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331.
In relation to the assessment of earthquake-induced landslide hazard, this paper discusses general principles and describes
implementation criteria for seismic hazard estimates in landslide-prone regions. These criteria were worked out during the
preparation of a hazard map belonging to the official Italian geological cartography and they are proposed as guidelines for
future compilation of similar maps. In the presented case study, we used a procedure for the assessment of seismic hazard
impact on slope stability adopting Arias intensity Ia as seismic shaking parameter and critical acceleration a
c
as parameter representing slope strength to failures induced by seismic shaking. According to this procedure, after a preliminary
comparison of estimated historical maximum values of Ia with values proposed in literature as landslide-triggering thresholds, a probabilistic approach, based on the Newmark’s model,
is adopted: it allows to estimate the minimum critical acceleration a
c
required for a slope to keep under a prefixed value, the probability of failures induced by seismic shakings expected in
a given time interval. In this way, one can prepare seismic hazard maps where seismic shaking is expressed in an indirect
way through a parameter (the critical acceleration) representing the “strength” that seismic shakings mobilise in slope materials
(strength demand) with a prefixed exceedance probability. This approach was applied to an area of Daunia (Apulia—southern
Italy) affected by frequent landslide phenomena. The obtained results indicate that shakings with a significant slope destabilisation
potential can be expected particularly in the north-western part of the area, which is exposed to the seismic activity of
Apennine tectonic structures. 相似文献
332.
333.
Jose Antonio de‐la‐Ossa‐Carretero Yoana Del‐Pilar‐Ruso Francisca Giménez‐Casalduero José Luis Sánchez‐Lizaso 《Marine Ecology》2016,37(3):503-517
The distribution and composition of Amphipoda assemblages were analysed off the coasts of Alicante (Spain, Western Mediterranean), a disturbed area affected by several co‐occurring anthropogenic impacts. Although differences among sampled stations were mainly related to natural parameters, anthropogenic activities were linked with changes in amphipod assemblages. Expansion of the Port of Alicante, a sewage outfall and a high salinity brine discharge could be causing the disappearance of amphipods at stations closer to these disturbances. However, the completion of port enlargement works and mitigatory dilution of the brine discharge has led to the recovery of the amphipod assemblage. Among the natural parameters, depth determines the distribution of some of the species. While Siphonoecetes sabatieri was abundant at shallow stations, Ampelisca spp., Photis longipes, Pseudolirius kroyeri, Apherusa chiereghinii and Phtisica marina were more abundant at deeper stations. Grain size and percentage of organic matter also influenced amphipod distribution, resulting in changes in species composition and in the relative percentages of different trophic groups. Species such as Ampelisca brevicornis, Perioculodes longimanus, Urothoe hesperiae and Urothoe elegans were more abundant at stations with a high content of fine sand. Carnivorous species, mainly of the Oedicerotidae family, were more abundant at those stations with a low organic matter content, while detritivorous species were more abundant at stations with a higher mud content. Among 62 identified species, three were reported for the first time from the Spanish Mediterranean coast, two species were recorded for the second time and a new species of Siphonoecetes was found, Siphonoecetes (Centraloecetes) bulborostrum. These results confirm the need for further data on amphipods from the Mediterranean Spanish coast. 相似文献
334.
T. Belloni I. Parolin M. Del Santo J. Homan P. Casella R. P. Fender W. H. G. Lewin M. Méndez J. M. Miller M. van der Klis 《Monthly notices of the Royal Astronomical Society》2006,367(3):1113-1120
On 2004 August 15, we observed a fast (shorter than 10 h) state transition in the bright black hole transient GX 339–4 simultaneously with Rossi X-Ray Timing Explorer ( RXTE ) and INTEGRAL . This transition was evident both in timing and spectral properties. Combining the data from the Proportional Counter Array (PCA), the High-Energy X-ray Timing Experiment (HEXTE) and the Imager on Board the INTEGRAL Satellite (IBIS), we obtained good quality broad-band (3–200 keV) energy spectra before and after the transition. These spectra indicate that the hard component steepened. Also, the high-energy cut-off that was present at ∼70 keV before the transition was not detected after the transition. This is the first time that an accurate determination of the broad-band spectrum across such a transition has been measured on a short time-scale. It shows that, although some spectral parameters do not change abruptly through the transition, the high-energy cut-off increases/disappears rather fast. These results constitute a benchmark on which to test theoretical models for the production of the hard component in these systems. 相似文献
335.
H. S. Hudson T. N. Woods P. C. Chamberlin L. Fletcher G. Del Zanna L. Didkovsky N. Labrosse D. Graham 《Solar physics》2011,273(1):69-80
The Extreme-ultraviolet Variability Experiment (EVE; see Woods et al., 2009) obtains continuous EUV spectra of the Sun viewed as a star. Its primary objective is the characterization of solar
spectral irradiance, but its sensitivity and stability make it extremely interesting for observations of variability on time
scales down to the limit imposed by its basic 10 s sample interval. In this paper we characterize the Doppler sensitivity
of the EVE data. We find that the 30.4 nm line of He ii has a random Doppler error below 0.001 nm (1 pm, better than 10 km s−1 as a redshift), with ample stability to detect the orbital motion of its satellite, the Solar Dynamics Observatory (SDO). Solar flares also displace the spectrum, both because of Doppler shifts and because of EVE’s optical layout, which
(as with a slitless spectrograph) confuses position and wavelength. As a flare develops, the centroid of the line displays
variations that reflect Doppler shifts and therefore flare dynamics. For the impulsive phase of the flare SOL2010-06-12, we
find the line centroid to have a redshift of 16.8 ± 5.9 km s−1 relative to that of the flare gradual phase (statistical errors only). We find also that high-temperature lines, such as
Fe xxiv 19.2 nm, have well-determined Doppler components for major flares, with decreasing apparent blueshifts as expected from chromospheric
evaporation flows. 相似文献
336.
Silvio Mollo Pierdomenico Del Gaudio Guido Ventura Gianluca Iezzi Piergiorgio Scarlato 《Lithos》2010,118(3-4):302-312
The compositional variation of clinopyroxene and the partitioning of major elements between clinopyroxene and melt are estimated as a function of the cooling rate. Clinopyroxenes were crystallized under variable cooling regimes (15, 9.4, 3, 2.1, and 0.5 °C/min from 1250 down to 1000 °C) and at isothermal conditions of 1000 °C from a basaltic composition at a pressure of 500 MPa under anhydrous and hydrous (H2O = 1.3 wt.%) conditions. The clinopyroxene chemistry shows that, as the cooling rate increases, crystals are progressively depleted in Ca, Mg, Fe2+ and Si and enriched in Na, Fe3+, Al (mainly AlIV), and Ti. Di and Hd versus CaTs and CaFeTs form a continuous binary solid solution characterized by higher amounts of tschermakitic components with increasing cooling rate. Two parameters (DH = Di + Hd and TE = CaTs + CaFeTs + En) are calculated to describe the effect of cooling rate on the clinopyroxene composition. The variation of DH/TE with increasing cooling rate evidences the kinetic process induced by rapid cooling in basic rocks under hydrous and anhydrous conditions.Dynamic crystallization conditions affect the partitioning of major elements between clinopyroxene and melt; with increasing cooling rate, the value of crystal–melt partition coefficient departs from that obtained at the isothermal condition. However, in spite of these variations, the values of cpx–meltKdFe–Mg remain almost constant. Therefore, the Fe2–Mg exchange between clinopyroxene and melt is not suitable to prove the (dis)equilibrium conditions in basaltic cooling magmas, giving rise to possible mismatches in the application of thermobarometers. The results of our study are consistent with that observed at the margin of dikes or in the exterior portions of lavas, where the cooling rate is maximized and disequilibrium compositions of clinopyroxene have been found. 相似文献
337.
Influence of transient storage on stream nutrient uptake based on substrata manipulation 总被引:3,自引:0,他引:3
Alba Argerich Eugènia Martí Francesc Sabater Roy Haggerty Miquel Ribot 《Aquatic Sciences - Research Across Boundaries》2011,73(3):365-376
Quantification of the transient storage zone (As) has become critical in stream biogeochemical studies addressed to examine factors controlling nutrient uptake. It is expected
that higher As may enhance the interaction between nutrients and biota and thus, increase nutrient uptake. However, results from the literature
are controversial. We hypothesized that besides of the size of As, the intrinsic physical and biological characteristics of stream structures that generate As are also relevant for nutrient uptake. We performed 24 additions of phosphate, ammonium, and chloride in four reaches of
a man-made channel where we introduced three types of naturally colonized substrata packs (mud, sand and cobbles) to modify
As. We estimated ammonium and phosphate uptake coefficients in both the main channel and As using a solute transport model (OTIS-P) and compared the results among reaches with different substrata types. The introduction
of substrata packs decreased water velocity and increased As similarly among treatments. Nutrient uptake coefficients in the main channel were similar among reaches with different type
substrata packs; however, nutrient uptake coefficients measured in As differed among them as well as the ratio between ammonium and phosphorus uptake coefficients in As, which were 1.6 in reaches with mud packs and 0.02 in reaches with sand or cobble packs. Results obtained in this study suggest
that the contribution of As in nutrient uptake not only depends on the size of As but on the type of materials used to increase As, and thus, have biogeochemical implications on restoration projects aimed to modify channel morphology. 相似文献
338.
The thermal and exhumation history of late Hercynian granitoids from Calabria (Sila and Serre massifs) has been studied using thermobarometry and radiometric age determinations. The uplift and erosion which followed contractional tectonics of Tertiary age exposed in Calabria a nearly complete section of the Hercynian crust. Field data, constrained by igneous thermobarometrical data, have enabled us to draw simplified crustal profiles. In both the Sila and Serre massifs, granitoids make up the intermediate portions of the crustal sections and are stacked as tabular intrusions for up to 13 km cumulative thickness. Shallow granitoids are characterized by a weak fabric, mostly developed in the magmatic stage, whereas deep‐seated granitoids display a strong fabric developed in the magmatic state and, with decreasing temperatures, in the subsolidus state. The intrusive bodies were emplaced at 300–290 Ma, at a time when the Calabrian crust was undergoing extensional tectonics and crustal thinning. The subsequent post‐Hercynian evolution is recorded by Rb‐Sr dates of micas and fission track ages of zircon and apatite obtained from granitoids emplaced at different depths. A decrease in Rb‐Sr and fission track ages is observed as depth of emplacement increases. Data on the post‐Hercynian geological evolution of Calabria were used to model in three stages the cooling and exhumation history of deep‐seated and shallow granitoids. The first stage, in Permian to Triassic times, was characterized by slow erosion. It was followed by a second stage of extensional tectonics in Jurassic times. The third stage was exhumation during the Apenninic Orogeny. The model has generated two P–T–t arrays, one for deep‐seated and the other for shallow granitoids of the Serre massif. The T–t paths suggest that the dates of micas, zircon and apatite are cooling ages. They also show that deep‐seated granitoids remained at temperatures above the brittle–plastic transition for a long time, whereas shallow granitoids cooled rapidly. Distinct P–T–t paths explain why deep‐seated and shallow granitoids display different fabric and microstructural features. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
339.
Hercynian gabbroic, dioritic and tonalitic rocks crop out in the neighbourhood of Rovale (Sila Grande, Calabria). They make up a crude rectangular outcrop with the western part consisting of gabbroic rocks and the eastern of dioritic and tonalitic rocks. They come into contact with medium to high grade metapelites on the western side and with heterogeneous granodiorites on the other sides. In the gabbroic body both opx ± ol bearing cumulates and amphibole differentiates occur and are characterized by the widespread presence of brown pargasite. Sporadic magmatic to subsolidus corona textures between olivine and plagioclase or orthopyroxene and plagioclase can be observed and their preservation clearly suggests a post-tectonic emplacement for the gabbroic magma. Diorites and tonalites display hypidiomorphic textures free of olivine and orthopyroxene and bearing green Mg-hornblende. The granitoids, on the basis of chemical data, display orogenic features of the continent-continent collision type. The gabbroic rocks have high Al tholeiitic composition and fractionation of orthopyroxene and plagioclase played an important part in their evolution. The Rb/Sr isochron method did not give a precise emplacement age for the granitoids as a whole. Initial 87Sr/86Sr ratios (at 290 Ma) are higher in the gabbroic body (0.7091–0.7095) than in diorites and tonalites (0.7083–0.7092). Thus gabbroic rocks appear more displaced than diorites and tonalites towards crustal isotopic composition. The eNd data seem to confirm this feature, thus suggesting that the gabbroic rocks and diorites derived from distinct mantle magma batches. Interestingly, small isotropic gabbroic masses occur within the diorites and show general features that allow them to be considered as possibly parental with respect to the host diorites. The evolution to the dioritic composition might have occurred through fractionation and minor mixing with a more acidic component such as the northern granodiorites. Geochemical, Sr and Nd isotopic data indicate a scenario of a composite plutonic body formed by distinct magma batches of mixed crust and mantle origin. 相似文献