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571.
572.
573.
Loess deposition in Asia: its initiation and development before and during the Quaternary 总被引:3,自引:0,他引:3
Andrey E. Dodonov Liping Zhou 《《幕》》2008,31(2):222-225
Dust is important in the Earth environment system. However; the role of dust in climate change remains largely unknown. A better understanding of the temporal and spatial variability of the dust accumulation in Asia forms an important step towards establishing the link between dust deposition and climate change. Here, a summary is given for the timing of the onset and expansion of loess deposition in Asia beginning in the early, Miocene. Recent progress on some aspects of loess chronology and palaeoenvironmental reconstruction is also reviewed. 相似文献
574.
Influence of Structural Non-Stationarity of Surface Roughness on Morphological Characterization and Mechanical Deformation of Rock Joints 总被引:2,自引:2,他引:0
N. Fardin 《Rock Mechanics and Rock Engineering》2008,41(2):267-297
Summary Structural non-stationarity of surface roughness affects accurate morphological characterization as well as mechanical behaviour
of rock joints at the laboratory scale using samples with a size below the stationarity threshold. In this paper, the effect
of structural non-stationarity of surface roughness is investigated by studying the scale dependence of surface roughness
and mechanical behaviour of rock joints. The results show that the structural non-stationarity mainly affects the accurate
characterization of the surface roughness of the fracture samples. It also controls the amount and location of the contact
areas during shear tests, which in turn affects the mechanical properties and asperity degradation of the samples. It is concluded
that for accurate determination of the morphological and mechanical properties of rock joints at laboratory and field scales,
samples with size equal to or larger than the stationarity threshold are required.
Author’s address: Nader Fardin, Rock Mechanics Group, Department of Mining Engineering, Faculty of Engineering, University
of Tehran, P.O. Box: 11365/4563, Tehran, Iran 相似文献
575.
576.
S. T. G. Raghukanth 《Natural Hazards》2008,46(1):1-13
In this article, analytical methods have been used to estimate ground motion during the 8 October 2005, Kashmir earthquake.
Peak ground acceleration (PGA) values at several stations in the epicentral region have been estimated by empirical analytical
source mechanism models. As an alternate analysis, PGA estimates have also been obtained using the stochastic finite fault
seismological model. The estimated PGAs are compared with that obtained from damage values. A PGA contour map in the near-source
region is provided. It is found that very near to the epicenter, PGA would have reached more than 1 g. It is demonstrated
that empirical analytical models can be effectively used to estimate ground motion due to rupture of active faults. 相似文献
577.
H. M. Hussein K. M. Abou Elenean I. A. Marzouk A. Peresan I. M. Korrat E. Abu El-Nader G. F. Panza M. N. El-Gabry 《Natural Hazards》2008,47(3):525-546
The aim of the present work is to compile and update a catalogue of the instrumentally recorded earthquakes in Egypt, with
uniform and homogeneous source parameters as required for the analysis of seismicity and seismic hazard assessment. This in
turn requires a detailed analysis and comparison of the properties of different available sources, including the distribution
of events with time, the magnitude completeness, and the scaling relations between different kinds of magnitude reported by
different agencies. The observational data cover the time interval 1900–2004 and an area between 22°–33.5° N and 25°–36° E.
The linear regressions between various magnitude types have been evaluated for different magnitude ranges. Using the best
linear relationship determined for each available pair of magnitudes, as well as those identified between the magnitudes and
the seismic moment, we convert the different magnitude types into moment magnitudes M
W, through a multi-step conversion process. Analysis of the catalogue completeness, based on the M
W thus estimated, allows us to identify two different time intervals with homogeneous properties. The first one (1900–1984)
appears to be complete for M
W ≥ 4.5, while the second one (1985–2004) can be considered complete for magnitudes M
W ≥ 3. 相似文献
578.
This article describes a unique flood hazard, produced by the dramatic expansion of wetlands in Nelson County, located within
the North American Prairie Pothole Region of North Dakota, USA. There has been an unprecedented increase in the number, average
size, and permanence of prairie wetlands, and a significant increase in the size of a closed lake (Stump Lake) due to a decade-long
wet spell that began in 1993 following a prolonged drying trend. Base-line land cover information from the 1992 USGS National
Land Cover Characterization dataset, and a Landsat TM scene acquired 9 July 2001 are used to assess the growth of the closed
lake and wetland pond surface areas, and to analyze the type and area of various land cover classes inundated between 1992
and 2001. The open water profile in Nelson County changed from one marked by relatively comparable coverage of closed lake
and wetland pond areas in 1992, to one in which wetland open water accounted for the vast majority of total open water in
2001. The bulk of the wetland pond area expansion occurred by displacing existing wetland vegetation and agricultural cropland.
Producers responded to the flood hazard by filing Federal Crop Insurance Corporation (FCIC) claims and enrolling cropland
in the Conservation Reserve Program (CRP), a federal land retirement program. Land taken out of agricultural production has
had an enormous impact upon the agricultural sector that forms the economic base of the rural economy. In 2001 the land taken
out of production due to CRP enrollment and preventive planting claims represented nearly 42% of Nelson County’s 205.2 K ha
base agricultural land. The patterns obtained from this detailed study of Nelson County are likely to be the representative
of the more publicized flood disaster occurring within the Devils Lake Basin of North Dakota. 相似文献
579.
Mineralogy and geochemistry of El Dorado epithermal gold deposit, El Sauce district, central-northern Chile 总被引:1,自引:0,他引:1
J. Carrillo-Rosúa S. Morales-Ruano D. Morata A. J. Boyce M. Belmar A. E. Fallick P. Fenoll Hach-Alí 《Mineralogy and Petrology》2008,92(3-4):341-360
Summary The El Dorado Au-Cu deposit is located in an extensive intra-caldera zone of hydrothermal alteration affecting Upper Cretaceous
andesites of the Los Elquinos Formation at La Serena (≈ 29°47′S Lat., 70°43′W Long., Chile). Quartz-sulfide veins of economic potential are hosted by N25W and N20E
fault structures associated with quartz-illite alteration (+supergene kaolinite). The main ore minerals in the deposit are
pyrite, chalcopyrite ± fahlore (As/(As + Sb): 0.06−0.98), with electrum, sphalerite, galena, bournonite-seligmanite (As/(As
+ Sb): 0.21−0.31), marcasite, pyrrhotite being accessory phases. Electrum, with an Ag content between 32 and 37 at.%, occurs
interstitial to pyrite aggregates or along pyrite fractures. Pyrite commonly exhibits chemical zonation with some zones up
to 1.96 at.% As. Electron probe microanalyses of pyrite indicate that As-rich zones do not exhibit detectable Au values. Fluid
inclusion microthermometry shows homogenization temperatures between 130 and 352 °C and salinities between 1.6 and 6.9 wt.%
NaCl eq. Isotope data for quartz, ankerite and phyllosilicates and estimated temperatures show that δ18O and δD for the hydrothermal fluids were between 3 and 10‰ and between −95 and −75‰, respectively. These results suggest
the mineralizing fluids were a mixture of meteoric and magmatic waters. An epithermal intermediate-sulfidation model is proposed
for the formation of the El Dorado deposit.
Author’s present address: J. Carrillo-Rosúa, Dpto. de Didáctica de las Ciencias Experimentales, Universidad de Granada, Campus de Cartuja, 18071, Granada, Spain 相似文献
580.