Compositional variation in the 1983 and other recent Etnean lavas: Insights on the shallow feeding system

A systematic petrographic and chemical study of chronologically ordered lava samples collected during the 1983 Etna eruption, has shown minor fluctuating variations in crystallinity and chemistry, apparently correlated with variations in the rate of effusion. Comparison with the compositional variations observed in the lavas emitted during the 1971–1983 period, has revealed a repeated evolutional tendency suggesting a small size shallow storage system periodically refilled, as in 1983, by more primitive magma.     

Stabilized finite elements for harmonic soil dynamics problems near the undrained-incompressible limit

Simple Finite Element models for soil dynamics and earthquake engineering problems in the frequency domain are a fast and valuable tool providing a first approximation before a full non-linear analysis in the time domain is performed.Quite often the problem concerns saturated soils with very small permeability and pore fluid of neglectable compressibility. In the limit, the permeability is assumed to be zero and the pore fluid incompressible. Here, engineers use standard finite element codes formulated in terms of displacements but incompressibility may result in volumetric locking of the mesh with a severe loss of accuracy.The purpose of this paper is to present a simple mixed finite element formulation in the frequency domain based on displacements and pore pressures as main variables. A suitable stabilization technique allowing for equal order interpolation of displacements and pressures has been introduced for incompressible and zero permeability limits.Of course, the range of application is limited to those problems in which the behaviour of the material can be approximated by linear models, and therefore modelling of phenomena such as liquefaction, cyclic mobility or cavitation occur is excluded.The paper shows as well an extremely simple way of coupling solid and water domains as it occurs for instance in quay walls under dynamic loading.     

Traffic-related platinum group elements (PGE) in soils from Mexico City

The first evaluation of the distribution of platinum group elements (PGE) derived from automobile catalytic converters in urban soil samples in Mexico City was carried out. There are more than four millions cars in Mexico City and, at the present time, one third of them have catalytic converters. PGE concentrations in soils exposed to high traffic densities exceed the natural background values by upto two orders of magnitude and are directly influenced by traffic conditions. The highest concentrations of Pt, Pd and Rh in the analyzed samples are about 300, 70 and 40 μg/l, respectively. Although the PGE concentrations found in soil samples are relatively low, they represent an accumulation of only 10 yr. It is likely that the use of catalytic converters will dramatically change the distribution of these metals in the urban environment in the next decades.     

Triple-junction migration during Paleozoic plate convergence: the Aracena metamorphic belt, Hercynian massif, Spain

New data on the petrology and structure of the Aracena metamorphic belt shows that this is a subduction-related, low-pressure/high-temperature complex developed by plate convergence at the north margin of Gondwana during the Paleozoic. The low-pressure, inverted metamorphic gradient in MORB-derived amphibolites resulted from heating from the continental hanging wall during subduction. This implies that the previous heating of the continental rocks was related to subduction of an oceanic ridge and the creation of a slab window beneath the continental margin. This slab window brought the asthenosphere in contact with the continental margin inducing a shallow thermal anomaly and partial melting of the lithospheric mantle resulting in boninite magmatism.     

On the instability region around the 5 : 3 Jovian resonance

Variations in the dynamic parameters of Phobos have been determined after reaching critical value of the semi-major axis = 7247 km at which zero-gravity on the surface of Phobos near the equator will take place. The rate of the variations will increase significantly, e.g., in the tidal energy dissipation by one order in magnitude. The total dissipated mechanical energy during the whole tidal history of the system has been estimated as -5.5 × 10²¹ kg m² s^-2, the total decrease in the second zonal Stokes parameter of Phobos as -6.6 × 10^-2.     

Mercury levels in the dissolved and particulate fractions of the Tyrrhenian sea

Determination of the actual mercury concentration in Mediterranean basin seawater was achieved by means of an instrument based on fluorescence spectrometry developed for this purpose, during a field study aboard the oceanographic ship “L.F. Marsili”, between August 1980 and May 1982.Dissolved ·total’ and ·reactive’ mercury and mercury associated with particulate matter were determined on surface and subsurface waters in the Tyrrhenian Sea from La Spezia to Sicily.Concentrations in the range 1.4–19.7 ng l⁻¹ for ·total dissolved mercury’, 0.5–5.9 ng l⁻¹ for ·reactive dissolved mercury’ and 0.3–8.0 ng l⁻¹ for mercury associated with the particulate matter, were measured on surface and subsurface waters in the Tyrrhenian Sea from La Spezia to Sicily.Even if the mean value of the total mercury concentration (dissolved + particulate) was found to be about twice as high as those observed for the oceans, the difference does not seem to be as high as predicted by the model proposed by Buffoni and co-workers to explain the large difference of mercury levels between tunas caught, respectively, in the Mediterranean and in the Oceans.     

Comparison of the fish assemblages associated with Posidonia oceanica after the partial loss and consequent fragmentation of the meadow

An extensive Posidonia oceanica meadow was partially destroyed by excavation, resulting in areas of seagrass habitat of equal complexity (shoot density) but different heterogeneity (degree of fragmentation). The fish assemblages associated with differently fragmented beds were compared from a landscape perspective. Differences in the fish assemblages were detected, with several species showing different patterns: (1) species that increased their abundance along with the degree of bed fragmentation, (2) species that were more abundant in fragmented beds, but did not show differences between more or less fragmented beds, and (3) species that were mostly abundant in large seagrass patches or in the continuous meadow. The fish assemblages were also affected by depth, but further research is needed to determine properly this effect. Some ecological mechanisms are suggested to operate in the interaction between P. oceanica and the held fish assemblage.     

On NAO’s predictability through the DFA method

Summary In this paper, the authors address a predictability study of the NAO index by using the time series analysis method known as “detrended fluctuation analysis” (DFA). This technique provides a quantitative measure of predictability by computing several piecewise fits (either linear or higher degree polynomial ones) to the cumulative series of fluctuations associated to the original series. The measurements, made on several examples of data available in the Internet, agree with other previous analyses (Fernández et al, 2003) assessing that the NAO signal is a slightly red one, whose prediction needs a deeper understanding of the underlying physics.     

Seismic wave properties in time-dependent porosity homogeneous media

It is quantified the properties of seismic waves in fully saturated homogeneous porous media within the framework of Sahay's modified and reformulated poroelastic theory. The computational results comprise amplitude attenuation, velocity dispersion and seismic waveforms. They show that the behaviour of all four waves modelled as a function of offset, frequency, porosity, fluid viscosity and source bandwidth depicts realistic dissipation within the sonic–ultrasonic band. Therefore, it appears that there is no need to include material heterogeneity to model attenuation. By inference it is concluded that the fluid viscosity effects may be enhanced by dynamic porosity.