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941.
Evidence for mid- to late-Holocene palaeotsunami deposits,Kakawis Lake,Vancouver Island,British Columbia 总被引:1,自引:1,他引:0
Gloria I. López 《Natural Hazards》2012,60(1):43-68
Kakawis Lake situated four metres above sea level on western Vancouver Island, British Columbia, Canada, was the target of
a palaeotsunami investigation. Six percussion cores recovered from this lake contain six anomalous deposits interbedded within
the unconsolidated lacustrine sediments. Detailed sedimentological, geophysical and macro-fraction analyses were performed.
The methods new to palaeoseismic approaches proved to be successful tools to characterize the anomalously coarse layers enriched
in terrestrial plant detritus and marine shells. Based on at least eight types of evidence, six tsunami inundations are suggested
as mechanisms responsible for the anomalous deposition, spanning from 3,634 to 2,534 cal yrs BP. Each tsunami event consists
of a combination of different lithological facies resulting from different stages of tsunami inundation and settling of the
material in the lake basin (pulses and inter-pulses). Tsunami deposits in lakes are shown to be less vulnerable to erosional
and bioturbation processes than those found in marshes or beaches as well as underwater marine environments. However, few
palaeoseismic studies have been carried out in low-elevation lakes along the Cascadia Subduction Zone region. The three last
tsunami events known to have inundated areas along the Pacific shores of southern British Columbia, Canada and northern USA
are not present at Kakawis Lake, establishing a current <4 m above mean sea level vertical limit as possible maximum tsunami
height for areas located away from fjord heads on Vancouver Island. The anomalous deposits found in Kakawis Lake may be the
oldest geological evidence of inferred tsunami on Vancouver Island, providing a possible recurrence interval between 200 and
400 years. 相似文献
942.
Kyounghee Yang Csaba Szabó Shoji Arai Jae-Eun Yu Hoonyeong Jung 《Mineralogy and Petrology》2012,106(1-2):107-130
Group II xenoliths, corresponding to the lithology of dunite, wehrlite to olivine clinopyroxenite and olivine websterite to websterite, occur in Pleisto-Holocene alkali basalts from Jeju Island, South Korea. The large grain size (up to 5?mm), moderate mg# [=100?×?Mg/(Mg?+?Fetotal) atomic ratio] of olivine (79–82) and pyroxenes (77–83), and absence of metamorphic textural features indicate that they are cumulates of igneous origin. Based on textural features, mineral equilibria and major and trace element variations, it can be inferred that the studied xenoliths were crystallized from basaltic melts enriched in incompatible trace elements and belong to the Jeju Pleisto-Holocene magma system. They appear to have been emplaced near the present Moho, an estimated 5–8?kbars beneath Jeju Island. Consolidation of cumulates was followed by infiltration of silica-enriched metasomatic melt, producing secondary orthopyroxenes at the expense of olivine. The metasomatic agent appears to have been a silica-enriched residual melt evolved from an initially slightly silica-undersaturated alkali basalt to silica-saturated compositions by fractional crystallization under relatively high pressure conditions. The result of this study indicates that relatively young olivine-bearing cumulates could have been metasomatized by a silica-enriched melt within underplates, suggesting that silica enrichment can occur in intraplate Moho-related rocks as well as in the upper mantle of the subarc area. 相似文献
943.
Tibor?GuzmicsEmail author Roger?H.?Mitchell Csaba?SzabóEmail author Márta?Berkesi Ralf?Milke Kitti?Ratter 《Contributions to Mineralogy and Petrology》2012,164(1):101-122
The evolution of a carbonated nephelinitic magma can be followed by the study of a statistically significant number of melt inclusions, entrapped in co-precipitated perovskite, nepheline and magnetite in a clinopyroxene- and nepheline-rich rock (afrikandite) from Kerimasi volcano (Tanzania). Temperatures are estimated to be 1,100°C for the early stage of the melt evolution of the magma, which formed the rock. During evolution, the magma became enriched in CaO, depleted in SiO2 and Al2O3, resulting in immiscibility at ~1,050°C and crustal pressures (0.5–1 GPa) with the formation of three fluid-saturated melts: an alkali- and MgO-bearing, CaO- and FeO-rich silicate melt; an alkali- and F-bearing, CaO- and P2O5-rich carbonate melt; and a Cu–Fe sulfide melt. The sulfide and the carbonate melt could be physically separated from their silicate parent and form a Cu–Fe–S ore and a carbonatite rock. The separated carbonate melt could initially crystallize calciocarbonatite and ultimately become alkali rich in composition and similar to natrocarbonatite, demonstrating an evolution from nephelinite to natrocarbonatite through Ca-rich carbonatite magma. The distribution of major elements between perovskite-hosted coexisting immiscible silicate and carbonate melts shows strong partitioning of Ca, P and F relative to FeT, Si, Al, Mn, Ti and Mg in the carbonate melt, suggesting that immiscibility occurred at crustal pressures and plays a significant role in explaining the dominance of calciocarbonatites (sövites) relative to dolomitic or sideritic carbonatites. Our data suggest that Cu–Fe–S compositions are characteristic of immiscible sulfide melts originating from the parental silicate melts of alkaline silicate–carbonatite complexes. 相似文献
944.
José António Crispim 《Geodinamica Acta》2013,26(3-4):135-142
AbstractDistinctions between cave morphologies originating from seismic or active tectonics and those generated by natural clastic breakdown or by human activity must be made using unambiguous interpretative criteria.Easily accessible caves in particular, which may have been visited for centuries or millennia, or caves located near engineering works or quarries using great quantities of explosives, may have broken speleothems, breakdowns or detachment joints unrelated to seismic events or tectonic movements.Zambujal cave lies near neotectonic and seismic structures associated with a Plio-Quatemary 200 m uplift of the Arrábida chain and has suffered impacts resulting from quarrying, followed by possible vandalism. It is thus an example for which it is difficult to decipher morphological agents as there is the possibility that identical forms have been generated by several causes, which may have repeated at different episodes of its evolution. However, a careful morphological interpretation makes it possible to accept the existence of two seismic episodes, an “ancient” one and a “modern” one. The detection of other episodes between these is only possible using absolute dating. © Elsevier, Paris 相似文献
945.
Rift zones at the divergent plate boundary in Iceland consist of central volcanoes with swarms of fractures and fissures extending
away from them. Fissure swarms can display different characteristics, in accordance with their locations within the ∼50-km-wide
rift zones. To better discern the characteristics of fissure swarms, we mapped tectonic fractures and volcanic fissures within
the Kverkfj?ll volcanic system, which is located in the easternmost part of the Northern Volcanic Rift Zone (NVZ). To do this,
we used aerial photographs and satellite images. We find that rifting structures such as tectonic fractures, Holocene volcanic
fissures, and hyaloclastite ridges are unevenly distributed in the easternmost part of the NVZ. The Kverkfj?ll fissure swarm
extends 60 km north of the Kverkfj?ll central volcano. Holocene volcanic fissures are only found within 20 km from the volcano.
The Fjallgarear area, extending north of the Kverkfj?ll fissure swarm, is characterized by narrow hyaloclastite ridges indicating
subglacial volcanism. We suggest that the lack of fractures and Holocene volcanic fissures there indicates decreasing activity
towards the north in the easternmost part of the NVZ, due to increasing distance from the long-term spreading axis. We argue
that arcuate hyaloclastite ridges at the eastern boundary of the Northern Volcanic Rift Zone are mainly formed during deglaciations,
when three conditions may occur; firstly, eruption rate increases due to decompression of the mantle. Secondly, the high tensile
stresses accumulated during glaciations due to lack of magma supply may be relieved as magma supply increases during deglaciations.
Thirdly, faulting may occur during unloading due to differential movements between the thinner and younger Northern Volcanic
Rift Zone crust and the thicker and older crust to the east of it. 相似文献
946.
947.
Jorge Proen?a António Sousa Gago Joaquim Cardoso Vítor Cóias Raquel Paula 《Bulletin of Earthquake Engineering》2012,10(1):113-133
Traditional non-reinforced masonry walls are particularly prone to failure when subjected to out-of-plane loads and displacements
caused by earthquakes. Moreover, singularities such as openings in fa?ades may trigger local collapse, for either in-plane
or out-of plane motion. Bearing in mind all the former limitations, STAP, with the scientific support of ICIST and LNEC, has
been developing a reduced intrusiveness seismic strengthening methodology for traditional masonry structures. The technique
consists in externally applying Glass Fibre Reinforced Polymer (GFRP) composite strips to one or both faces of walls. Connection
between GFRP composite strips and masonry substrate is enhanced through specifically detailed anchorages or confinement connectors.
This technique has been developed and studied through an extensive series of experimental tests, which are briefly reviewed.
This paper focuses more deeply on the latest experimental program, aimed at the characterization of the masonry-GFRP composite
interface behaviour. This testing program comprised 29 masonry specimens, strengthened with externally bonded GFRP composite
strips with anchorages. The testing variables were the number and spacing of anchorages as well as the loading history type:
monotonic or repeated. Results clearly show that the use of anchorages dramatically enhances bond behaviour and that its number
and spacing have a significant effect on deformation capacity and a less pronounced effect on strength. Based on experimental
evidence, this paper also provides a calculation model and ULS safety assessment procedure for out-of-plane strength of reinforced
masonry walls. This calculation model leads to interaction curves on strengthened masonry walls subjected to compression and
out-of-plane flexure. 相似文献
948.
Bruno Silva Jo?o M. Guedes António Arêde Aníbal Costa 《Bulletin of Earthquake Engineering》2012,10(1):211-234
The conservation and rehabilitation of monuments is a matter of important investigation, and the need for accurate structural
analysis, capable of effectively predicting the structural behaviour of this type of constructions, under static and dynamic
loads, is increasing. Currently there are numerous computational methods and tools, supported by different theories and strategies
with different levels of complexity, computation time and cost which are available to perform such analyses. A complex analysis
is not always synonym of a better result and the choice of a method over another depends mostly on the purpose of the analysis.
This work aims at evaluating the capacity of a non linear continuum damage model (Faria et al. in Int J Solids Struct 35(14):1533–1558,
1998), originally developed for concrete structures, to simulate the behaviour of stone masonry structures. In particular, the
seismic response of an old stone masonry construction, the Gondar church, is analysed considering different levels of geometrical
and material complexity. The verification and calibration procedures use the experimental results from tests performed on
stone masonry walls at the Laboratory for Earthquake and Structural Engineering of the Faculty of Engineering of Porto University
and from other tests found in the bibliography (Vasconcelos in Experimental investigations on the mechanics of stone masonry:
Characterization of granites and behaviour of ancient masonry shear walls. PhD Thesis, Universidade do Minho, Guimar?es, Portugal,
2005). The results are compared, assessing the differences and the importance of using complex tools, such as the continuum damage
model, to better simulate and understand the global behaviour of such constructions. 相似文献
949.
The performance of different nonlinear modelling strategies to simulate the response of RC columns subjected to axial load combined with cyclic biaxial horizontal loading is compared. The models studied are classified into two categories according to the nonlinearity distribution assumed in the elements: lumped-plasticity and distributed inelasticity. For this study, results of tests on 24 columns subjected to cyclic uniaxial and biaxial lateral displacements were numerically reproduced. The analyses show that the global envelope response is satisfactorily represented with the three modelling strategies, but significant differences were found in the strength degradation for higher drift demands and energy dissipation. 相似文献
950.
The performance of one pilot‐scale and two full‐scale membrane bioreactors (MBR) were evaluated based on the control of main operational parameters, composition of microbial community and pathogens concentration in the treated outlet. Plants were designed for 0.75 m3/day (A), 60 m3/day (B) and 30 m3/day (C). Inlet and outlet samples were monitored for chemical oxygen demand (COD), biological oxygen demand, total suspended solids, ammonia nitrogen concentration (NH4–N), nitrate nitrogen concentration, total Kjeldahl nitrogen, total phosphorus and phosphate phosphorus concentration concentrations. Plants showed good COD removal: 91.9% for Plant A, 97.8% for Plant B and 94.2% for Plant C. The targeted nitrogenous ion was NH4–N due to the requirements for outlet limits. NH4–N removal was moderate for Plant A (73.3%) and Plant B (86.1%) and excellent for Plant C (>99%). Excellent phosphorus removal was achieved by Plant A (average outlet concentration was 0.7 mg/L, efficiency 84.7%). Unsatisfactory results for phosphorus removal were achieved at the full‐scale plants due to operational problems. The dependency between the extracellular polymeric substances increase and decreasing mixed liquor volatile suspended solids for both lab and full‐scale plants was confirmed. Soluble microbial product concentrations were reduced by 65–68% after coagulant dosage for Plant A. Outlets from the MBR plants were monitored for the presence of pathogens (thermotolerant coliforms, Escherichia coli, intestinal Enterococci and culturable microorganisms at 22 and 37°C). The treated effluent from Plant A, B and C met Czech national legislation regarding reuse criteria (standards) for environment, irrigation and swimming purposes. Plants B and C were not able to achieve requirements for potable water and personal hygiene quality standards. 相似文献