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991.
992.
Comparison of source parameters estimated in the frequency and time domains for seismic events at the Rudna copper mine,Poland 总被引:3,自引:0,他引:3
Source parameters estimated in the frequency domain for 100 selected seismic events from the Rudna copper mine, with moment
magnitude ranging from 1.4 to 3.6, were collected to study their scaling relations and to compare them with the parameters
estimated in the time domain. The apparent stress and static stress drop, corrected for the limited bandwidth recording, increase
slightly in a similar manner with increasing seismic moment. The ratio of apparent stress to static stress drop, a measure
of radiation efficiency, is practically constant and its mean value is close to 0.1.
For 37 seismic events, with moment magnitude between 1.9 and 3.4, source parameters were estimated in the time domain from
relative source time functions, that displayed unilateral rupture propagation, and their rupture velocity could be estimated.
It ranges from 0.23 to 0.80 of shear wave velocity and is almost independent of seismic moment. The fault length, estimated
from the average source pulse width and rupture velocity, is clearly dependent on seismic moment and is smaller than the source
radius estimated from the corner frequency on the average by about 25 percent. There is no correlation between the values
of static stress drop estimated in the frequency and time domains, but the time domain stress drop is in general similar to
that estimated in the frequency domain. The apparent stress increases with increasing rupture velocity, and the ratio of apparent
stress to static stress drop seems also to depend on rupture velocity. 相似文献
993.
泥质烃源岩密度分级分离与有机碳分配 总被引:4,自引:0,他引:4
选取东营凹陷第三系11 块泥质烃源岩样品,粉碎后按小于1.6 g/cm3,1.6~2.2 g/cm3 和大于2.2 g/cm3 的密度,分离成1,2,3 三个组分,希望可以把烃源岩中游离的有机质、无机矿物与有机黏土复合体分别提取出来。对各组分进行质量、有机碳及扫描电镜分析,探讨不同密度组分中有机质赋存形式及有机碳分配方式的差异性。密度分组后各组分的质量、有机碳量回收率基本上达到100%,表明密度分离方法可信,且对烃源岩的破坏较弱。通过扫描电镜观察发现,1 组分中存在大量的生物碎屑有机质,经盐酸处理后,有机质颗粒表面干净,而2,3 组分中只见有大量的矿物颗粒,但能谱分析显示了C 元素的存在。这些特征表明1 组分为生物碎屑有机质,而2,3 组分中有机质与无机矿物相混合。有机碳分析表明,1 组分有机碳含量平均高达14.24%,但其仅占全岩有机碳量的1.11%;2,3 组分中有机碳含量分别为3.26%,2.77%,两者占全岩有机碳量的90% 以上。由此看来与无机矿物相结合是烃源岩中有机质较为重要的赋存方式,这部分有机质对全岩生烃量的贡献不容忽视。 相似文献
994.
This paper raises fundamental questions about the sole use of paleolimnological techniques to identify sediment sources and
develop catchment management plans. The concept of an integrated lake: catchment framework was established 30 years ago, yet
paleolimnologists occasionally fail to appreciate the dynamics of the contributing catchment. This is especially critical
when the predominant source of sediment accumulating in a lake is allochthonous. In this paper we argue that a detailed appraisal
of catchment sources and investigation of historical documentary evidence is needed to identify and evaluate the relative
significance of sediment sources. We used such an approach at Aqualate Mere, Shropshire, UK. Mineral magnetic and radionculide
signatures of potential catchment sources and accumulating lake sediments were compared in an attempt to match the sources
to sediments deposited in the Mere. Dated lake sediments indicate there has been an increase in sedimentation rate and the
relative amount of minerogenic material delivered to the Mere over the last 200 years. In contrast to a previous study at
the same site, there is no evidence to attribute this increase to an overspill from a nearby canal. Other catchment disturbances
include landscaping in parkland surrounding the Mere in the early nineteenth century and drainage systems installed to improve
catchment agriculture over the last ca. 150 years. Both activities may explain the change in sedimentation rates and types,
independent of the hypothesized canal origin. Although our results exclude the canal as a major sediment source, identifying
the contribution of other potential catchment sources remains problematic. 137Cs inventories for the lake are similar to those recorded at a local reference site, suggesting little influx of 137Cs-bearing topsoil, yet 137Cs activities remain high in the upper 20–30 cm of the lake sediment profile, indicating a topsoil origin. Combined radionuclide
and mineral magnetic signatures proved to be relatively poor discriminators of potential sources, and the high atmospheric
pollution load from the West Midland conurbation has probably altered recent lake sediment signatures. Although further research
is required to identify the origins of recent (last ca. 200 years) minerogenic sediment inputs to the Mere, we suggest that
the combined lake: catchment approach offers a more rigorous method for understanding the impact of catchment disturbance
than analysis of the paleolimnological record alone. 相似文献
995.
996.
Claude Robin Jean-Philippe Eissen Pablo Samaniego Hervé Martin Minard Hall Joseph Cotten 《Bulletin of Volcanology》2009,71(3):233-258
The Mojanda–Fuya Fuya Volcanic Complex consists of two nearby volcanoes, Mojanda and Fuya Fuya. The older one, Mojanda volcano
(0.6 to 0.2 Ma), was first constructed by andesites and high-silica andesites forming a large stratovolcano (Lower Mojanda).
This edifice was capped by a basaltic andesite and andesitic cone (Upper Mojanda), which collapsed later to form a 3-km-wide
summit caldera, after large phreatomagmatic eruptions. The Lower Fuya Fuya edifice was constructed by the extrusion of viscous
Si-rich andesitic lavas and dacitic domes, and the emission of a thick sequence of pyroclastic-flow and fallout deposits which
include two voluminous rhyolitic layers. An intermediate construction phase at Fuya Fuya is represented by a mainly effusive
cone, andesitic in composition (San Bartolo edifice), the construction of which was interrupted by a major sector collapse
in the Late Pleistocene. Finally, a complex of thick siliceous lavas and domes was emplaced within the avalanche amphitheatre,
forming the Upper Fuya Fuya volcanic centre. This paper shows that the general evolution from an effusive to an explosive
eruptive style is related to a progressive adakitic contribution to the magma source. Although all the rocks of the complex
are included in the medium-K field of continental arcs, the Fuya Fuya suite (61–75 wt.% SiO2) shows depletion in Y and HREE and high Sr/Y and La/Yb values, compared to the less silicic Mojanda suite (55–66.5 wt.% SiO2). The Mojanda calc-alkaline suite was generated by partial melting of an adakite-metasomatised mantle source that left a
residue with 2% garnet, followed by fractional crystallization of dominant plagioclase + pyroxene + olivine at shallow, intra-crustal
depths. For Fuya Fuya, geochemical and mineralogical data suggest either (1) partial melting of a similar metasomatised mantle
with more garnet in the residue (4%), followed by fractional crystallization involving plagioclase, amphibole and pyroxene,
or (2) mixing of mafic mantle-derived magma from the Mojanda suite and slab melts, followed by the same fractional crystallization
process. 相似文献
997.
P.W. Webley B.J.B. Stunder K.G. Dean 《Journal of Volcanology and Geothermal Research》2009,186(1-2):108
Ash clouds are one of the major hazards that result from volcanic eruptions. Once an eruption is reported, volcanic ash transport and dispersion (VATD) models are used to forecast the location of the ash cloud. These models require source parameters to describe the ash column for initialization. These parameters include: eruption cloud height and vertical distribution, particle size distribution, and start and end time of the eruption. Further, if downwind concentrations are needed, the eruption mass rate and/or volume of ash need to be known. Upon notification of an eruption, few constraints are typically available on many of these source parameters. Recently, scientists have defined classes of eruption types, each with a set of pre-defined eruption source parameters (ESP). We analyze the August 18, 1992 eruption of the Crater Peak vent at Mount Spurr, Alaska, which is the example case for the Medium Silicic eruption type. We have evaluated the sensitivity of two of the ESP – the grain size distribution (GSD) and the vertical distribution of ash – on the modeled ash cloud. HYSPLIT and Puff VATD models are used to simulate the ash clouds from the different sets of source parameters. We use satellite data, processed through the reverse absorption method, as reference for computing statistics that describe the modeled-to-observed comparison. With the grain size distribution, the three options chosen, (1) an estimated distribution based on past eruption studies, (2) a distribution with finer particles and (3) the National Oceanic and Atmospheric Administration HYSPLIT GSD, have little effect on the modeled ash cloud. For the initial vertical distribution, both linear (uniform concentration throughout the vertical column) and umbrella shapes were chosen. For HYSPLIT, the defined umbrella distribution (no ash below the umbrella), apparently underestimates the lower altitude portions of the ash cloud and as a result has a worse agreement with the satellite detected ash cloud compared to that with the linear vertical distribution for this particular eruption. The Puff model, with a Poisson function to represent the umbrella cloud, gave similar results as for a linear distribution, both having reasonable agreement with the satellite detected cloud. Further sensitivity studies of this eruption, as well as studies using the other source parameters, are needed. 相似文献
998.
Baha Y. Mirghani Kumar G. Mahinthakumar Michael E. Tryby Ranji S. Ranjithan Emily M. Zechman 《Advances in water resources》2009
Groundwater characterization involves the resolution of unknown system characteristics from observation data, and is often classified as an inverse problem. Inverse problems are difficult to solve due to natural ill-posedness and computational intractability. Here we adopt the use of a simulation–optimization approach that couples a numerical pollutant-transport simulation model with evolutionary search algorithms for solution of the inverse problem. In this approach, the numerical transport model is solved iteratively during the evolutionary search. This process can be computationally intensive since several hundreds to thousands of forward model evaluations are typically required for solution. Given the potential computational intractability of such a simulation–optimization approach, parallel computation is employed to ease and enable the solution of such problems. In this paper, several variations of a groundwater source identification problem is examined in terms of solution quality and computational performance. The computational experiments were performed on the TeraGrid cluster available at the National Center for Supercomputing Applications. The results demonstrate the performance of the parallel simulation–optimization approach in terms of solution quality and computational performance. 相似文献
999.
1000.