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排序方式: 共有197条查询结果,搜索用时 15 毫秒
71.
Drying and dying of a subducted slab: Coupled Li and B isotope variations in Western Anatolia Cenozoic Volcanism 总被引:1,自引:0,他引:1
Samuele Agostini Jeffrey G. Ryan Sonia Tonarini Fabrizio Innocenti 《Earth and Planetary Science Letters》2008,272(1-2):139-147
In lavas spanning ~ 10Ma of subduction-related volcanism in Western Anatolia, we observe remarkably similar patterns of δ7Li and δ11B variation. In this setting, magmatism records a transition from calc–alkaline to ultrapotassic character, consistent with overall lower mean extents of melting, and a changing mantle source that reflects a fractionating, higher temperature slab input consistent with the gradual cessation of subduction. Subsequent rift-related intraplate magmatism record δ7Li signatures within the range observed for MORBs and OIBs, indicating an abrupt transition to a mantle source unmodified by subduction. 相似文献
72.
Alfredo Reyes-Salazar José M. Sauceda-Pimentel Sonia E. Ruiz Edén Bojórquez Juan Bojorquez 《Bulletin of Earthquake Engineering》2018,16(11):5557-5590
A numerical investigation regarding the seismic behavior of complex-3D steel buildings with perimeter moment resisting frames (PMRF) and interior gravity frames (GF) is conducted. The interior connections are assumed to be first perfectly pinned (PP) and then semi-rigid (SR); the two model responses are compared. Three steel building models representing low-, medium- and high-rise buildings, and several strong motions are used. The relative stiffness of SR connections is calculated according to the Richard Model and the Beam Line Theory. The Ruaumoko Computer Program is used to perform the required step-by-step nonlinear seismic analysis. Results indicate that interstory shears and interstory displacements at PMRF may be significantly reduced when interior connections are modeled as SR. Average reductions of up to 20, 46 and 11% are observed for interstory shears, for low-, medium-, and high-rise buildings, respectively. The corresponding reductions for interstory displacements are about 14, 44 and 15%. The contribution of GF to the lateral resistance is considerable, which significantly increases when the connections are modeled as SR; relative contributions larger than 80% are observed. The dissipated energy (DE) at PMRF is larger for the buildings with PP than for the buildings with SR connections indicating that damage at PMRF is reduced. Thus, the effect of the stiffness and the DE at interior connections should not be ignored. However, the design of some elements, particularly columns of the GF, has to be revised; these members may not be able to support the loads produced by the neglected lateral contribution if they are not properly designed. 相似文献
73.
Comparison of numerical hindcasted severe waves with Doppler radar measurements in the North Sea 总被引:1,自引:1,他引:0
Severe sea states in the North Sea present a challenge to wave forecasting systems and a threat to offshore installations such as oil and gas platforms and offshore wind farms. Here, we study the ability of a third-generation spectral wave model to reproduce winter sea states in the North Sea. Measured and modeled time series of integral wave parameters and directional wave spectra are compared for a 12-day period in the winter of 2013–2014 when successive severe storms moved across the North Atlantic and the North Sea. Records were obtained from a Doppler radar and wave buoys. The hindcast was performed with the WAVEWATCH III model (Tolman 2014) with high spectral resolution both in frequency and direction. A good general agreement was obtained for integrated parameters, but discrepancies were found to occur in spectral shapes. 相似文献
74.
东印度洋现生浮游有孔虫 总被引:1,自引:0,他引:1
A brief morphometric study of the recent planktonic foraminifera in the eastern Indian Ocean was provided with the taxonomic key to species,synonyms,SEM microphotographs of shells and chamber arrays.By recent classification,currently 20 species representing 13 genera and 6 families(Canderinidae,Heterohelicoidae,Hedbergellidae,Higerigerinoidae,Globigerinoidae,and Globorotaloidae)identified from the planktonic material of the eastern Indian Ocean up to a depth of 200 m.Their distribution in water(0–200 m)also reports on the new range of expansion in the eastern Indian Ocean,with Dentigloborotalia anfracta,Hastigerina pelagica,Streptochilus globigerus,Globigerinella calida,Globigerinella adamsi,Orcadia reidelii,Tenuitella parkerae,Tenuitella compressa,reported for the first time in this study area.In general,only around 50 planktonic species are valid worldwide,more specifically the species,e.g.,H.pelagica,G.calida,G.adamsi,S.globigerus,O.riedeli,T.parkerae,T.compressa,which occur in the eastern Indian Ocean to fill the the paucity of the recent regional taxonomic literature and the problematic identification from the eastern Indian Ocean.This work aims to bridge this gap and help scientists,managers,educators and students to identify plankton foraminifers by using species notes and images. 相似文献
75.
Castro-Correa Carmen-Paz Aldunce Ide Paulina Wyndham Vásquez Katherine Mena Maldonado Dania Pérez Tello Sonia 《Natural Hazards》2020,103(2):2427-2440
Natural Hazards - This article analyzes the impact of socio-natural disasters on social capital at a local level, studying the cases of the communities of Chañaral and Diego de Almagro after... 相似文献
76.
David A Dagnino S Pichot Y Munaron D Escande A Casellas C Fenet H Gomez E 《Marine environmental research》2008,66(1):105-107
In vitro bioassays would facilitate monitoring of estrogen-like compounds in mussels (Mytilus galloprovincialis) since they tend to accumulate lipophilic compounds in their fat and muscle tissue. However, estradiol (E2) steroid (already identified in mussels) could induce false positive responses. This study focuses on temporal variability in estrogenic responses of mussel extracts and the possible relation of this response with E2 levels. The reproductive cycle and growth were thus monitored for six months in sexed mussels. E2 levels were similar between genders and these levels varied with reproductive stages. human estrogen receptor (hER) activities were similar at all stages except in February. E2 present in male and female extracts accounted for part of the hER activation observed, but no correlation was found between E2 levels and hER activities. 相似文献
77.
78.
79.
Quasi-periodic fluctuations in the Greenland–Iceland–Norwegian Seas region in a coupled climate model 总被引:1,自引:1,他引:0
We report an analysis of the mechanisms responsible for interannual variability in the Greenland–Iceland–Norwegian (GIN) Seas
in a control integration of the HadCM3 coupled climate model. Interannual variability in sea surface temperature (SST) and
sea surface salinity (SSS) is dominated by a quasi-periodic ∼7-year signal. Analyses show that the mechanism involves a competition
between convection and advection. Advection carries cold, fresh, Arctic water over warm, salty, Atlantic water, while convection
periodically mixes these two water masses vertically, raising SST. Convection is able to raise SST because of the presence
of a subsurface temperature maximum. The GIN Seas convection in HadCM3 is forced by wind stress anomalies related to the North
Atlantic Oscillation (NAO). The consequent SST anomalies feedback positively to force the atmosphere, resulting in a weak
spectral peak (at ∼7 years) in GIN Seas sea level pressure. Although there is no evidence of a similar oscillation in reality,
key aspects of the simulated mechanism may be relevant to understanding variability in the real GIN Seas. In particular, the
potential for increases in convection to raise SST offers a possible new explanation for increases in SST that occurred between
the 1960s and the late 1980s/early 1990s. These SST increases may have contributed to the observed sea-ice retreat. In addition,
a positive feedback between GIN Seas SST and the atmosphere could contribute to the persistence of the NAO, potentially helping
to explain its red spectrum or recent northeastward shift.
相似文献
Sonia R. Gamiz-FortisEmail: |
80.
Stratigraphy,age and petrography of the Beni Issef successions (External Rif; Morocco): Insights for the evolution of the Maghrebian Chain 总被引:1,自引:0,他引:1
Angelida Di Staso Vincenzo Perrone Sonia Perrotta Mohamed Najib Zaghloul Michel Durand-Delga 《Comptes Rendus Geoscience》2010,342(9):718-730
In the Beni Issef Massif, nearly 30 km west of Chefchaouen (Morocco), the thickest post-nappe succession within the Rifian sector of the Maghrebian Chain seals the tectonic contact between the Intrarifian External Tanger and Loukkos Units, related to the Rifian External Domain. This succession is very important for the reconstruction of the deformation timing of the Rifian Maghrebids. The age of its base, in fact, is an important constraint for defining an upper boundary to the stacking of both the Intrarifian and Maghrebian Flysch Basin Units, because clasts fed by the Melloussa and Numidian Flysch Nappes are abundant in the conglomerate layers. Field and biostratigraphic analyses pointed out the presence of a Lower Beni Issef Fm, unconformable on the Intrarifian External Tanger and Loukkos Units, and an Upper Beni Issef Fm, unconformable on both the Intrarifian Units and the Lower Beni Issef Fm. The Lower Beni Issef Fm, 150 m thick, consists of lenticular conglomerates with huge blocks in a marly-clayey matrix, followed by marls and minor sandstones. It deposited in a siliciclastic platform, shows a fining upward trend and is affected by metre- to hectometre-sized, locally reversed, folds. Samples collected 45–50 m above the base of the formation resulted not older than Late Tortonian in age, but an older age for the base of the formation cannot be excluded. The Upper Beni Issef Fm, up to 550 m thick, starts with coarse conglomerates followed by medium- to coarse-grained well-bedded sandstones and by grey-blue marls and mudrocks. It indicates deposition in a channelized marine delta, with evolution towards pro-delta pelites, and shows sub-horizontal or gently dipping beds towards the east. Biostratigraphic data indicate a probable Messinian age for this formation. The composition of the arenites of both Lower Beni Issef and Upper Beni Issef Fms is quartzolithic and all samples show a notable content of monocrystalline well-rounded quartz and sedimentary lithic fragments. Detrital modes, all falling in the Quartzose Recycled and Transitional Recycled fields, suggest a provenance from recycling of sedimentary successions, easily recognizable in the Flysch Basin and External Units, mainly the Numidian Nappe sandstones. A Tortonian age of the Lower Beni Issef Fm would agree with the Late Serravallian age of the uppermost beds of the External Tanger Unit and indicate that the most probable age for the stacking of the Intrarifian Units falls in the Late Serravallian-Middle Tortonian time span. The Lower Beni Issef Fm was involved in a compressive tectonic phase testified by north-south striking folds. Later, probably during Messinian, the Upper Beni Issef Fm deposited in a younger intramontane basin, resting on both the Intrarifian Units and the Lower Beni Issef Fm. Successively, the Upper Beni Issef Fm was passively transported piggyback on top of the fold and thrust belt during later tectonic evolution of the Rifian Maghrebids. This tectonic evolution results quite similar to that recognized in the Tellian and Sicilian Maghrebids and also in the southern Apennines. 相似文献