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81.
82.
Yucca Mountain, the proposed site for the high-level nuclear waste repository, is located just south of where the present
water table begins a sharp rise in elevation. This large hydraulic gradient is a regional feature that extends for over 100 km.
Yucca Mountain and its vicinity are underlain by faulted and fractured tuffs with hydraulic conductivities controlled by flow
through the fractures. Close to and parallel with the region of large hydraulic gradient, and surrounding the core of the
Timber Mountain Caldera, there is a 10- to 20-km-wide zone containing few faults and thus, most likely, few open fractures.
Consequently, this zone should have a relatively low hydraulic conductivity, and this inference is supported by the available
conductivity measurements in wells near the large hydraulic gradient. Also, slug injection tests indicate significantly higher
pressures for fracture opening in wells located near the large hydraulic gradient compared to the opening pressures in wells
further to the south, hence implying that lower extensional stresses prevail to the north with consequently fewer open fractures
there. Analytical and numerical modeling shows that such a boundary between media of high and low conductivity can produce
the observed, large hydraulic gradient, with the high conductivity medium having a lower elevation than the water table. Further,
as fractures can close due to tectonic activity, the conductivity of the Yucca Mountain tuffs can be reduced to a value near
that for the hydraulic barrier due to strain release by a moderate earthquake. Under these conditions, simulations show that
the elevation of the steady-state water table could rise between 150 and 250 m at the repository site. This elevation rise
is due to the projected shift in the location of the large hydraulic gradient to the south in response to a moderate earthquake,
near magnitude 6, along one of the major normal faults adjacent to Yucca Mountain. As the proposed repository would only be
200–400 m above the present water table, this predicted rise in the water table indicates a potential hazard involving water
intrusion.
Received: 7 June 1996 / Accepted: 19 November 1996 相似文献
83.
84.
AVHRR satellite imagery of the southern Mid-Atlantic Bight during May 1993 revealed a large area of cold water over the shelf break and slope that appeared to spin up into a series of southward propagating anticyclonic eddies. The eddies had diameters of 35–45 km at the surface and moved southward at about 20 cm/sec. A radial TOYO CTD (to 50m) and ADCP velocity (to 400m) transect was conducted across the southern-most of these eddies. The upper 50 meters had minimum temperatures of less than 7°C and salinities of about 33 pss, characteristics similar to cold pool waters usually found over the continental shelf. ADCP velocity data from one of the eddies revealed anticyclonic flow extending to a depth of about 250m. The transport of cold pool water by the eddies was estimated to be 0.1 to 0.2 Sv which is of the same order as the annual mean alongshore transport of shelf water in this region. The origin of the deeper water within the eddy is unlikely to be the continental shelf because the shelf break is less than 100 m. The depth and velocity profiles along the TOYO transect were consistent with the constant potential vorticity eddy model of Flierl (1979) although the source of the eddy kinetic energy is uncertain. The cause for the exodus of cold pool water from the shelf, which extended northward to at least 38°N, is unclear but must involve the establishment of an alongshore baroclinic pressure gradient against the usual southwestward shelf flow. It is possible that the intrusion of Gulf Stream waters onto the shelf near Cape Hatteras was a precursor of this off shelf transport. The southern-most eddy was marked by high biological productivity and very high oxygen supersaturation. The phytoplankton bloom detected within the exported cold pool water, located over the continental slope, suggests a mechanism whereby production fueled by nutrients derived from the shelf can be locally exported into deep water. 相似文献
85.
Twenty-two dark inclusions (DIs) from Allende (18), Leoville (2), Vigarano (1) and Efremovka (1) were studied by the I-Xe method. All except two of these DIs (Vigarano 2226 and Leoville LV2) produce well-defined isochrons, and precise I-Xe ages. The Allende DIs formed a tight group about 1.6 Ma older than Shallowater (4.566 ± 0.002 Ga), about 5 Ma older than four previously studied Allende CAIs. Most of the dark inclusions require trapped Xe with less 129Xe (or more 128Xe) than conventional planetary Xe (well restricted in composition by Q-Xe or OC-Xe). Studies of an irradiated/unirradiated DI pair from Allende demonstrate that the 128Xe/132Xe ratio in trapped is normal planetary, so that a 129Xe/132Xe ratio below planetary seems to be required. Yet, this is not possible given constraints on 129Xe evolution in the early solar system. Trends among all of the Allende DIs suggest that an intimate mixture of partially decayed iodine and Xe formed a pseudo trapped Xe component enriched in both 129Xe and 127I, and subsequently in 128Xe after n-capture during reactor irradiation. Enrichment in radiogenic 129Xe, but with a 129Xe/127I ratio less than that observed in the iodine host phase, places closure of this trapped mixture ≥13 Ma after precipitation of the major iodine-bearing phase. Because the I-Xe isochron is a mixing line between iodine-derived and trapped Xe (pseudo or not), I-Xe ages, given by the slope of this mixing line, are not compromised by the presence of pseudo trapped Xe, and the precision of the I-Xe ages is given by the statistics of the line fit. 相似文献
86.
Environmental geochemistry of Zarshuran Au-As deposit, NW Iran 总被引:2,自引:1,他引:2
Zarshuran deposit is the most famous and important As-Au mine in Iran. However, there is no information on the impact of mining activity on the surrounding environment, especially on water systems. This paper attempts to document the concentration of arsenic and associated elements in waters and sediments resulting from the mining history of Zarshuran, a period covering hundreds of years. Water and sediment samples collected from Zarshuran Stream indicate high content of some potentially toxic elements, especially of As which ranges from 0.028 to 40 ng/l in water and 182 to 36,000 mg/kg in sediment samples. Mining activity, exposure of a large volume of mining wastes to weathering, and the anomalously high background of trace metals in the mining area are considered to be the main sources of heavy metal pollution. 相似文献
87.
88.
The International GPS Service tracking network: Enabling diverse studies and projects through international cooperation 总被引:2,自引:0,他引:2
The International GPS Service (IGS), formulated beginning in 1989 and formalized in 1994, was founded on the collaborative operation of approximately 30 permanent GPS stations to benefit global geodynamics. The same cooperative principles, today applied to a network of over 300 stations, still serve to maximize global benefit without unnecessary duplication of investment in global infrastructure. The scope of applications of the dataset has grown to include atmospheric, oceanographic, subdaily, and low-earth orbiter activities through working groups and pilot projects fostered within the IGS in the now traditional IGS spirit of collaboration. These activities and the IGS infrastructure are viewed as critical elements to the Global Geodetic Observing System. This presentation will review the present nature of the IGS tracking network and its ability to support new applications. 相似文献
89.
E. Cotou A. Gremare F. Charles I. Hatzianestis E. Sklivagou 《Continental Shelf Research》2005,25(19-20):2521
This contribution attempts to determine whether, and to what degree, environmental samples of resuspended particulate matter and sediments exert a toxicological impact. Further, an attempt is made also to screen the toxic level of potentially hazardous sites, based upon established sediment toxicity criteria. Therefore, a rapid, cost-effective and highly sensitive biotest (bioluminescence assay, based upon marine bacteria) has been applied on: biological fluid extracts; bottom sediments; and sediment trap samples. Samples were taken either from the Bay of Banyuls-sur-Mer (northwestern Mediterranean, France) or Thermaikos Gulf (northeastern Mediterranean, Greece). Biological fluid extracts and sediment trap samples corresponded to periods of resuspension events, or preceding and following such events.The results have revealed that the sampling strategy and biotest implemented in this study might be a useful tool for screening the toxicity of resuspended matter and sediments. Resuspension events appear to be able to exert an influence on the chemical forms of the micro-pollutants; thus on their bioavailability and toxicity. Nevertheless, based upon chemical analysis combined with the bioassay, the toxic level of the sediment samples could be determined, with the level at potentially hazardous sites being characterised. 相似文献
90.
Petrology of the Jurassic Shah-Kuh granite (eastern Iran), with reference to tin mineralization 总被引:1,自引:0,他引:1
D. Esmaeily A. Ndlec M.V. Valizadeh F. Moore J. Cotten 《Journal of Asian Earth Sciences》2005,25(6):961-980
The Shah-Kuh granitic pluton of eastern Central Iran was emplaced 165 Ma ago, in an active continental margin setting. It is made of two main units: a granodioritic unit (SiO2=63–71 wt%) to the north–west and a syenogranitic unit (SiO2=73–77 wt%) to the south–east. The former unit displays seriate medium-grained textures and contains locally abundant mafic enclaves. The latter unit is medium- to coarse-grained and porphyritic, with 0.5–3 cm long K-feldspar megacrysts. Fine-grained granitic bodies are present in both units. The rocks are metaluminous to slightly peraluminous (I-type) and peraluminous (S-type) and belong to the ilmenite-series granites. Fractional crystallization appears to have been a very effective differentiation process in both units, and the fractionated mineral assemblages are determined by mass balance calculations. Isotopic data (Sri=0.7065 and εNdt=−2.5) are consistent with a young upper crustal protolith. Tin mineralization in sheeted quartz-tourmaline (-cassiterite) veins is spatially associated with the granodioritic unit. The veins formed by hydraulic fracturing when the granodioritic to monzogranitic magma became water-saturated and exsolved a fluid phase during crystallization. The reduced nature of this magma is responsible for the incompatible behaviour of Sn, likely to favour Sn concentration in the residual melt and then in the exsolved fluid. Another fluid phase was exsolved by the syenogranitic magma and was responsible for local greisenized granites, characterized by high Y and HREE-contents and non-fractionated REE distribution patterns. Field and mineralogical data show that the (B, Sn) vein-forming fluid was different from the (F, Li) greisen-forming fluid. 相似文献