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261.
Zedník J. Pospíšil J. Růžek B. Horálek J. Boušková A. Jedlička P. Skácelová Z. Nehybka V. Holub K. Rušajová J. 《Studia Geophysica et Geodaetica》2001,45(3):267-282
In the time span from January 1995 to December 1999 the Czech National Seismological Network (CNSN), consisting of ten permanent digital broadband stations, several local networks and two data centers, detected and recorded 9530 regional natural seismic events, 27 greater than magnitude 2. Most of these events were located by the Czech Seismological Service (CSS), and the most prominent of them were analyzed in detail. A large number of quarry blasts were recorded as well but were not included in the analysis. We provide basic information on the configuration of the CNSN and on the way of routine data processing employed by the CSS in this paper. The over-all regional seismicity monitored by the CNSN in 1995–1999 is briefly reviewed. The main results of observations and evaluation of the local (NW-Bohemia/Vogtland, South Bohemia, Sudeten) and induced (Kladno, Píbram, Upper Silesia, Lubin/Poland) seismic activity within this period are presented in a condensed form. Finally, a summary on macroseismic observations on the territory of the Czech Republic in 1995–1999 is also presented. 相似文献
262.
Jan Šafanda Philipp Heidinger Helmut Wilhelm Vladimír Čermák 《Hydrogeology Journal》2007,15(2):423-428
As part of the International Continental Scientific Drilling Program (ICDP), the 1.5-km-deep borehole Yaxcopoil-1, located in the Chixculub meteor impact structure in Mexico, has undergone further study after drilling operations ceased. Temperature logs were repeated ten times at intervals 0.3–0.8, 15, 24 and 34 months after borehole shut-in. The logs bear a distinct signature of transient heat transfer by groundwater flow manifested by a gradual distortion of the linear temperature profile when a cold wave of 0.8–1.6°C amplitude was detected propagating downward from 145 to 312 m at a rate of 4–6 m/month. To understand the nature of this moving anomaly, a 20-day monitoring of the cold wave was carried out at a depth of 307 m that showed further cooling of 0.6°C during the first 16 days of the passage followed by temperature stabilisation. As an explanation of this unusual phenomenon, a theory is proposed, whereby the drilling mud has accumulated within the overlying and cooler highly porous and permeable karstic rocks during the drilling and migrates downward. The observed migration rate suggests a permeability higher than 10?11 m2. This indicates a high vulnerability to contamination of the only freshwater aquifer in the Yucatan region. 相似文献
263.
Javier Palarea-Albaladejo Josep A. Martín-Fernández Juan Gómez-García 《Mathematical Geology》2007,39(7):625-645
In this work, a parametric approach for replacing data below the detection limit, also known as rounded zeros, in compositional
data sets is proposed. Compositional rounded zeros correspond to small proportions of some whole that cannot be reliably detected
by the analytical instruments under given operating conditions. This kind of zeros appear frequently in the data collection
process in geosciences. They must be treated in an adequate way before some multivariate analysis can be applied. Our procedure
results from a modification of the Expectation-Maximization (EM) algorithm and is based on the additive log-ratio transformation.
Its coherence with the nature of compositional data and with basic operations in the simplex sample space is checked. Using
real data sets, we find that this approach improves other parametric and non-parametric techniques for compositional rounded
zeros. 相似文献
264.
María Gabriela García Ondra Sracek Diego Sebastián Fernández Margarita del Valle Hidalgo 《Environmental Geology》2007,52(7):1261-1275
The concentration of arsenic measured in groundwater from three aquifers in the study area located in the Eastern Tucuman
province, Argentina, mostly depends on the lithology, but the spatial and temporal variations of concentrations seem to be
also controlled by pH changes, climatic factors, and human perturbations. The highest concentrations of As (more than 1,000 μg
L−1) were found in the shallow aquifer, made of As-rich loess, while the lowest concentrations were measured in the deep confined
aquifer, consisting of alternating layers of alluvial sands/gravels and clays. Intermediate values were measured in the semiconfined
aquifer made of the fluvial sediments deposited in the Salí River valley, that alternate in the upper part of the sedimentary
sequence with layers of loess. Because most of As in the loess is considered to be adsorbed onto Fe-oxyhydroxide coatings,
the increase of pH in the flow direction (west-east) leads to increasing arsenic concentrations towards the eastern border
of the study area. The decomposition of organic wastes poured into the Salí River or associated with local and diffuse sources
of contamination in the eastern part of the study area depletes dissolved oxygen, which leads to the reductive dissolution
of Fe and Mn oxyhydroxides, and to the subsequent release of the adsorbed and co-precipitated As. This process mainly affects
shallow groundwater and the upper part of the semiconfined aquifer. Geochemical and hydrological data also suggest that rising
water table levels at the end of the wet season may also lead to reductive dissolution of As-rich Fe oxyhydroxides in the
shallow aquifer. 相似文献
265.
Oscar Escolero Luis E. Marin Eloisa Domínguez-Mariani Sandra Torres-Onofre 《Environmental Geology》2007,51(5):719-723
A hydraulic analysis of the interface between freshwater–saltwater behavior was done in the Merida Yucatan zone, two machines
that constantly register the groundwater levels were installed, and three electric conductivity logs were taken from wells.
When comparing the measured results with the ones obtained using theoretical equations developed to calculate the freshwater–saltwater
interface position, it was proved that in some cases these equations can be applied, and in others not. Two effects that rule
the behavior of karst aquifers in extraordinary conditions were found. 相似文献
266.
I. Camilo Higuera-Díaz Philip J. Carpenter Michael D. Thompson 《Environmental Geology》2007,53(4):805-812
Karst aquifers are highly susceptible to contamination, with numerous points of entry for contaminants through recharge features
such as sinkholes, swallow holes and solutionally enlarged fractures. These recharge features may be filled or obscured at
the surface, requiring the use of geophysical or remote sensing techniques for their identification. This study uses seismic
refraction data collected at the Ft. Campbell Army Airfield (CAAF), Kentucky, USA, to test the hypothesis that refraction
tomography is a useful tool for imaging bedrock depressions beneath thick overburden (greater than 20 m of unconsolidated
sediment). Southeast of the main taxiway of CAAF seismic velocity tomograms imaged a bedrock low, possibly a closed depression,
at a depth of 25 m that had been earlier identified through delay-time analysis of the same refraction data. Tomography suggests
the bedrock low is about 250-m wide by 10-m deep at its widest point. High rates of contaminant vapor extraction over the
western extension of this feature suggest a high concentration of contaminants above, and within, this filled bedrock low,
the base of which may contain solutionally enlarged fractures (i.e. karst conduits) that could funnel these contaminants to
the upper or lower bedrock aquifers. This study thus demonstrates the viability of seismic refraction tomography as a tool
for identification of filled sinkholes and bedrock depressions in karst areas. 相似文献
267.
North End Lake is a polluted and eutrophic freshwater system located in Port Elizabeth, South Africa. Since the lake is expected
to be used for recreational/tourist purposes by 2010, a rehabilitation program will have to be designed. For this reason,
we retrieved a sediment core from the central region of the lake to decipher the effect of historical human impacts on the
water body. Pre-disturbance paleolimnological inferences indicate that the lake was likely mesotrophic. After ∼1831, when
sheep farming activities were undertaken in the catchment, increases in trophic state and changes in sediment composition
were observed. After ∼1937, increases in trace metal levels, organic matter, spheroidal carbonaceous particles (SCP) and changes
in sediment composition were recorded. The system became eutrophic as indicated by the dominance of the diatom Actinocyclus normanii, a cosmopolitan species often observed in systems where water quality has been dramatically degraded. The conditions worsened
after 1986 because of the construction of a storm-water retention system, which intentionally channeled storm-water runoff
into the lake. Because of this, extremely high values of fecal coliforms (i.e. 2 × 106 every 100 ml) have been measured in the water column. The paleolimnological information identified the sharp increase in
organic content in the uppermost section of the core, and this could be correlated to the operation of the storm-water retention
system. Therefore, as an immediate management measure, we suggest that the storm-water retention system should either no longer
be utilized, or the storm-water runoff should be treated before disposal into the lake. In addition, an effective sewage system
has to be constructed. 相似文献
268.
Andreas Macrander Rolf H. Käse Uwe Send Héðinn Valdimarsson Steingrímur Jónsson 《Ocean Dynamics》2007,57(2):75-89
In spite of the fundamental role the Atlantic Meridional Overturning Circulation (AMOC) plays for global climate stability,
no direct current measurement of the Denmark Strait Overflow, which is the densest part of the AMOC, has been available until
recently that resolve the cross-stream structure at the sill for long periods. Since 1999, an array of bottom-mounted acoustic
instruments measuring current velocity and bottom-to-surface acoustic travel times was deployed at the sill. Here, the optimization
of the array configuration based on a numerical overflow model is discussed. The simulation proves that more than 80% of the
dense water transport variability is captured by two to three acoustic current profilers (ADCPs). The results are compared
with time series from ADCPs and Inverted Echo Sounders deployed from 1999 to 2003, confirming that the dense overflow plume
can be reliably measured by bottom-mounted instruments and that the overflow is largely geostrophically balanced at the sill. 相似文献
269.
Wagner José Barreto Ieda Scarminio Maria Cristina Solci Dílson Norio Ishikawa Melissa Tiemi Ogasawara Sônia Naomi Nomi Sônia Regina Giancoli Barreto 《洁净——土壤、空气、水》2007,35(3):239-245
Seventeen physical and chemical parameters were obtained from a hydroelectric reservoir located in a tropical region in the south of Brazil. Multivariate Principal Component Analysis (PCA) and Hierarchical Group Analysis (HGA) were used to identify the parameters discriminating the origin of water from the Tibagi and the Primeiro de Maio River, after it has passed the mixing region. The study was conducted during the dry and rainy seasons in July 2002 and February 2003 at three depths and three sampling sites located 0, 5, and 10 km away from the mixing region. The statistical methods showed to be appropriate for identifying the contribution of each tributary in the water mixing site of a complex water system. The most important discriminating parameter was the absorbance relation A(253 nm)/A(203 nm), followed by the concentrations of Fe(III), Mn(III), and Ni(II). An anthropogenic interference was found in the reservoir due to high Ni(II) and orthophosphate concentrations caused by a nearby town sewage discharge. The interference was more important during the dry periods due to the lower dispersion of the pollutants. Urgent initiatives should be taken from the state government to build treatment stations for the wastewater of the small cities around the Capivara hydroelectric reservoir to prevent the drinking water quality from deteriorating. 相似文献
270.
Analysis of the weightiness of site effects on reinforced concrete (RC) building seismic behaviour: The Adra town example (SE Spain) 总被引:1,自引:0,他引:1
Manuel Navarro Francisco Vidal Takahisa Enomoto Francisco J. Alcalá Antonio García‐Jerez Francisco J. Sánchez Norio Abeki 《地震工程与结构动力学》2007,36(10):1363-1383
The damage distribution in Adra town (south‐eastern Spain) during the 1993 and 1994 Adra earthquakes (5.0 magnitude), that reached a maximum intensity degree of VII (European Macroseismic Scale (EMS scale)), was concentrated mainly in the south‐east zone of the town and the most relevant damage occurred in reinforced concrete (RC) buildings with four or five storeys. In order to evaluate the influence of ground condition on RC building behaviour, geological, geomorphological and geophysical surveys were carried out, and a detailed map of ground surface structure was obtained. Short‐period microtremor observations were performed in 160 sites on a 100m × 100m dimension grid and Nakamura's method was applied in order to determine a distribution map of soil predominant periods. Shorter predominant periods (0.1–0.3 s) were found in mountainous and neighbouring zones and larger periods (greater than 0.5 s) in thicker Holocene alluvial fans. A relationship T = (0.049 ± 0.001)N, where T is the natural period of swaying motion and N is the number of storeys, has been empirically obtained by using microtremor measurements at the top of 38 RC buildings (ranging from 2 to 9 storeys). 1‐D simulation of strong motion on different soil conditions and for several typical RC buildings were computed, using the acceleration record in Adra town of the 1993 earthquake. It is noteworthy that all the aforementioned results show the influence of site effects in the degree and distribution of observed building damage. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献