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991.
The No. 6 Coal-bed from the Heidaigou Mine, Jungar Coalfield, Inner Mongolia is a super-large Ga deposit. The dominant carrier of Ga is boehmite in coal. The study of coal facies may provide genetic enrichment information of Ga and its carrier (boehmite) in the Ga deposit. On the basis of study on coal petrology and mineralogy, it was found that the No. 6 Coal-bed from the Heidaigou Mine of Jungar was enriched in inertinites and the microlitho-types were dominated by clarodurite. The maceral morphological features and association indicate that the coal-bed was formed in a dry sedimentary environment or in a periodic dry sedimentary environment caused by the alternating variations of groundwater level. The optimum conditions for the enrichment of Ga and its particular carrier (boehmite) were dominated by four transitional conditions: (1) the upper delta plain which was the transitional zone between alluvial and lower delta plains, (2) the transitional zone between the dry and wet forest swamps, being slightly apt to the dry one, (3) the transitional tree density between the thick and loose ones, and (4) the low moor that was the transitional zone between two high moors during peat accumulation. 相似文献
992.
993.
Anomaly analysis is used for various geophysics applications such as determination of geophysical structure's location and
border detections. Besides the classical geophysical techniques, artificial intelligence based image processing algorithms
have been found attractive for geophysical anomaly analysis. Recently, cellular neural networks (CNN) have been applied to
geophysical data and satisfactory results are reported. CNN provides fast and parallel computational capability for geophysical
image processing applications due to its filtering structure. The behavior of CNN is defined by two template matrices that
are adjusted by a properly supervised learning algorithm. After training stage for geophysical data, Bouguer anomaly maps
can be processed and analyzed sequentially. In this paper, CNN learning and processing capability have been improved, combining
Wavelet functions and backpropagation learning algorithms. The new architecture is denoted as Wavelet-Cellular Neural networks
(Wave-CNN) and it is employed to analyze Bouguer anomaly maps which are important to extract useful information in geophysics.
At first, Wave-CNN performance is tested on synthetic geophysical data, which are created by a computer environment. Then,
Bouguer anomaly maps of the Dumluca iron ore field have been analyzed and results are reported in comparison to real drilling
results. 相似文献
994.
This article points out some particular features conditioning seismic hazard assessments (SHA) in Spain, a region with low–moderate
seismicity. Although sized earthquakes occurred in the past, as evidenced by historical documents and neotectonic studies,
no large events occurred during the last decades. The absence of strong motion records corresponding to earthquakes with magnitude
larger than 5.5 is an important obstacle for the development of ground motion models constrained by local data, with the consequent
difficulty in SHA studies. In this paper, some recent developments aiming at providing solutions to these difficulties are
presented. Specifically, a strong motion databank containing a massive collection of accelerograms and response spectra from
different configurations source-path-site corresponding to earthquakes all over the world is introduced, together with software
utilities for its management. A first application of this databank is the development of specific ground motion models for
Spain and for the Mediterranean region that predict peak ground accelerations as a function of several definitions of magnitude,
distance and soil class. The predictive power of these ground motion models is tested by contrasting their estimates with
recently recorded ground motions. The comparison between our ground-motion models with others proposed in the literature for
other areas reveals a regular overestimation of the expected ground motions at Spanish sites by the non-local models. Consequently,
SHA studies based in external models may overestimate the predicted hazard at the Iberian sites. In the last part of the paper
a method for checking whether the response spectra proposed in the Spanish Building Code (NCSE-02) are consistent with actual
accelerometric data from recent low magnitude earthquakes is applied. The spectral shapes of the Spanish Building Code NCSE-02
are compared with the response spectral shapes deduced from the available accelerograms by normalising the response spectra
with the recorded PGA. It is appreciated that the NCSE-02 spectral shapes are exceeded by a large number of actual spectral
shapes for short periods (around 0.2 s), a result to be taken into account in further revisions of the NCSE-02 code. The issues
tackled in this work constitute not only an improvement for ground-motion characterisation in Spain, but also provide guidelines
of general interest for potential applications in other regions with similar seismicity. 相似文献
995.
Ocean/ice interaction at the base of deep-drafted Antarctic ice shelves modifies the physical properties of inflowing shelf
waters to become Ice Shelf Water (ISW). In contrast to the conditions at the atmosphere/ocean interface, the increased hydrostatic
pressure at the glacial base causes gases embedded in the ice to dissolve completely after being released by melting. Helium
and neon, with an extremely low solubility, are saturated in glacial meltwater by more than 1000%. At the continental slope
in front of the large Antarctic caverns, ISW mixes with ambient waters to form different precursors of Antarctic Bottom Water.
A regional ocean circulation model, which uses an explicit formulation of the ocean/ice shelf interaction to describe for
the first time the input of noble gases to the Southern Ocean, is presented. The results reveal a long-term variability of
the basal mass loss solely controlled by the interaction between waters of the continental shelf and the ice shelf cavern.
Modeled helium and neon supersaturations from the Filchner–Ronne Ice Shelf front show a “low-pass” filtering of the inflowing
signal due to cavern processes. On circumpolar scales, the simulated helium and neon distributions allow us to quantify the
ISW contribution to bottom water, which spreads with the coastal current connecting the major formation sites in Ross and
Weddell Seas.
相似文献
Christian B. RodehackeEmail: |
996.
O'Leary González Leonardo Alvarez Mariangela Guidarelli Giuliano F. Panza 《Pure and Applied Geophysics》2007,164(10):1985-2007
An overview of the crust and upper mantle structure of Central America and the Caribbean region is presented as a result of
the processing of more than 200 seismograms recorded by digital broadband stations from SSSN and GSN seismic networks. Group
velocity dispersion curves are obtained in the period range from 10s to 40s by FTAN analysis of the fundamental mode of the
Rayleigh waves; the error of these measurements varies from 0.06 and 0.09 km/s. From the dispersion curve, seven tomographic
maps at different periods and with average spatial resolution of 500 km are obtained. Using the logical combinatorial classification
techniques, eight main groups of dispersion curves are determined from the tomographic maps and eleven main regions, each
one characterized by one kind of dispersion curves, are identified. The average dispersion curves obtained for each region
are extended to 150s by adding data from a larger-scale tomographic study (Vdovin et al., 1999) and inverted using a nonlinear procedure. A set of models of the S-wave velocity vs. depth in the crust and upper
mantle is found as a result of the inversion process. In six regions we identify a typically oceanic crust and upper mantle
structure, while in the other two the models are consistent with the presence of a continental structure. Two regions, located
over the major geological zones of the accretionary crust of the Caribbean region, are characterized by a peculiar crust and
upper mantle structure, indicating the presence of lithospheric roots reaching, at least, about 200 km of depth. 相似文献
997.
Strong near-fault ground motion, usually caused by the fault-rupture and characterized by a pulse-like velocity- wave form, often causes dramatic instantaneous seismic energy (Jadhav and Jangid 2006). Some reinforced concrete (RC) bridge columns, even those built according to ductile design principles, were damaged in the 1999 Chi-Chi earthquake. Thus, it is very important to evaluate the seismic response of a RC bridge column to improve its seismic design and prevent future damage. Nonlinear time history analysis using step-by-step integration is capable of tracing the dynamic response of a structure during the entire vibration period and is able to accommodate the pulsing wave form. However, the accuracy of the numerical results is very sensitive to the modeling of the nonlinear load-deformation relationship of the structural member. FEMA 273 and ATC-40 provide the modeling parameters for structural nonlinear analyses of RC beams and RC columns. They use three parameters to define the plastic rotation angles and a residual strength ratio to describe the nonlinear load- deformation relationship of an RC member. Structural nonlinear analyses are performed based on these parameters. This method provides a convenient way to obtain the nonlinear seismic responses of RC structures. However, the accuracy of the numerical solutions might be further improved. For this purpose, results from a previous study on modeling of the static pushover analyses for RC bridge columns (Sung et al. 2005) is adopted for the nonlinear time history analysis presented herein to evaluate the structural responses excited by a near-fault ground motion. To ensure the reliability of this approach, the numerical results were compared to experimental results. The results confirm that the proposed approach is valid. 相似文献
998.
Sara Casciati 《地震工程与工程振动(英文版)》2007,6(3):259-268
The joints connecting vertical and horizontal elements are the "weak link" in structural systems assembled from wood panels. If they are too weak, local failures may occur, resulting in performance that is significantly below expectations. If they are too resistant, the joints may be unable to dissipate energy during vibrations, thus possibly initiating a fast progressive failure. This paper re-processes and re-elaborates the results of shaking table tests previously carried out by the author and other co-workers. The goal is to assess the feasibility of a joint which is able to dissipate energy during vibration, without degrading the connection performance. 相似文献
999.
The dynamic equations of motion of asymmetric offshore platforms under three different environmental conditions:seismic action,wave action and their combination are established in this paper. In establishing these motion equations,three typical eccentricity types including mass eccentricity,rigidity eccentricity and their combination were considered,as are eccentricities that occur un-idirectionally and bi-directionally. The effects of the eccentricity type,the dynamic characteristics and the environmental conditions on the torsional coupling response of platforms are investigated and compared. An effort has also been made to analyze the inffluence of accidental eccentricity on asymmetric platforms with different eccentricity in two horizontally orthogonal directions. The results are given in terms of non-dimensional parameters,accounting for the uncoupled torsional to lateral frequency ratio. Numerical results reveal that the eccentricity type has a great inffluence on the torsionally coupled response under different environmental conditions. Therefore,it is necessary to consider the combination of earthquake and wave action in the seismic response analysis of some offshore platforms. 相似文献
1000.
In this paper, we present a new method for seismic stratigraphic absorption compensation based on the adaptive molecular decomposition.
Using this method, we can remove most of the effects resulting from wavelets truncation and interference which usually exist
in the common time-frequency absorption compensation method. Based on the assumption that the amplitude spectrum of the source
wavelet is smooth, we first construct a set of adaptive Gabor frames based on the time-variant properties of the seismic signal
to transform the signal into the time-frequency domain and then extract the slowly varying component (the wavelet’s time-varying
amplitude spectrum) in each window in the time-frequency domain. Then we invert the absorption compensation filter parameters
with an objective function defined using the correlation coefficients in each window to get the corresponding compensation
filters. Finally, we use these filters to compensate the time-frequency spectrum in each window and then transform the time-frequency
spectrum to the time domain to obtain the absorption-compensated signal. By using adaptive molecular decomposition, this method
can adapt to isolated and overlapped seismic signals from the complex layers in the inhomogeneous viscoelastic medium. The
viability of the method is verified by synthetic and real data sets. 相似文献