A probabilistic approach for estimating the seismic response of elasto‐plastic SDOF systems

The seismic response of elasto‐plastic structures to both recorded and generated accelerograms is characterized by a large scattering of the results, even for accelerograms with similar peak ground acceleration values and frequency content. According to current code recommendations a design value of the seismic response of an elasto‐plastic structure can be computed as the mean of the responses to a certain number of spectrum‐fitting generated accelerograms. A more effective probabilistic approach is presented herein. It allows the analyst to calculate a design value of the seismic response characterized by a predefined non‐exceedance probability using a limited number of generated accelerograms. The results of the performed analyses are presented in diagrams that can be used for structural design applications. The applicability of the proposed method is demonstrated in the case of an elasto‐plastic structural system and the results are compared with those obtained applying current code recommendations. Copyright © 2005 John Wiley & Sons, Ltd.     

A boundary integral equation technique for visco-elastic stress analysis

On the basis of the correspondence principle of visco-elasticity, an application is discussed of the boundary integral equation method to the solution of time-dependent stress analysis problems. The adopted solution technique, in addition to the time-dependent stress and strain distributions, enables the determination of a measure of the error affecting the numerical results. The governing equations for the plane strain visco-elastic problem are derived with reference to a generalized Kelvin model consisting of the series of any number of simple kelvin elements, having both volumetric and deviatoric components. To get some insight into the overall performance of the technique, the results obtained in the solution of some test examples are discussed and compared with those dering from the available closed from solutions.     

Seasonal variation of particulate organic compounds in atmospheric PM10 in the biggest municipal waste landfill of Algeria

The average composition and seasonal variations of atmospheric organic particulates with respect to n-alkanes, n-alkanoic acid, polycyclic aromatic hydrocarbon (PAHs), and nitrated polycyclic aromatic hydrocarbons (N-PAHs) were determined at the biggest municipal waste landfill in Algeria located in Oued Smar, 13 km east of downtown Algiers. Samplings were carried out from August 2002 to February 2003, and organic compounds adsorbed in air particles having an aerodynamic diameter lower than 10 μm (PM₁₀) were characterized using gas chromatography coupled with mass spectrometric detection (GC/MSD). Total concentrations ranged from 828 to 11,068 ng per cubic meter of air for n-alkanes, from 1714 to 21,710 ng per cubic meter of air for n-alkanoic acids, from 13 to 212 ng per cubic meter of air for PAHs and from 93 to 205 pg per cubic meter of air for N-PAHs. n-Alkanoic acids accounted for 85 and 56% of the total organic composition of the aerosol measured in summer and winter, respectively, were the biggest fraction. The distribution profiles and the diagnostic ratios of some marker compounds allowed to identify the combustion and microbial activity as the major sources of particulate organic pollutants associated with direct emission. The year-time dependence of organic fraction content of aerosol in Oued Smar appeared to be related to average meteorological conditions as well as variability of rate and nature of materials wasted into the landfill.     

Tonian to early Cryogenian synorogenic basin of the São Gabriel Terrane,Dom Feliciano Belt,southernmost Brazil

A provenance and stratigraphic study of the Neoproterozoic Pontas do Salso Complex (PSC), western portion of the Dom Feliciano Belt (DFB), was conducted with U–Pb zircon geochronological analysis of the metasediments and the host rocks. The U–Pb isotopic data from detrital zircon of the metasediments indicate the source from the latest Middle Tonian to Late Cryogenian (between 897 and 684 Ma) and maximum depositional age of 685 ± 18 Ma in an arc-related basin setting adjacent in the Sao Gabriel Arc. The metasediments of the PSC form an elongated body in the N35°E direction and occur in the central portion of the São Gabriel Terrane (SGT), which is constituted by ophiolitic complexes and arc-related rocks, generated probably during the final consolidation of Rodinia supercontinent, although this question is still open. Low- to medium-K calc-alkaline, metaluminous affinity, and trace-element geochemistry suggest that the chemical composition of the protoliths was generated from metasomatized mantle sources in subduction zones. The PSC is composed of meta-arkoses, with subordinate metaconglomerates and metapelites. The meta-arkoses are disposed in plane-parallel layers, which also internally feature small-scale cross-bedding structures. The matrix has a blastopsammitic, poorly selected, fine to coarse texture, and hexagonal quartz and plagioclase porphyroclasts with superimposed thermal metamorphism. The polymict metaconglomerates are matrix-supported, with 15–55% of clasts of metavolcanic rocks, metasediments, undeformed granites, and quartz veins. The metapelites comprise mainly muscovite phyllites with syn-tectonic garnet and chloritoid porphyroblasts. The PSC represents a sedimentary succession deposited on an arc-related basin formed during the collapse and uplift of the SGT.     

Community structure of bathyal decapod crustaceans off South-Eastern Sardinian deep-waters (Central-Western Mediterranean)

Community structure and faunal composition of bathyal decapod crustaceans off South-Eastern Sardinian deep-waters (Central-Western Mediterranean) were investigated. Samples were collected during 32 hauls between 793 and 1598 m in depth over the 2003–2007 period. A total of 1900 decapod specimens belonging to 23 species were collected. Multivariate analysis revealed the occurrence of three faunistic assemblages related to depth: (i) an upper slope community at depths of 793–1002 m; (ii) a middle slope community at depths of 1007–1212 m and (iii) a lower slope community at depths greater 1420 m. In the upper and middle slopes the benthic ( Polycheles typhlops ) and epibenthic–endobenthic feeders (mainly Aristeus antennatus and Geryon longipes ), which eat infaunal prey, were dominant, followed by the macroplankton–epibenthic feeders such as Acanthephyra eximia and Plesionika acanthonotus . In the deepest stratum, the most remarkable feature was the prevalence of macroplankton–epibenthic feeders ( A. eximia and P. acanthonotus ). A small percentage of the benthic deep-sea lobster Polycheles sculptus was also present. The biomass presented higher values in the middle slope and declined strongly in the lower slope. There was no general pattern of mean individual weight/size versus depth among decapods, and the changes seemed to be species-specific with different trends.     

Magnetometer survey of the proposed Sirente meteorite crater field,central Italy: Evidence for uplifted crater rims and buried meteorites

Abstract— The Sirente crater field consists of a 120 m wide, rimmed main depression flanked to the northwest by about 30 smaller depressions. It has been dated to the first centuries A.D. An impact origin is suggested, but not confirmed. The small size combined with the properties of the target material (carbonate mud) would neither allow shock features diagnostic of impact, nor projectile vaporization. Consequently, a meteoritic component in the sediments would be very localized. At impacts of this size the projectile most likely is an iron meteorite. Any iron meteorites on the ground surface would, in Iron Age Europe, have been removed shortly after the event. However, if the depressions are of impact origin they should contain meteorites at great depth in analogy with known craters. The magnetic properties of iron meteorites differ distinctly from the very low magnetic sediments and sedimentary rocks of the Sirente area. We have used a proton precession magnetometer/gradiometer to produce magnetic anomaly maps over four of the smaller depressions (～8 m diameter), as well as two crossing profiles over a fifth depression (～22 m diameter). All show distinct magnetic anomalies of about 20 nT, the larger depression up to 100 nT. Magnetic modeling shows a best fit for structures with upturned strata below their rims, excluding a karstic origin but supporting an explosive formation. The 100 nT anomaly can only be explained by highly‐magnetic objects at a few meters depth. All together, the magnetic data provides a strong indication for an impact origin of the crater field.     

Heavy metal contamination in surface sediments from the Gulf of Venice, Italy

The authors studied surface sediments from 102 stations in four areas of the three port entrances to the Lagoon of Venice, examining the relationships between textural character, mineralogical composition, and Hg, Pb, Cd, Cu, Ni, Cr, Zn, Co and Fe content. Heavy metal distribution allowed boundaries to be fixed between polluted and nonpolluted zones. While the Cavallino area is not polluted, very high concentrations of Zn, Pb and Hg in the two central areas, facing the Lido and Malamocco port entrances, respectively, suggest that wastes mainly from industrial production of zinc are present. High concentrations of Cr in the southern part of the Chioggia area are probably due to tannery wastes reaching the sea from the Brenta river.     

Volcanological and magmatological evolution of Stromboli volcano (Aeolian Islands): The roles of fractional crystallization,magma mixing,crustal contamination and source heterogeneity

The present paper reports the results of a detailed stratigraphical, petrological and geochemical investigation on the island of Stromboli, Aeolian arc, Southern Tyrrhenian sea. Major and trace element data determined on a large quantity of samples from well-established stratigraphic positions indicate that the magmatological evolution of the island through time was more complex than previously known. The activity of the exposed part of Stromboli, which occurred over a time span of about 100 000 years, started with the emission of high-K calc-alkaline (HKCA) volcanics, which were covered by calc-alkaline (CA), shoshonitic (SHO), high-K calc-alkaline (HKCA) and potassic (KS) products. The most recent activity consists of HKCA lavas and the present-day SHO-basaltic volcanics emitted by mildly explosive “strombolian” activity. Most of the products are lavas, with minor amounts of pyroclastic rocks emplaced mainly during the early stages of activity. The transition from the SHO to the KS cycle was associated with the collapse of the upper part of the volcanic apparatus; the transition from KS to the present-day SHO activity has been found to have occurred at the time of the sliding of the western portion of the volcano that generated the “Sciara del Fuoco” depression. The rock series cropping out at Stromboli show variable enrichment in potassium, incompatible trace elements and radiogenic Sr which increase from CA through HKCA, and SHO up to KS rocks. Major, trace element and Sr-isotopic data agree in indicating that the HKCA and SHO series evolved by crystal/liquid fractionation starting from different parental liquids, whereas crustal assimilation appears to have been the leading process during the evolution of KS volcanics. Mixing processes also played a role although they can be well documented only when they occurred between magmas with different isotopic and geochemical characteristics. Geochemical modelling based on trace element and isotopic data indicates that the mafic magmas of the different volcanic series may be generated by melting of an upper mantle heterogeneously enriched in incompatible elements and radiogenic Sr by addition, via subduction, of different amounts of crustal material. Geochemical data, however, are also in agreement with the alternative hypothesis that the most mafic magmas of the different series have been generated by combined processes of fractional crystallization, assimilation and mixing of a CA magma in a deep-sited magma chamber; the mafic magmas formed by these complex processes were successively emplaced in a shallow reservoir where they evolved by simple fractional crystallization (HKCA and SHO series) and by assimilation of crustal material (KS). The occurrence of changes in the geochemical signatures of the magmas at the time of the structural modification of the volcano is believed to favour the hypothesis that the variable composition observed in the volcanic rocks of Stromboli is the result of processes occurring within the volcanic system.     

Petrology and geochemistry of potassic and ultrapotassic volcanism in central Italy: petrogenesis and inferences on the evolution of the mantle sources

Major, trace element, Sr isotopic and mineral chemical data are reported for mafic volcanic rocks (Mg-value 65) from the northern-central sector of the potassic volcanic belt of Central Italy. The rocks investigated range from potassic series (KS) and high-K series (HKS) to lamproitic (LMP) and kamafugitic (KAM) through a transitional series (TRANS), thus covering the entire compositional spectrum of potassic and ultrapotassic magmas. KAM rocks are strongly silica undersaturated and, compared with the other rock series, have low SiO₂, Al₂O₃, Na₂O, Sc and V and high CaO, K/Na, (Na + K)/Al. KS and HKS have high Al₂O₃, CaO and variable enrichment in K₂O and incompatible elements. LMP rocks are saturated in silica and have high SiO₂, K₂O, K₂O/Na₂, MgO, Ni and Cr and low Al₂O₃, CaO, Na₂O, Sc and V. TRANS rocks display intermediate compositional characteristics between LMP and KS.

All the rocks under study have fractionated hygromagmaphile element patterns with high LIL/HFS element values and negative anomalies of Ti, Ta, Nb and Ba. Negative Sr anomalies are observed in the LMP and TRANS rocks. LIL elements show overall positive correlations with K₂O, whereas different trends of Sr and HFSE vs. K₂O are defined by LMP-TRANS and KS-HKS-KAM. ⁸⁷Sr/⁸⁶Sr range from about 0.710 to 0.716. KS, HKS and KAM rocks have similar ⁸⁷Sr/⁸⁶Sr values clustering around 0.710. LMP and TRANS rocks have the highest ⁸⁷Sr/⁸⁶Sr values.

Geochemical and isotopic data reported for the most primitive Italian potassic and ultrapotassic rocks support the hypothesis that the interaction between crustal and mantle reservoirs was a main process in the genesis of Italian potassic magmatism. Simple mass balance calculations exclude, however, an important role of crustal assimilation during ascent of subcrustal magmas to the surface and indicate that the sources of Central Italy volcanics underwent contamination with fluids and/or melts released by upper crustal material previously brought into the mantle by subduction processes.

Different trends of incompatible elements vs. K₂O observed in the studied rocks suggest distinct metasomatic processes for the sources of the investigated magmas. Liquids derived by bulk melting of pelitic sediments are believed to be the most likely contaminants of the source of LMP rocks. Fluids or melts rich in Ca, Sr and with high LILE/HFSE value and Sr isotopic composition around 0.710 are the most likely contaminant of the source region of KS, HKS and KAM volcanics. Variations in CaO, Na₂O and ferromagnesian element abundances and ratios suggest that, in some zones, the mantle source of potassic magmas experienced partial melting with extraction of basaltic liquids prior to metasomatism.