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401.
G. N. Sadovnikov 《Stratigraphy and Geological Correlation》2008,16(1):31-46
A unique succession of volcanogenic deposits with representative paleontological remains characterizing the Permian-Triassic boundary interval in the North Siberian platform and Taimyr is described. The succession is suitable for selecting a standard for the Triassic base in nonmarine deposits. Abundant and diverse fossils occurring in the succession evidence that volcanism responsible for origin of the plateau basalt province in Siberia was not a brief epoch of paroxysmal eruptions, which eliminated everything alive. Throughout the formation history of relevant plateau basalts, the organic world of the plateau and around existed and gradually evolved. 相似文献
402.
403.
Quantitative sinkhole hazard assessments in karst areas allow calculation of the potential sinkhole risk and the performance
of cost-benefit analyses. These estimations are of practical interest for planning, engineering, and insurance purposes. The
sinkhole hazard assessments should include two components: the probability of occurrence of sinkholes (sinkholes/km2 year) and the severity of the sinkholes, which mainly refers to the subsidence mechanisms (progressive passive bending or
catastrophic collapse) and the size of the sinkholes at the time of formation; a critical engineering design parameter. This
requires the compilation of an exhaustive database on recent sinkholes, including information on the: (1) location, (2) chronology
(precise date or age range), (3) size, and (4) subsidence mechanisms and rate. This work presents a hazard assessment from
an alluvial evaporite karst area (0.81 km2) located in the periphery of the city of Zaragoza (Ebro River valley, NE Spain). Five sinkholes and four locations with features
attributable to karstic subsidence where identified in an initial investigation phase providing a preliminary probability
of occurrence of 0.14 sinkholes/km2 year (11.34% in annual probability). A trenching program conducted in a subsequent investigation phase allowed us to rule
out the four probable sinkholes, reducing the probability of occurrence to 0.079 sinkholes/km2 year (6.4% in annual probability). The information on the severity indicates that collapse sinkholes 10–15 m in diameter
may occur in the area. A detailed study of the deposits and deformational structures exposed by trenching in one of the sinkholes
allowed us to infer a modern collapse sinkhole approximately 12 m in diameter and with a vertical throw of 8 m. This collapse
structure is superimposed on a subsidence sinkhole around 80 m across that records at least 1.7 m of synsedimentary subsidence.
Trenching, in combination with dating techniques, is proposed as a useful methodology to elucidate the origin of depressions
with uncertain diagnosis and to gather practical information with predictive utility about particular sinkholes in alluvial
karst settings: precise location, subsidence mechanisms and magnitude, and timing and rate of the subsidence episodes. 相似文献
404.
Gregory P. Marchildon Suren Kulshreshtha Elaine Wheaton Dave Sauchyn 《Natural Hazards》2008,45(3):391-411
Agriculture in the southern Great Plains of Canada has been particularly vulnerable to prolonged episodes of drought. Using
climate data and a precipitation minus potential evapotranspiration index, the extent of the region’s exposure to drought
is examined. Between 1914 and 1917, the Dry Belt was particularly vulnerable to drought, whereas after 1928, a much larger
region known as the Palliser Triangle covering most of southern Alberta and Saskatchewan was much more exposed to drought.
These droughts provoked major institutional adaptation, in particular the establishment of the Special Areas Board by the
Government of Alberta, and the creation of the Prairie Farm Rehabilitation Administration by the Government of Canada. Both
organizations have proved to be relatively permanent public adaptations to the natural hazard of drought in the region. Moreover,
these earlier experiences with prolonged drought as well as institution-building may be of value in helping the residents
of the Palliser Triangle adapt to predicted climate changes in the future as well as anticipate some of the barriers to effective
institutional adaptation. 相似文献
405.
In this study, households’ decisions on reconstruction of damaged houses were modeled, using questionnaire data in Japan.
Characteristics of households’ decisions were investigated using parameter estimation results. The effects of subsidizing
policy were evaluated as follows. First, subsidy for rebuilding may be effective for the households whose houses were heavily
damaged. Second, there is a possibility that subsidy accelerated rebuilding of houses by the households having children. Third,
subsidy for rebuilding may not be effective for elderly people’s households and households in depopulated areas. 相似文献
406.
Tidal inundation mapping under enhanced land subsidence in Semarang,Central Java Indonesia 总被引:3,自引:0,他引:3
Tidal inundation by high tide under enhanced land subsidence is a damaging phenomenon and a major threat to the Semarang urban
area in Indonesia. It impacts on economic activities, as well as the cost of an emergency program and causes interruption
of pubic services, danger of infectious diseases and injury to human lives. This study examines a spatial analysis tool on
the GIS-raster system for the tidal inundation mapping based on the subsidence-benchmark data and modified detail digital
elevation model. Neighborhood operation and iteration model as a spatial analysis tool have been applied in order to calculate
the encroachment of the tidal inundation on the coastal area. The resulting map shows that the tidal flood spreads to the
lowland area and causes the inundation of coastal settlement, infrastructure, as well as productive agricultural land, i.e.,
the fish-pond area. The monitoring of the vulnerable area due to the tidal inundation under the scenario of extended land
subsidence plays an important role in long-term coastal zone management in Semarang. 相似文献
407.
Prakash C. Sinha Indu Jain Neetu Bhardwaj Ambarukhana D. Rao Shishir K. Dube 《Natural Hazards》2008,45(3):413-427
The Orissa coast of India is one of the most vulnerable regions of extreme sea levels associated with severe tropical cyclones.
There was extensive loss of life and property due to the October 1999 super cyclone, which devastated large part of the Orissa
coast. The shallow nature of the head bay, presence of a large number of deltas formed by major rivers of Orissa such as Mahanadi
and Dhamra, and high tidal range are responsible for storm surge flooding in the region. Specifically, rising and falling
tidal phases influence the height, duration, and arrival time of peak surge along the coast. The objective of the present
study is to evaluate the tide-surge interaction during the 1999 Orissa cyclone by using nonlinear vertically integrated numerical
models. The pure tidal solution for the head bay region of the Bay of Bengal provides the initial condition for the fine resolution
nested grid Orissa model. However, the feedback from the Orissa model does not affect the head bay model as the study provides
a one-way interaction. Numerical experiments are performed to study the tide-surge interaction by considering various relative
phases of the tidal waves with the surge-wave produced by 1999 Orissa cyclone. The comparison, although utilizing only the
limited estimates of tidal data, appears adequate to assert that the principal features are reproduced correctly. 相似文献
408.
409.
苏北盘石山、练山地幔捕虏体的PGE地球化学 总被引:3,自引:0,他引:3
通过锍镍火试金预富集法,分析了位于郯庐断裂带东侧的盘石山、练山地幔橄榄岩包体中铂族元素(PGE)和Au含量.不同于部分熔融残留成因地幔橄榄岩中通常所观察到的负斜率型或平坦型的分布模式,这两地的地幔橄榄岩以Pt、Pd、Ru相对富集,Ir、Rh相对亏损的"燕子型"分布模式为特征.Pt、Pd等不相容元素富集说明上地幔除经历过早期的部分熔融外,还经历了后期富Pt、Pd的高熔/岩比的熔(流)体的层析分离交代作用影响.盘石山地幔橄榄岩的PGE总量比练山高,Os的含量也比原始地幔值高;而练山地幔橄榄岩的Os含量比原始地幔值低,说明交代作用带走了练山地幔橄榄岩中的Os,却没有很大改变盘石山地幔橄榄岩中的Os含量,这可能与交代熔(流)体含硫量饱和程度有关.Rh的负异常可能与部分熔融过程中熔体较低的fo2有关. 相似文献
410.
Mihoko Hoshino Mitsuyoshi Kimata Norimasa Nishida Masahiro Shimizu 《Physics and Chemistry of Minerals》2008,35(2):59-70
Dissakisites from Trimouns dolomite mine, France, have two kinds of single crystals: chemical-zoned and homogeneous types.
Back-scattered electron microprobe (BSE) images of these dissakisites reveal both Ca–Al rich dark zones and Fe-ΣREE rich bright
zones. Crystal structures of three dark and two bright zones in a chemical-zoned dissakisite and of a homogeneous zone in
unzoned dissakisite were refined to individual R indices (about 3.0–5.0%) based on 1,400 observed [|F
0| > 4σF
0] reflections measured with MoKα X-radiation using the single crystal diffractometer. The differences in brightness between
their BSE images arise from those in coupled substitutions of the elements occupying A2 and M3 sites. The main reason for
these differences is that ten-coordinated A2 polyhedra and M3 octahedra are directly linked through their shared edge, which
creates a great potential for making this coupled substitution. This zoning indicates that formation of the whole zoned crystal,
where each zone could be grown steadily with its crystallographic axes mutually parallel to each other, may be identified
as autoepitaxy. 相似文献