The role of the 1999 Chamoli earthquake in the formation of ground cracks     

Irene Sarkar 《Journal of Asian Earth Sciences》2004,22(5):529

The moderate magnitude Chamoli earthquake that occurred in the Garhwal Higher Himalaya, in the early hours of March 29, 1999, caused intense damage to the ground and mountain slopes of the Alaknanda–Mandakini river valley and adjoining region. A systematic survey of this induced damage was conducted immediately after the earthquake occurred. Prominent shallow cracks of significant length, negligible width and indeterminate vertical extent, conspicuously tensile in nature, with little or no slip across the crack planes, were observed in the ground at several places along the surveyed route. These cracks had formed in the dynamic phase of the Chamoli earthquake process that is in the period of time during which the earthquake-generated seismic waves were passing through the geographic region of interest. However, we use the theory of earthquake-induced static (or long time) stress changes to visualize such cracks at some selected sites where ground damage was relatively more intense and varied to suggest lower bound estimates of the dynamic stress contributions of the main shock for their formation.Based on the results of our analysis we conclude that, just prior to the earthquake occurrence, under the influence of the local ambient stress field, the ground at these sites was already near failure in tension. To this, in its dynamic phase, the Chamoli earthquake induced stress perturbations, having, across the planes of the cracks, (i) shear components which were nearly equal and opposite to similar components of the ambient stress field and (ii) normal (tensile) components, necessary for triggering tensile failure of the ground. The σ₃ (or minimum principal stress) component of the resultant perturbed failure stress field thus became sufficiently tensile while the transverse stresses became sufficiently insignificant. This facilitated formation of major tensile cracks in the ground there. Our static estimates of the tensile stress changes at the different sites are, in essence, estimates of the minimal triggering stress perturbations that was provided by the Chamoli earthquake in the dynamic state for the formation of the tensile cracks there.  相似文献   

Magnetic fabrics and rock magnetism of Proterozoic dike swarm from the southern São Francisco Craton, Minas Gerais State, Brazil     

Maria Irene Bartolomeu Raposo  Alexandre O. Chaves  Paulo Lojkasek-Lima  Manoel Souza D'Agrella-Filho  Wilson Teixeira   《Tectonophysics》2004,378(1-2):43-63

Magnetic fabric and rock magnetism studies were performed on 32 mafic dikes of a Proterozoic dike swarm from the southern São Francisco Craton (SFC; Minas Gerais State, SE Brazil). Magnetic anisotropies were determined by applying anisotropy of low-field magnetic susceptibility (AMS) and anisotropy of remanent magnetization (ARM). The latter was performed imposing both anhysteretic (total (AAR) and partial pAAR)) and isothermal remanence magnetizations (AIRM). Partial anhysteretic remanence anisotropy was performed based on remanent coercivity spectra from a pilot specimen of each site. In most sites, AMS is dominantly carried by ferromagnetic minerals, however, in some sites, the paramagnetic contribution exceeds 70% of bulk susceptibility. Rock magnetism and thin section analysis allow classifying the dikes as non-hydrothermalized and hydrothermalized. Magnetic measurement shows that the mean magnetic susceptibility is usually lower than 5×10⁻³ (SI). Ti-poor titanomagnetites up to pure magnetite pseudo-single-domain (PSD) grain sizes carry the majority of magnetic fabrics for non-hydrothermalized dikes whereas coarse to fine grained Ti-poor titanomagnetites carry the majority of magnetic fabrics for hydrothermalized dikes.Three primary AMS fabrics are recognized which are coaxial with ARM fabric, except for two dikes, from both non-hydrothermalized and hydrothermalized dikes. Normal AMS fabric surprisingly is not dominant (31%). The parallelism between AMS, pAAR_0–30, pAAR_30–60 and pAAR_60–90 fabrics in the hydrothermalized dikes indicates that magnetic grains formed due to late-stage crystallization or to remobilization of iron oxides due to hydrothermal alteration after dike emplacement have acquired a mimetic fabric coaxial with the primary fabric given by coarse-grained early crystallized Ti-poor titanomagnetites. This fabric is interpreted as magma flow in which the analysis of K_max inclination permitted the inference that the dikes were fed by horizontal or subhorizontal fluxes (K_max<30°). Intermediate AMS fabric is the most important (41%) in the investigated swarm. It is interpreted as due to vertical compaction of a static magma column with the minimum stress along the dike strike. ARM determinations for these sites also remained intermediate except for two dikes. In one of them, AIRM fabric resulted in normal AMS fabric while for the other AAR fabric resulted in inverse AMS fabric. A combination of AMS and ARM fabrics suggest that magmatic fabric for both dikes were overprinted by some late local event, probably related to Brasiliano orogenic processes after dike emplacement. InverseInverse AMS fabric is a minority (four dikes). ARM determinations also remained inverse suggesting a primary origin for inverse AMS fabric.  相似文献   

Microbial dechlorination of HCB,PCP, PCB180, HCH and PCE in a Yangtze Three Gorges Reservoir enrichment culture,China     

Irene Kranzioch-Seipel  Ulrike Beckert  Chaofeng Shen  Daqiang Yin  Andreas Tiehm 《Environmental Earth Sciences》2016,75(10):928

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Assessment of the acid drainage neutralization capacity and the toxic metals lixiviation of tailing from Guanajuato mining district,Mexico   总被引：1，自引：0，他引：1  

María Elena García-Arreola  Luisa María Flores-Vélez  Marcos Loredo-Tovías  Alfredo Aguillón-Robles  Rubén Alfonso López-Doncel  Irene Cano-Rodríguez  Sonia Hortensia Soriano-Pérez 《Environmental Earth Sciences》2018,77(9):355

In Mexico, many environmental problems are generated by large mining activities taking place in several mining districts. These mining activities produce great quantities of residues; large majorities of these have high sulfur content, which could generate acid drainage due to their interaction with the oxygen in the environment. The study area was located in the Mining District of Guanajuato, Mexico with abandoned tailings generated mainly by the gold and silver production. Two areas, called as Monte de San Nicolás (SN) and Peregrina (P) were selected for this study. The results study shows that there was no risk of production of acid drainage, since these tailings contained high amount of carbonates, which neutralized the generation of acidity and consequently decreased the possibility of leaching of some elements. However, not all elements leach in acid pH, as arsenic bound to oxyhydroxides, which is in a basic environment and its increased release by increasing the pH.  相似文献   

Calcification depth and spatial distribution of Thoracosphaera heimii cysts: Implications for palaeoceanographic reconstructions     

Marion Kohn  Karin A.F. Zonneveld 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(12):1543-1560

For the optimal use in palaeoceanographic studies of the stable oxygen isotopic signal and elemental composition of the calcareous photosynthetic dinoflagellate Thoracosphaera heimii, it is essential to gain detailed information about its calcification depth and spatial distribution. We therefore studied the vertical and horizontal distribution patterns of T. heimii in the upper water column (0–200 m) along three transects: an inshore–offshore gradient off Cape Blanc (CB), a south–north transect from CB to the Portuguese coast and a north–south transect off Tanzania. We compared concentrations of living cysts (cells with cell content) with chlorophyll-a, salinity and temperature measurements at the sampling depth. In order to explore the seasonal variability in cyst production, three transect off CB were sampled at three different times of the year.Living T. heimii cysts were found in the upper 160 m of the water column with highest concentrations in the photic zone indicating that the calcification of T. heimii occurs in the upper part of the water column. Maximal abundances of living cysts were found relatively often in or just above the deep chlorophyll maximum (DCM), the depth of which varies regionally from about 20–40 m off CB to about 80 m off Tanzania and along the transect from CB to the Portuguese Coast. However, there was no significant correlation at the 95% confidence level between the cyst concentrations and temperature, salinity and chlorophyll-a concentrations at the sampling depths observed.In both the Atlantic and Indian Oceans, the highest abundances of T. heimii were observed in regions where the upper water masses contained relatively low nutrient concentrations that are influenced only sporadically, or not at all, by enhanced photic zone mixing related to the presence of upwelling cells or river outflow plumes at or close to the sampling sites. The seasonal production of cysts by T. heimii appears to be negatively related to the presence of upwelling filaments across the sampling sites. Our study suggests that turbulence of the upper water masses is a major environmental factor influencing T. heimii production.  相似文献   

Social capital,individual responses to heat waves and climate change adaptation: An empirical study of two UK cities     

Johanna Wolf  W. Neil Adger  Irene Lorenzoni  Vanessa Abrahamson  Rosalind Raine 《Global Environmental Change》2010,20(1):44-52

It has been claimed that high social capital contributes to both positive public health outcomes and to climate change adaptation. Strong social networks have been said to support individuals and collective initiatives of adaptation and enhance resilience. As a result, there is an expectation that social capital could reduce vulnerability to risks from the impacts of climate change in the health sector. This paper examines evidence on the role social networks play in individuals’ responses to heat wave risk in a case study in the UK. Based on interviews with independently living elderly people and their primary social contacts in London and Norwich, we suggest that strong bonding networks could potentially exacerbate rather than reduce the vulnerability of elderly people to the effects of heat waves. Most respondents interviewed did not feel that heat waves posed a significant risk to them personally, and most said that they would be able to cope with hot weather. Bonding networks could perpetuate rather than challenge these narratives and therefore contribute to vulnerability rather than ameliorating it. These results suggest a complex rather than uniformly positive relationship between social capital, health and adaptation to climate change.  相似文献   

Element zoning trends in olivine phenocrysts from a supposed primary high-magnesian andesite: an electron- and ion-microprobe study     

S. C. Kohn  C. M. B. Henderson  R. A. Mason 《Contributions to Mineralogy and Petrology》1989,103(2):242-252

Electron and ion-probe microanalysis have been used to obtain zoning profiles for major and trace elements in olivine phenocrysts from a high-magnesian andesite from Shodo-Shima island, southwest Japan. This rock was previously thought to represent undifferentiated, primary magma. Some crystals have unzoned cores, while others show cores which are reversely zoned with respect to Mg/ (Mg+Fe), Ni, Mn and Cr. In addition, some Ni profiles show a normally zoned hump at the most central portions of the reversely zoned crystals. All crystals show normally zoned rims. The Li concentrations are constant throughout the cores of all crystals studied, but rise sharply, by a factor of up to at least six, in the rims. The Ca and Co concentrations are essentially constant throughout all the crystals. Mechanisms for producing the observed zoning profiles are discussed, and it is concluded that the reverse zoning was produced by the introduction of crystals into a less differentiated magma than that in which they grew. The reversely zoned crystals could therefore represent xenocrysts which were introduced into an undifferentiated magma, or phenocrysts introduced into a more primitive magma by a magma mixing process. The Ni profiles are used to estimate the residence time of these crystals in the more primitive magma. The following trace element partition co-efficients have been estimated for the olivine-groundmass system in this rock: D ^Ni=16; D ^Mn=1.1; D ^Co=4.2; D ^Ca =0.02; D ^Ti=0.005; D ^V=0.05; D ^Sc=0.2; D ^Na=0.0002. Studies of trace element zoning will become increasingly important as the new generation of trace element microprobes become available but a larger database of experimentally determined values for trace element partition coefficients and diffusion coefficients in crystals and magmas, and a better understanding of other disequilibrium processes are required to fully exploit the new data.  相似文献   

Bacterial contribution to sedimentary organic matter; a comparative study of lipid moieties in bacteria and Recent sediments     

H. Goossens  W. Irene  C. Rijpstra  R.R. Düren  J.W. De Leeuw  P.A. Schenck 《Organic Geochemistry》1986,10(4-6)

A systematic study of the lipid composition of thirteen bacterial species and three Recent sediments (methanogenic sediment, cyanobacterial mat and evaporative gypsum crust) was undertaken in an attempt to recognize bacterial organic matter in sediments. A sequential method, which distinguishes between three different modes of occurrence of lipid moieties (free, OH⁻- and H⁺-labile), was applied. The acid-labile fractions are discussed.The three main groups of bacteria, archaebacteria, gram-positive eubacteria and gram-negative eubacteria, are easily distinguished. Methanogenic and extremely halophilic archaebacteria are characterized by the presence of diphytanyl glyceryl ether and the absence of fatty acids. The gram-positive eubacteria contain primarily iso- and anteiso-branched fatty acids whereas the gram-negative bacteria and sediments are dominated by β- and α-hydroxy fatty acids. A wide variety of H⁺-labile hydroxy fatty acids was observed which included several, as yet unknown, structures.β-Hydroxy fatty acids in this H⁺-labile mode of occurrence are exclusively present in bacteria. Their distribution patterns in sediments are considered “fingerprints” of past and present bacterial populations. The specific differences in β -hydroxy fatty acid compositions observed in the different bacteria and the three sediments investigated, suggest that amide-linked β-hydroxy fatty acid patterns are useful as markers of bacterial populations and therefore of environmental conditions.  相似文献   

Modelling the variability of midlatitude storm activity on decadal to century time scales   总被引：1，自引：0，他引：1  

Irene Fischer-Bruns  H. von Storch  J. F. González-Rouco  E. Zorita 《Climate Dynamics》2005,25(5):461-476

The output of several multi-century simulations with a coupled ocean–atmosphere general circulation model is examined with respect to the variability of global storm activity in winter on time scales of decades and longer. The frequency of maximum wind speed events within a grid box, using the lower limits on the Beaufort wind speed scale of 8 and 10 Bft as thresholds, is taken as the characteristic parameter. Two historical climate runs with time-dependent forcing of the last five centuries, one control simulation, and three climate change experiments are considered. The storm frequency shows no trend until recently. Global maps for the industrially influenced period hardly differ from pre-industrial maps, even though significant temperature anomalies temporarily emerge in the historical runs. Two indicators describing the frequency and the regional shift of storm activity are determined. In historical times they are decoupled from temperature. Variations in solar and volcanic forcing in the historical simulations as well as in greenhouse gas concentrations for the industrially influenced period are not related to variations in storm activity. Also, anomalous temperature regimes like the Late Maunder Minimum are not associated with systematic storm conditions. In the climate change experiments, a poleward shift of storm activity is found in all three storm track regions. Over the North Atlantic and Southern Ocean, storm activity increases, while it decreases over the Pacific Ocean. In contrast to the historical runs, and with the exception of the North Pacific storm frequency index, the storm indices parallel the development of temperature, exceeding the 2 σ-range of pre-industrial variations in the early twenty-first century.  相似文献   

Investigation of waste disposal areas using electrical methods: a case study from Chania,Crete, Greece   总被引：1，自引：0，他引：1  

Pantelis Soupios  Ilias Papadopoulos  Maria Kouli  Irene Georgaki  Filippos Vallianatos  Eleni Kokkinou 《Environmental Geology》2007,51(7):1249-1261

A geophysical investigation of a landfill area was conducted as inextricable phase of a preliminary geotechnical, geological and hydrogeological study of the area under investigation. Electrical resistivity tomography (ERT), one of the most promising prospecting techniques mainly concerning its effective contribution to resolve several environmental problems, was applied for the geophysical modeling. ERT is a robust imaging method the theory and implementation of which are well documented in geophysical research literature. The survey site is located in Akrotirion Peninsula, about 7 km east of Chania city in Crete I. The geological setting comprises Trypalion limestones, marly limestones and a clayed weathered layer. Cavities are also identified at various scales which are recent tectono-karstic voids. Due to the above-mentioned geological singularity and in the light of the requirement for an environmentally safe construction of the landfill, an ERT survey was carried out. Specifically, seven geoelectrical tomographies were conducted reaching the prospecting depth of 36 m. The resulted images conduced, to overcome geotechnical problems since the spatial distribution of karstic voids was determined, to plan the future sites for waste disposal as the geological conditions were studied in detail and to reliably estimate the thickness of the already deposited wastes. The resulted images were confirmed using available borehole logs and ambient noise measurements.  相似文献