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971.
The populated and expanding city of Chandigarh is located in the foothills of Himalaya, near the potentially active Main Frontal
Thrust (MFT). A hazard assessment for this city is consequently of major importance. Thick sediments underlies the city and
that can potentially amplify the earthquake shaking and contribute to an earthquake disaster in the city. The present study
applies the Horizontal to Vertical Spectral Ratio (HVSR) ambient noise methodology to estimate the resonance frequency of
the soft sediments and to obtain a first order estimate of sediment thickness.
The study indicates that the soil thickness range from 30 to 270 m and that the resonance frequencies vary from 0.236 to 1.479
Hz. A smooth correlation function between soil thickness and resonance frequency is found, indicating relatively homogeneous
soil. 相似文献
972.
Hsien-Tang Tsai Cheng-Jui Tseng Shian-Yang Tzeng Tung-Ju Wu Jen-der Day 《Natural Hazards》2012,62(1):83-91
Typhoon Morakot hit Taiwan in 2009, severely damaging the Alishan National Forest Recreation Area, a famous tourist resort
in Taiwan. The only highway to this area was under repair for 10 months after the typhoon. Consequently, Alishan’s tourism
industry suffered losses estimated at NT$1 billion. This work investigates the impacts of natural hazards on Taiwan’s tourism
industry. First, government, university, and industry experts were invited to a focus-group interview to update criteria for
tourism development in Taiwan. Next, the Analytic Hierarchy Process (AHP) was applied to rank the proposed criteria. Last,
two tourist attractions, one urban and one rural, are discussed in detail. This work proposes three novel dimensions for Taiwan’s
tourism development—destination attraction, destination arrangement, and contingency planning for natural hazards—which comprise
nine criteria. Analytical results will provide Taiwan’s tourism industry with references for future policy-making and sustainable
development. 相似文献
973.
The occurrences of 5772 microwave bursts recorded by the Sagamore Hill and Manilla Solar Radio Observatories over the period January 1968 to July 1970, covering the maximum phase of the current solar cycle at frequencies 2695, 4995 and 8800 MHz and their energy excesses have been examined in relation to the S-component of solar radio emission. The average slowly varying component has been determined by the superposed epoch method commonly known as the Chree analysis. Similar treatment of the bursts, data, mentioned above has been made to examine any probable 27-day variation and the results obtained have been compared with that of the S-component. Further, spectra of the microwave bursts under the so-called spectral type - inverted U, particularly those having a peak at 4995 MHz, have also been examined and compared with the average spectrum of the S-component. Some of the important results obtained from the present analysis are: (1) the nature of variation of both the average number of occurrences and energy excesses of the microwave bursts follow in general the average 27-day variation of the S-component, (2) the number of occurrences and energy excesses of the microwave bursts are comparatively greater in the ascending phase of the 27-day cycle than those in the descending phase, (3) bursts at progressively higher frequencies originate at lower levels in the solar atmosphere than those of the associated S-component, and (4) the average spectrum of the microwave bursts of inverted U spectral type having a peak at 4995 MHz is quite identical in nature to that of the S-component. 相似文献
974.
To investigate an mechanism of the seasonal variation of transport through the Tokara Strait, two numerical experiments with real geometry and wind forcing were carried out. The models are linear barotropic models which are a North Pacific Ocean model and a limited-area model with a fine grid. The seasonal variation of volume transport with a maximum in the summer and a minimum in the autumn could be well reproduced by both models. The results demonstrate the wind stress component normal to a gradient vector of bottom topography is crucial for determining the seasonal variation. The similar seasonal variation widely covers the East China Sea and has a large amplitude near the Tokara Strait. Finally, it can be concluded that winds north of 35°N have little influence on the seasonal response of our model at the Tokara Strait. 相似文献
975.
976.
John Longhi 《Geochimica et cosmochimica acta》2005,69(3):529-539
Graphical analysis of free-energy relationships involving binary quadruple points and their associated univariant equilibria in the system CO2-H2O suggests the presence of at least 2 previously unrecognized quadruple points and a degenerate binary invariant point involving an azeotrope between CO2-rich gas and liquid. Thermodynamic data extracted from the equilibrium involving clathrate (hydrate), gas, and ice (H = G+I) are employed along with published data to calculate the P-T range of the 3-ice equilibrium curve, S+I = H, where S is solid CO2. This equilibrium curve intersects the H = G+I curve approximately where the latter curve intersects the S+H = G curve, thus confirming the existence of one of the inferred quadruple points involving the phases S, G, H, and I. Recognition of some binary equilibria probably have been hampered by extremely low mutual solubilities of CO2 and H2O in the fluids phases which, for example, render the S+H = G virtually indistinguishable from the CO2-sublimation curve.To make the published portion of the L(liquid CO2)-G-H equilibrium “connect” with the other new quadruple point involving S, L, G, and H, it is necessary to change the sense of the equilibrium from L = G+H at higher pressures to L+H = G at lower pressures by positing a L = G azeotrope at very low concentrations of H2O. At the low-pressure origin of the azeotrope, which is only a few bars above the CO2-triple point, the azeotrope curve intersects the 3-phase curve tangentially, creating a degenerate invariant point at which the 3-phase equilibrium changes from L+H = G at lower pressures to L = G+H at higher pressures. The azeotrope curve is offset at slightly lower temperature from the L = G+H curve until the 3-phase equilibrium terminates at the quadruple point involving G, L, H, and W (water). With further increase in pressure the azeotrope curve tracks the L = G+W equilibrium and apparently terminates at a critical end point in close proximity to critical endpoints for the CO2-saturation curve and the L = G+W curve.Thermodynamic data for clathrate extracted from the slope of the H = G+I curve are consistent with a solid-state phase transformation in CO2-clathrate between 235 and 255 K. Published work shows that the type-I clathrate phase, whose atomic structure is a framework of water molecules with CO2 molecules situated in large “guest” sites within the framework, is variable in composition with ∼1 guest site vacancy per unit cell at the high-temperature limit of its stability; the number of water molecules, however, remains constant. The formula (CO2)8-y·46H2O, where y is the number of vacancies per unit cell, is in keeping with the atomic structure, whereas the traditional formula, CO2·nH2O, where n (hydration number) = 5.75, is misleading.Ambient P-T conditions in the Antarctic and Greenland ice sheets are compatible with sequestering large amounts of carbon as liquid CO2 and/or clathrate. 相似文献
977.
M. Irfan Yesilnacar Erkan Sahinkaya Muhsin Naz Bestamin Ozkaya 《Environmental Geology》2008,56(1):19-25
Monitoring groundwater quality by cost-effective techniques is important as the aquifers are vulnerable to contamination from
the uncontrolled discharge of sewage, agricultural and industrial activities. Faulty planning and mismanagement of irrigation
schemes are the principle reasons of groundwater quality deterioration. This study presents an artificial neural network (ANN)
model predicting concentration of nitrate, the most common pollutant in shallow aquifers, in groundwater of Harran Plain.
The samples from 24 observation wells were monthly analysed for 1 year. Nitrate was found in almost all groundwater samples
to be significantly above the maximum allowable concentration of 50 mg/L, probably due to the excessive use of artificial
fertilizers in intensive agricultural activities. Easily measurable parameters such as temperature, electrical conductivity,
groundwater level and pH were used as input parameters in the ANN-based nitrate prediction. The best back-propagation (BP)
algorithm and neuron numbers were determined for optimization of the model architecture. The Levenberg–Marquardt algorithm
was selected as the best of 12 BP algorithms and optimal neuron number was determined as 25. The model tracked the experimental
data very closely (R = 0.93). Hence, it is possible to manage groundwater resources in a more cost-effective and easier way with the proposed
model application. 相似文献
978.
Assessment of groundwater vulnerability to pollution in Dire Dawa,Ethiopia using DRASTIC 总被引:1,自引:0,他引:1
Assessment of groundwater vulnerability to pollution is an effective tool for the delineation of groundwater protection zones.
DRASTIC approach was used to determine vulnerability zones in Dire Dawa groundwater basin, a semiarid region of Ethiopia.
Maps of the seven DRASTIC parameters were prepared. GIS-ArcView was used for mapping and performing weighted-overlay analysis.
The result of the analysis indicated that eastern part of the study area, in which Dire Dawa town is located, is highly vulnerable.
A low aquifer vulnerability class was determined for the western portion of the study area as a result of greater groundwater
depths, higher relative soil-clay content, and relatively low recharge rates for this area. The area between the two zones
is of medium vulnerability. Observed nitrate concentrations in boreholes are in accordance with the vulnerability map. Some
of the boreholes in the Sabian well field (Dire Dawa area) already deliver groundwater with nitrate levels significantly exceeding
health standards set by the World Health Organization, while boreholes in the western part (low vulnerability zone) contain
almost no nitrate. The result of this study is useful for risk assessments and for the development of effective groundwater
management strategies for this region and others like it. 相似文献
979.
The metalized quartz veins is located 5 km west of the Iraqi-Iran border in the Qandil range. The quartz veins included sulfide and oxide ore minerals which mostly occur in the form of open-space filling texture. The polymetallic mesothermal quartz veins are hosted by marble and phyllite rocks. Within these veins, multiphase, open-space filling and crustiform, bedding to massive textures with pyrite, sphalerite, galena, chalcopyrite,galena, sphalerite, tenorite, azurite, and malachite are observed. Selected samples were analyzed by using ore microscopy and electron probe micro analyzer (EPMA) and scanning electron microscope (SEM). Ore minerals show replacement textures. The paragenesis diagram was made from a careful study of polished sections and three stages have been identified including pre-stage mineralization, mineralization, and post-mineralization stages.Fluid inclusion microthermometric analysis of 15 primary inclusions of quartz veins indicated that ore mineralization at the studied area were formed by a mesothermal, low to medium density, and dilute NaCl-type fluid system. The source of the fluid is mostly metamorphic which became mixed with other fluids later. Hydrothermal fluids of the selected studied area were classified into two groups based on microthermometry study; the first group had a higher homogenization temperature (335.5 to 386.8 °C) than the second group (194.1 to 298.5 °C), with a small difference in salinity between them. Nearly each group has different complexes including chloride and sulfide complexes respectively. The results of stable sulfur isotope of the ore minerals (chalcopyrite and sphalerite) confirmed the sedimentary and/or metamorphic origin of the ore mineralization. 相似文献
980.
Growth of large sulfide structures on the endeavour segment of the Juan de Fuca ridge 总被引:1,自引:0,他引:1
Mapping and sampling with DSRV “Alvin” has established that sulfide blocks 0.5 m across, dredged from the axial valley of the Endeavour Segment at 47°57′N, are samples of unusually large sulfide structures. The steep-sided structures, up to 30 m in length, 20 m in height, and 10–15 m across, are localized by venting along normal faults at the base of the western axial valley wall, and are distributed for about 200 m along strike paralleling the 020 trend of the ridge crest. High-temperature fluids (350 to more than 400°C) pass through the massive sulfide structures and enter seawater through small, concentric “nozzle-like” features projecting from the top or the sides of the larger vent structures. Diffuse, low-temperature flow is pervasive in the vicinity of the active sulfide structures, exiting from basalt and sulfide surfaces alike. Evidence of recent volcanic activity is sparse.The two largest samples taken with the dredge would not have been recoverable using the submersible. These samples represent massive, complex portions of the sulfide structures which were not closely associated with rapid high-temperature fluid flow at the time of sampling; they contain textural evidence of sealed hydrothermal fluid exit channels. Mineralogy is dominated by Fe sulfides nnd amorphous silica. Pyrite, marcasite, wurtzite, chalcopyrite, and iss are the most common sulfide phases. Pyrrhotite, galena, and sphalerite are present in trace amounts. Barite, amorphous silica, and chalcedony are the only non-sulfide phases; anhydrite is not observed in any of the dredge samples, although it is common in the chimney-like samples recovered by “Alvin”.Specific mineralogical-textural zones within the dredge samples are anaoogous to individual layers in East Pacific Rise at 21°N and southern Juan de Fuca Ridge samples, with two exceptions: a coarse-grained, highly porous Fe sulfide-rich interior containing sulfidized tubeworm casts, and a 2–5 cm thick zone near the outer margin of the samples dominated by late stage amorphous silica. The porous interior may have formed by dendritic crystal growth from a slowly circulating fluid within a large enclosed chamber. The amorphous silica deposited from a seawater/hydrothermal fluid mixture percolating slowly through the walls of the enclosed chamber; conductive cooling of the fluid as it traversed the walls allowed amorphous silica to precipitate. These silica-rich zones are the densest, most durable portions of the structures and may be responsible for the lasting stability of the large sulfide features.Observations in these samples are consistent with two distinct phases of development. Phase 1 is analogous to chimney growth and construction at 21°N and ends when flow channels become sealed to rapid flow of through-going fluid. The flow is evidently redirected within the structure. Phase 2 includes dissolution of anhydrite and precipitation of amorphous silica during conductive cooling of sluggishly circulating hydrothermal fluid or seawater/hydrothermal fluid mixtures. Evolution of vent structures through phase 2 allows lateral and vertical growth of unusually large structures. 相似文献