GIS for development: a contradiction in terms?     

Christine E Dunn  Peter J Atkins  Janet G Townsend 《Area》1997,29(2):151-159

Summary Is it possible to make appropriate use of GIS for 'development' (here defined as change desirable for the poor) in countries where human and financial resources may be limited? We argue that it is, and should be taught, but that there are no quick fixes.  相似文献   

Observations of the E-region horizontal winds in the auroral zone and at mid-latitudes by a ground-based interferometer     

Vincent Fauliot  Gérard Thuillier  Michel Hersé 《Annales Geophysicae》1995,13(11):1172-1186

The MICADO instrument, consisting of a Michelson interferometer, has observed winds and temperatures during three winter campaigns in the auroral zone, and during 2 years at the Observatoire de Haute-Provence. The instrument observed the O(¹S) oxygen emission line. Emission from this line originates from both the E- and F-regions. A method to separate the contribution from these two regions is presented for cases when the thermospheric component is comparable to that for the mesosphere. For the auroral latitudes, a mean model of the meridional and zonal neutral wind components as a function of magnetic activity and time is presented and compared to predictions from recent empirical models. For the mid-latitudes, several properties of the semi-diurnal tides are shown and compared to radar observations and predictions from recent theoretical models.  相似文献   

Sliders and tension controlled reinforced elastomeric bearings combined for earthquake isolation     

Michel S. Chalhoub  James M. Kelly 《地震工程与结构动力学》1990,19(3):333-344

Essential requirements from a base isolation system include wind restraint, stability and fail-safe capacity. A new base isolation system that satisfies all three requirements and possesses other advantages was tested on the earthquake simulator at the University of California under the base of a one-fourth scale nine storey steel structure. The base behaves as fixed for low magnitude inputs. When sliding starts the rubber bearings provide additional stiffness and recentering. Displacements are better controlled than the ones for a purely elastomeric isolation system. Vertical deflections due to large horizontal drift encountered in solely rubber systems are eliminated. The fail safe capacity is provided by tension restrainers installed inside the rubber bearings, and by the constant contact of the base with the sliders. Base shear hysteresis loops are drastically enlarged by the presence of the sliders.  相似文献   

Calculated greenschist facies mineral equilibria in the system CaO−FeO−MgO−Al2O3−SiO2−CO2−H2O     

Thomas M. Will  Roger Powell  Tim Holland  Michel Guiraud 《Contributions to Mineralogy and Petrology》1990,104(3):353-368

The kinetic problems associated with the experimental determination of reactions among complex solidsolution phases at low temperatures have hindered our understanding of the phase relations in greenschist facies rocks. In the absence of reliable experimental data, we have used the new, expanded internally-consistent thermodynamic dataset of Holland and Powell (1990), to present calculated phase equilibria for the system CaO–FeO–MgO–Al₂O₃–SiO₂–H₂O–CO₂ (CaFMASCH) with quartz in eccess, in the range 400°–500°C at low to intermediate pressures, involving the minerals amphibole, chlorite, anorthite, clinozoisite, dolomite, chloritoid, garnet, margarite, andalusite, and calcite. By solving independent sets of non-linear equations formed from equilibrium relationships, we calculate not only the loci of reactions in pressuretemperature-x(CO₂) space, but also the compositions of coexisting minerals in terms of the substitutions, FeMg_-1 and (Fe,Mg)SiAl_-1Al_-1. Invariant, univariant and divariant equilibria are calculated and discussed in relation to naturally-occurring greenschist facies metabasic and siliceous dolomitic mineral assemblages. We thus avoid the use of activity-corrected curves so commonly presented in the literature as a substitute for genuine univariant phase diagram boundaries.  相似文献   

A magnetotelluric investigation of the structural geology beneath Charlevoix Crater, Quebec     

Marianne Mareschal  Michel Chouteau 《Physics of the Earth and Planetary Interiors》1990,60(1-4):120-131

The results of ten tensor magnetotelluric soundings recorded within the Charlevoix crater are presented. The geological complexity of the region (the crater is located at the junction of two major geological provinces, i.e. the crystalline basement of the Canadian shield and the more conductive sediments of the Appalachian system) and the amount of cultural noise present in our data prevent a highly definitive interpretation of the shallow structure. A subhorizontal conductive fault related to Rondot's (1971) structural sketch of the original impact structure may exist within the upper 5 km, but it is not completely constrained by the data. Pseudo 3D modelling using stacked thin sheets indicates that superficial patches of high conductivity may explain the large anisotropy observed at the long periods and suggests that our deeper structures fit well with the 2D model previously proposed by Kurtz (1982) for the region.  相似文献   

Direct dating of Plio-Quaternary pumices by Ar/Ar step-heating and single-grain laser fusion methods: the example of the Monts-Dore massif (Massif Central, France)     

Gilbert Fraud  Philippe Lo Bello  Chris M. Hall  Jean-Marie Cantagrel  Derek York  Michel Bernat 《Journal of Volcanology and Geothermal Research》1990,40(1)

K-feldspars separated from Plio-Quaternary pumice flows of the Monts-Dore massif (Massif Central, France) give ⁴⁰Ar/³⁹Ar saddle-shaped age spectra. Laser-probe analysis of hand-picked single grains gives ages in agreement with those of overlying and underlying lava flows previously dated by the conventional K-Ar method. The laser-probe ages are lower than the minimum ages measured on the populations of grains by the step-heating method. As previously suggested by Lo Bello and co-workers for the pumice flow of Neschers belonging to the same volcanic massif, the saddle-shaped age spectra are ascribed to the different Ar-release patterns of two populations of K-feldspars: (1) young sanidine phenocrysts of the pumices; and (2) old K-feldspars plucked from the Hercynian basement during the explosive eruption. Measurements of both the granitic rocks from surrounding areas and the granitic xenoliths included in pumices give ages around 330 Ma and show that most of the xenocrysts included in the pumices did not lose significant amounts of argon during the eruption. With the ⁴⁰Ar/³⁹Ar step-heating method, we were able to detect contamination of Quaternary K-feldspars by Hercynian K-feldspars as low as 0.25. Because pumice flows of the Monts-Dore massif crop out over large areas, these new ages will be useful for establishing a precise stratigraphy of the European Plio-Quaternary.  相似文献   

Flexural response of the oceanic lithosphere at an arc—arc junction: implication for the subduction of aseismic ridges     

Christine Deplus  Jacques Dubois 《Tectonophysics》1989,160(1-4):63-73

The deformation of the oceanic lithosphere subducting at the junction of two trenches is studied by means of a three-dimensional finite-element analysis. Results show that the existence of a junction (i.e. a change in trend of the trench axis) yields a specific shape of the outer topographic rise. In a convex junction area—such as the Japan and Kuril trenches, the topographic bulge presents a “dome”, whereas in a concave junction area—such as the Java and Sumatra trenches, this bulge is less pronounced. These theoretical results are confirmed by the bathymetry seaward of the junctions of the Japan and Kuril trenches and of the Peru-Chile trench. Moreover, the existence of the abnormal topographic dome in front of a convex junction contributes to the creation of normal faults which help the subduction of seamounts or of other bathymetric features in such areas.  相似文献   

Methods of calculating petrophysical properties from lattice preferred orientation data   总被引：13，自引：0，他引：13  

David Mainprice  Michel Humbert 《Surveys in Geophysics》1994,15(5):575-592

We consider the theoretical problems of calculating the physical properties of an aggregate from the constituent crystal properties and the lattice preferred orientation. The notion of a macroscopically homogeneous sample with an internally varing distribution of stress and strain fields is introduced to explain why further efforts have to be made to improve on the physically based Voigt and Reuss bounds. It is shown that the Voigt and Reuss bounds become increasingly separated with inceasing anisotropy, emphasising the need for better methods. The problem of highly anisotropic minerals is illustrated with polycrystals of plagioclase feldspar and biotite. Biotite is used to illustrate the mean velocity, the geometric mean and the self-consistent methods. The self-consistent method, which is generally accepted to give the best estimate, is almost identical to geometric mean recently introduced by Matthies and Humbert (1993) and similar to the arithmetic mean of the Voigt and Reuss bounds (Hill, 1952). The geometric mean has the powerful physical condition that the aggregate mean is equal to the mean of the inverse property (e.g. mean elastic stiffness and compliance). Despite its lack of theoretical justification the Hill average remains a useful estimate.  相似文献   

The earth surface processes and landforms bibliography     

Christine Windass 《地球表面变化过程与地形》1994,19(9):845-847

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Study of the Santa Catarina aquifer system (Mexico Basin) using magnetotelluric soundings     

Michel Chouteau  Stefka Krivochieva  Ramiro Rodriguez Castillo  Tomas Gonzalez Moran  Virginie Jouanne 《Journal of Applied Geophysics》1994,31(1-4)

A tensor magnetotelluric test survey was carried out in the region of Santa Catarina, located in the Chalco sub-basin of the Mexico Basin. The objective was to define the stratification at depth with an emphasis on the geometry of the main aquifer of that region which is partially known from DC resistivity soundings and drilling. High-quality magnetotelluric soundings could be recorded in the immediate vicinity of large urban zones because the sub-surface is very conductive. Interpretation shows that the solid bedrock is located at a depth of at least 800 m to the south and 1300 m to the north; it could, however, be much deeper. Using complementary DC resistivity sounding and well-logging data, three main layers have been defined overlying the bedrock. These layers are, from surface to bottom, an unsaturated zone of sand, volcanic ash and clay about 10 m thick, followed by a very conductive (1.5 ohm·m) 200 m thick layer of sand and ash with intercalated clay, saturated with highly mineralized water, and finally a zone with resistivity increasing gradually to 60 ohm·m. The investigated deep aquifer constitutes most of this third layer. It consists of a sequence of sand, gravel, pyroclastites and mainly fractured basalts. MT resistivity soundings and magnetic transfer functions also indicate that a shallow resistive structure is dipping, from the northwest, into the lacustrine deposits of the basin. This geologic feature is likely to be highly permeable fractured basaltic flows, which provide a channel by which water contaminated by the Santa Catarina landfill may leak into the basin.  相似文献