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311.
T. Boldizsár 《Pure and Applied Geophysics》1970,80(1):260-266
Summary Although active volcanic territories are not characterised by extreme high heat flow, yet terrestrial heat is one of the main, if not hte first cause of volcanic activities. About 94 per cent of the known active volcanoes are in connection with orogenic zones including ocean ridges, which mean that processes responsible for the evolution of the continents cause the overwhelming majority of volcanism.There stages of the evolution of the continental crust can be distinguished: 1.) Growth of the continental cores by differentiation, 2.) Existence of peripheral growing zones around the first core, 3.) Intergrowth of the existing continents.Volcanism, as well as seismicity are manifestations of the evolution of the crust which is caused by the development of heat sources in the mantle. The heat partly melt the upper mantle and induce slow plastic flow in connection of differentiation. The space, left empty by continental uplift is filled by the slow plastic inflow of mantle from the ocean. This slow redistribution of mantle and curstal rocks disturbs the stress field, the rocks fail along the strained zones and zones of fractures appear sometimes with volcanic activity. 相似文献
312.
313.
R. T. Helz 《Bulletin of Volcanology》1980,43(4):675-701
Kilauea Iki lava lake formed during the 1959 summit eruption, one of the most picritic eruptions of Kilauea Volcano in the twentieth century. Since 1959 the 110 to 122 m thick lake has cooled slowly, developing steadily thickening upper and lower crusts, with a lens of more molten lava in between. Recent coring dates, with maximum depths reached in the center of the lake, are: 1967 (26.5 m). 1975 (44.2 m), 1976 (46.0 m) and 1979 (52.7 m). These depths define the base of the upper crust at the time of drilling. The bulk of the core consists of a gray, olivine-phyric basalt matrix, which locally contains coarser-grained diabasic segregation veins. The most important megascopic variation in the matrix rock is its variation in olivine content. The upper 15 m of crust is very olivine-rich. Abundance and average size of olivine decrease irregularly downward to 23 m; between 23 and 40 m the rock contains 5–10% of small olivine phenocrysts. Below 40 m. olivine content and average grainsize rise sharply. Olivine contents remain high (20–45%, by volume) throughout the lower crust, except for a narrow (< 6 m) olivine depleted zone near the basalt contact. Petrographically the olivine phenocrysts in Kilauea Iki can be divided into two types. Type 1 phenocrysts are large (1–12 mm long), with irregular blocky outlines, and often contain kink bands. Type 2 crystals are relatively small (0.5–2 mm in length), euhedral and undeformed. The variations in olivine content of the matrix rock are almost entirely variations in the amount of type 1 olivines. Sharp mineral layering of any sort is rare in Kilauea Iki. However, the depth range 41–52 m is marked by the frequent occurrence of steeply dipping (70°–90°) bands or bodies of slightly vuggy olivine-rich rock locally capped with a small cupola of segregation-vein material. In thin section there is clear evidence for relative movement of melt and crystals within these structures. The segregation veins occur only in the upper crust. The most widely distributed (occurring from 4.5–59.4 m) are thin veins (most < 5 cm thick), which cut the core at moderate angles and appear to have been derived from the immediately adjacent wall-rock by filter pressing. There is also a series of thicker (0.1–1.5 m) segregation veins, which recur every 2–3 m, between 20 and 52 m. These have subhorizontal contacts and appear, from similarities in thickness and spacing, to correlate between drill holes as much as 100 m apart. These large veins are not derived from the adjacent wallrock: their mechanism of formation is still problematical. The total thickness of segregation veins in Kilauea Iki is 3–6 m in the central part of the lake, corresponding to 6–11% of the upper crust. Whole-rock compositions for Kilauea Iki fall into two groups: the matrix rock ranges from 20-7.5% MgO, while the segregation veins all contain between 6.0 and 4.5% MgO. There are no whole-rock compositions of intermediate MgO content. Samples from < 12 m show eruption-controlled chemistry. Below that depth, matrix rock compositions have higher Al2O3, TiO2 and alkalies, and lower CaO and FeO, at a given MgO content than do the eruption pumices. The probable causes of this are assimilation of low-melting components from foundered crust, plus removal of olivine, plus removal of minor augite, for rocks with MgO contents of < 8.0%. Given the observed rate of growth of the upper crust, one can infer that significant removal of the type 1 olivine phenocrysts from the upper part of the lake began in 1963 and ceased sometime prior to 1972. The process. probably gravitative settling, appears to have been inhibited earlier by gas streaming from the lower part of the lens of melt. The olivine cumulate zone, which extends into the upper crust, contains relatively few (25–40%) olivine crystals, few of which actually touch each other. The diffuseness of the cumulate zone raises the possibility that the crystals were coated with a relatively visous boundary layer of melt which moved with them. Calculations of the Stokes’ law settling rates of the largest olivine crystals found at the base of the crust in 1975–76 suggest that the «melt» had a viscosity of > 106 poises, and probably had the properties of a Bingham body, rather than a Newtonian fluid, by that date, which was several years after olivine removal ceased. 相似文献
314.
Darryll T. Pederson 《Ground water》1979,17(6):604-607
Abstract. This investigation was to determine whether data on irrigation-well registration forms as reported by well drillers can be used in hydrologic studies. Transmissivity maps were prepared for Hamilton County, Nebraska using only specific capacity values computed from yield and drawdown data, as reported on irrigation well-registration forms. On one map each control point was the mean of the transmissivity values calculated for all wells in a section. On a second map each control point was the mean of the means for four contiguous sections sharing a common corner. The second map was similar to that of a previously prepared map based on control point values computed from specific capacities of selected wells, test hole logs, and geologic interpretations. These results suggest that reported registration data for a given area have a normal population distribution. In situations where individual data are unverified the data base can be treated as samples of a population where the mean of the means of several samples for adjacent areas is representative of actual field conditions. 相似文献
315.
A reservoir of water is contained by a concrete valley block, a ferrocement wall and a steel plate. Both wall and plate contain an array of pressure transducer sockets (Figures 1 and 2). Using the M.A.M.A.1 equipment pure modes of vibration are excited. Frequency and mode shape are measured with the reservoir empty. When the reservoir is full hydrodynamic pressure is also measured. These hydrodynamic pressures are compared with Chopra's2 two-dimensional, series solution, which includes compressibility of water, and with two- and three-dimensional finite element solutions of Laplace's equation, which do not include compressibility. Chopra's solution is unsatisfactory for modes which contain a vertical node line. The best agreement between experimental and theoretical hydrodynamic pressure is obtained when the latter is obtained from three-dimensional solutions of Laplace's equations, indicating that compressibility does not play a significant rǒle. This conclusion is supported by agreement between experimental frequencies (reservoir full) and those calculated using added mass obtained from the Laplace solution. Similar conclusions were reached from tests on a floating steel plate, suspended in the surface of the reservoir by a soft spring. Here, dynamic pressure measurements were not made, reliance being placed on agreement between calculated and measured frequencies and mode shapes. 相似文献
316.
317.
Iunio Iervolino Carmine Galasso Edoardo Cosenza 《Bulletin of Earthquake Engineering》2010,8(2):339-362
In code-based seismic design and assessment it is often allowed the use of real records as an input for nonlinear dynamic
analysis. On the other hand, international seismic guidelines, concerning this issue, have been found hardly applicable by
practitioners. This is related to both the difficulty in rationally relating the ground motions to the hazard at the site
and the required selection criteria, which do not favor the use of real records, but rather various types of spectrum matching
signals. To overcome some of these obstacles a software tool for code-based real records selection was developed. REXEL, freely
available at the website of the Italian network of earthquake engineering university labs (), allows to search for suites of waveforms, currently from the European Strong-motion Database, compatible to reference spectra
being either user-defined or automatically generated according to Eurocode 8 and the recently released new Italian seismic
code. The selection reflects the provisions of the considered codes and others found to be important by recent research on
the topic. In the paper, record selection criteria are briefly reviewed first, and then the algorithms implemented in the
software are discussed. Finally, via some examples, it is shown how REXEL can effectively be a contribution to code-based
real records selection for seismic structural analysis. 相似文献
318.
Giuseppe D. Chirico Massimiliano Favalli Paolo Papale Enzo Boschi Maria Teresa Pareschi Arthur Mamou-Mani 《Bulletin of Volcanology》2009,71(4):375-387
Mt. Nyiragongo is one of the most dangerous volcanoes in the world for the risk associated with the propagation of lava flows.
In 2002 several vents opened along a huge system of fractures, pouring out lava which reached and destroyed a considerable
part of Goma, a town of about 500,000 inhabitants on the shore of Lake Kivu. In a companion paper (Favalli et al. in Bull
Volcanol, this issue, 2008) we employed numerical simulations of probable lava flow paths to evaluate the lava flow hazard on the flanks of the volcano,
including the neighbouring towns of Goma (DRC) and Gisenyi (Rwanda). In this paper we use numerical simulations to investigate
the possibility of significantly reducing the lava flow hazard in the city through the construction of protective barriers.
These barriers are added to the DEM of the area as additional morphological elements, and their effect is evaluated by repeating
numerical simulations with and without the presence of barriers. A parametric study on barrier location, size, shape and orientation
led to the identification of barriers which maximize protection while minimizing their impact. This study shows that the highest
hazard area corresponding to eastern Goma, which was largely destroyed by lava flows in 2002, cannot be effectively protected
from future lava flows towards Lake Kivu and should be abandoned. On the contrary, the rest of the town can be sheltered from
lava flows by means of two barriers that deviate or contain the lava within the East Goma sector. A proposal for the future
development of the town is formulated, whereby “new” Goma is completely safe from the arrival of lava flows originating from
vents outside its boundaries. The proposal minimizes the risk of further destruction in town due to future lava flows. 相似文献
319.
The seasonal nature of Australia’s tropical rivers means that connected groundwater aquifers are an important source of both
consumptive and non-consumptive water, particularly during the dry season. The management of these common pool groundwater
resources is one of the predominant water issues facing northern Australia. A national program of water reform stipulates
the expansion of water trading as a key instrument for water allocation. The effectiveness of new institutional arrangements
such as water markets will be determined mostly by how well they coordinate with local environmental requirements, local institutions
and local norms. This paper describes a novel application of combined field work, institutional analysis, experimental economics
and agent-based modeling to the analysis of a potential water market in the Katherine region of the Northern Territory, Australia.
The effectiveness of different versions of the policy instrument is assessed in light of local conditions. Instruments that
enable personal relationships and local institutions and norms to play a role in water management are found to be more effective
in terms of both farming income and environmental impact. 相似文献
320.
Paul R. Renne Alan L. Deino Willis E. Hames Matthew T. Heizler Sidney R. Hemming Kip V. Hodges Anthony A.P. Koppers Darren F. Mark Leah E. Morgan David Phillips Brad S. Singer Brent D. Turrin Igor M. Villa Mike Villeneuve Jan R. Wijbrans 《Quaternary Geochronology》2009,4(5):346-352
Data reported in 40Ar/39Ar geochronology studies are commonly insufficient to allow computation of ages. This deficiency renders it difficult to compare ages based on different standards or constants, and often hinders critical evaluation of the results. Herein are presented an enumeration of the data that should be reported in all 40Ar/39Ar studies, including a discussion in support of these requirements. The minimum required data are identified and distinguished from parameters that are useful but may be derived from them by calculation. Finally, recommendations are made for metadata needed to document age calculations (e.g., from age spectrum or isochron analyses). 相似文献