Chemical parameters characterizing the sedimentary environment in a NW Adriatic coastal area (Italy)

Organic matter constituents (C, N, P) have been measured in surficial sediment samples from a coastal area often subjected to eutrophication phenomena. Chemical and physico-chemical parameters are substantially homogeneous throughout the area investigated, indicating a mainly autochthonous origin of the sedimented organic matter and allowing some considerations on the diagenetic processes possibly occurring at the sediment-water interface in relation to nutrient release.     

Multivariate stochastic wave generation

In this paper, for the case of the fluid particle velocity, a procedure that substantially reduces the computational effort to generate a multivariate stochastic process is proposed. It is shown that, for a fully coherent wave field, it is possible to decompose the Power Spectral Density (PSD) matrix into the eigenvectors of the matrix itself. This leads to generate each field's process as independent, and the time generation increases linearly with the processes' number in the field.

A numerical example to evaluate the statistical properties, in terms of correlation and cross-correlation functions, of the processes is also presented.     

Magnetic stratigraphy of Vesuvius products. I. 1631 lavas

An extensive palaeomagnetic study has been undertaken to provide further elements leading to a better assessment of the volcanic history of the Vesuvius. This work refers to lavas for which the date of emplacement have recently been questioned; i.e. either during the period 968–1037 or in 1631. From 7 sites, 97 sun-orientated specimens have been collected. The dominant magnetic carrier for all sites consists of magnetite on the basis of an analysis of IRM acquisition. The linearity analysis carried out on at least 6 specimens per site subjected to PAFD has indicated the presence of single- and multi-component magnetizations. The within-site mean directions of 5 sites are close to each other suggesting that lavas from these sites can be ascribed to the same volcanic event. The remaining 2 sites can also be referred to this event on ground of stratigraphical considerations. The plotting of the between-site mean directions of the previously mentioned 5 sites on the Vesuvius secular variation curve suggests that the lavas from these sites could not be emplaced during the period 968–1037 but some hundred years later than 1301. The stratigraphic and historic dating of deposits and a building, respectively, at one of the 2 remaining sites allows to conclude that all the investigated flows had to be emplaced during the 1631 event. Therefore, this event was characterized not only by explosive activity but by an important effusive phase as well.     

Numerical Simulations of the Interaction of Jets with the Intracluster Medium

We study, by numerical simulations, the propagation of an axisymmetric supersonic jet in an isothermal King atmosphere and we analyse the evolution of the resulting X-ray properties and their dependence on the jet physical parameters. We show the existence of two distinct regimes of interaction, with strong and weak shocks. In the first case shells of enhanced X-ray emission are to be expected, whereas in the second case we expect deficit of X-ray emission coincident with the cocoon. Analysing the results of our simulations we find that the jet kinetic power is the main parameter controlling the transition between the two regimes. We also discuss, in the same scheme, the ICM heating induced by the jet propagation, considering its effects on the observed relations between the cluster X-ray luminosity and temperature and between cluster entropy and temperature.     

Linking the Recurrence Time of Earthquakes to Source Parameters: A Dream or a Real Possibility?

By using a single-degree-of-freedom spring-slider analog fault model, we generate a synthetic catalog of nearly 500 different seismic sequences. We explore the parameter space by assuming different values of constitutive parameters and tectonic environment. We also consider three different versions of the rate-dependent and state-dependent friction laws [the Dieterich-Ruina (DR), the Ruina-Dieterich (RD) and the Chester-Higgs (CH) models], and different approximations of the behavior of the friction at high sliding speeds, as well as the radiation damping effects. Our results indicate that for all the considered models, the recurrence time (T _cycle) exhibits an inverse proportionality on the loading rate; a linear, positive dependence on the effective normal stress; and a linear, negative dependence on the characteristic distance controlling the state variable evolution. These results confirm and generalize previous studies. Remarkably, we found here that the coefficients of proportionality strongly depend on the adopted friction model, on the high speed behavior and on the reference set of parameters. Notably, we also found that the positive proportionality between T _cycle and the difference b – a, confirmed for DR and RD laws, does not hold in general for the CH law. Overall, we conclude that even in the simplest (and idealized) case of characteristic earthquakes considered here, in which the limiting cycle is reached by the system, and even in the framework of a very simplified fault model, the possibility to a priori predict, through an universal analytical relation, the inter-event time of an impending earthquake still remains only a dream. On the other hand, a numerical prediction of T _cycle would require the exact knowledge of the rheological model (and its parameters at all times over the entire life of the fault) and the actual state of the fault, which indeed are often unknown.     

Earthquakes from 1820 to 1936 in Grahamstown and surroundings (Eastern Cape Province,South Africa)

The seismicity of Grahamstown, in the Eastern Cape Province of South Africa, for the years between 1820 and 1936 is investigated with recourse to contemporaneous documentary sources, leading to the development of a seismic history incorporating consideration of the broader geo-political context. Individual studies of five regional events that were felt in Grahamstown during that period, and of one that was not, are presented. Each study includes the development of a full set of intensity data points, which are used to determine reappraised epicentral locations and magnitudes, some of which differ significantly from previously listed parameters. The results thus obtained highlight the value of seeking out additional contemporary sources from different language groups when revisiting the source parameters of earthquakes for which no or only very limited instrumental information is available.     

Interaction between deep and shallow groundwater systems in areas affected by Quaternary tectonics (Central Italy): a geochemical and isotope approach

Hydro- and isotope geochemistry are used to refine groundwater conceptual models in two areas of central Italy (Acque Albule Basin and Velino River Valley) affected by extensional Quaternary tectonics, where deep and shallow groundwater flow systems are interacting. The role of geology, of recent deposits filling the plains and of main tectonic features controlling groundwater flowpaths and deep-seated fluids emergences are investigated and discussed. Environmental isotopes (²H and ¹⁸O) confirm recharge in the surrounding carbonate aquifers, and meteoric origin of both shallow and deep groundwater. Major ion chemistry indicates a mixing between shallow Ca-HCO₃ groundwater from carbonate aquifers and deep Ca-HCO₃-SO₄ groundwater, characterised by higher salinity and temperature and high concentration in sulphates. Isotopic composition of dissolved sulphates (δ ³⁴S and δ ¹⁸O) and dissolved inorganic carbon (δ ¹³C), henceforth indicated as DIC, are used to verify the presence of different sources of groundwater, and to validate the mixing model suggested by the major ion analyses. Sulphate isotope composition suggests a marine origin for the groundwater characterised by elevated sulphate concentration, whose source is present in the deep buried sequences. Carbon isotope composition confirms the role of a DIC source associated to CO₂ degassing of a deep reservoir. Groundwater conceptual models are improved underlining the importance of Plio-Pleistocene sequences filling the tectonic depression. In the Acque Albule area, the travertine plateau represents a mixing stratified aquifer, where deep groundwater contribution is spread into the shallow aquifer. The alluvial–clastic–lacustrine leaky aquifer of Velino Valley enables a complete mixing of shallow and deep groundwater allowing spot-located discharge of deep groundwater along tectonic patterns and facilitating sulphate reduction in the lacustrine sediments, explaining locally the presence of H₂S.