5 cm) and a smaller standard deviation (25·3 cm verusu 33·5 cm). The Raman processing method provides very scattered results (standard deviation of 40·3 cm) with the lowest mean error (?3·1 cm) and 40% more points. The minimum detectable depth is also improved by the two presented methods, being around 1 m for the green/NIR approach and 0·5 m for the statistical approach, compared to 1·5 m for the data processed by the operator. Despite its ability to measure other parameters like water temperature, the Raman method needed a large amount of reference data to provide reliable depth measurements, as opposed to the green/NIR method. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
996.
Rock slope instability assessment using spatially distributed structural orientation data in Darjeeling Himalaya (India) 总被引:1,自引:0,他引:1
Saibal Ghosh Andreas Günther Emmanuel John M. Carranza Cees J. van Westen Victor G. Jetten 《地球表面变化过程与地形》2010,35(15):1773-1792
We discuss a geographic information system (GIS)‐based methodology for rock slope instability assessment based on geometrical relationships between topographic slopes and structural discontinuities in rocks. The methodology involves (a) regionalization of point observations of orientations (azimuth and dip) of structural discontinuities in rocks in order to generate a digital structural model (DStM), (b) testing the kinematical possibility of specific modes of rock slope failures by integrating DStMs and digital elevation model (DEM)‐derived slope and aspect data and (c) computation of stability scenarios with respect to identified rock slope failure modes. We tested the methodology in an area of 90 km2 in Darjeeling Himalaya (India) and in a small portion (9 km2) within this area with higher density of field structural orientation data. The results of the study show better classification of rock slope instability in the smaller area with respect to known occurrences of deep‐seated rockslides than with respect to shallow translational rockslides, implying that structural control is more important for deep‐seated rockslides than for shallow translational rockslides. Results of scenario‐based analysis show that, in rock slopes classified to be unstable, stress‐induced rock slope instability tends to increase with increasing level of water saturation. The study demonstrates the usefulness of spatially distributed data of orientations of structural discontinuities in rocks for medium‐ to small‐scale classification of rock slope instability in mountainous terrains. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
997.
998.
Olivier Merle Stéphanie Barde-Cabusson Benjamin van Wyk de Vries 《Bulletin of Volcanology》2010,72(2):131-147
The standard model of caldera formation is related to the emptying of a magma chamber and ensuing roof collapse during large
eruptions or subsurface withdrawal. Although this model works well for numerous volcanoes, it is inappropriate for many basaltic
volcanoes (with the notable exception of Hawaii), as these have eruptions that involve volumes of magma that are small compared
to the collapse. Many arc volcanoes also have similar oversized depressions, such as Poas (Costa Rica) and Aoba (Vanuatu).
In this article, we propose an alternative caldera model based on deep hydrothermal alteration of volcanic rocks in the central
part of the edifice. Under certain conditions, the clay-rich altered and pressurized core may flow under its own weight, spread
laterally, and trigger very large caldera-like collapse. Several specific mechanisms can generate the formation of such hydrothermal
calderas. Among them, we identify two principal modes: mode 1: ripening with summit loading and flank spreading and mode II:
unbuttressing with flank subsidence and flank sliding. Processes such as summit loading or flank subsidence may act simultaneously
in hybrid mechanisms. Natural examples are shown to illustrate the different modes of formation. For ripening, we give Aoba
(Vanuatu) as an example of probable summit loading, while Casita (Nicaragua) is the type example of flank spreading. For unbuttressing,
Nuku Hiva Island (Marquesas) is our example for flank subsidence and Piton de la Fournaise (La Réunion) is our example of
flank sliding. The whole process is slow and probably needs (a) at least a few tens of thousands of years to deeply alter
the edifice and reach conditions suitable for ductile flow and (b) a few hundred years to achieve the caldera collapse. The
size and the shape of the caldera strictly mimic that of the underlying weak core. Thus, the size of the caldera is not controlled
by the dimensions of the underlying magma reservoir. A collapsing hydrothermal caldera could generate significant phreatic
activity and trigger major eruptions from a coexisting magmatic complex. As the buildup to collapse is slow, such caldera-forming
events could be detected long before their onset. 相似文献
999.
Tanja R. Müller 《Singapore journal of tropical geography》2010,31(3):330-342
This article summarizes findings from a research project on junior farmer field and life schools (JFFLS) as an agriculture‐based intervention to improve the livelihood prospects of children and orphans made vulnerable by HIV/AIDS in central Mozambique. In the sites investigated JFFLS have opened up concrete present and potential livelihood options in agriculture and beyond. More generally, the resource profile dynamics of participants are altered in ways that provide strong grounds to believe that the skills and knowledge they have gained will positively impact the trajectories of their future lives. In terms of HIV/AIDS mitigation, the findings recommend livelihood‐based interventions aimed at altering the vulnerability context of specific population groups. 相似文献
1000.
Stéphane Couturier Jean‐François Mas Erna López‐Granados Jorge Benítez Valdemar Coria‐Tapia Álvaro Vega‐Guzmán 《Singapore journal of tropical geography》2010,31(2):163-179
The accuracy of the Mexican National Forest Inventory (NFI) map is derived in four distinct ecogeographical areas, using an assessment design tailored for the project. A main achievement of the design was to integrate the high diversity of classes encompassed at the most detailed subcommunity level of the classification scheme within a cost‐controlled statistically sound assessment. A hybrid double sampling strategy was applied to the 2.5 million‐ha study area. A total of 5955 reference sites were verified against their NFI map label. The availability of detailed quasi‐synchronous reference data for the 2000 Landsat‐derived NFI and the high diversity of mapped classes allowed a careful thematic analysis on the selected regions, relevant for national extrapolation. Global accuracy estimates of 64–78 per cent were registered among the four ecogeographical areas (two with mainly temperate climate and the other two with mainly tropical climate), with the lower accuracy levels found in areas more densely covered with forests. According to the estimates, the NFI map tends to underestimate the presence of temperate forest (especially oak) and overestimate the presence of tropical forest in the areas investigated. The analysis of confusions reveals difficulties in unambiguously interpreting or labelling forests with secondary vegetation, herbaceous and/or shrub‐like vegetation as well as distinguishing between aquatic vegetation types. The design proved useful from the perspective of accuracy assessments of regional maps in biodiverse regions. 相似文献