Geophysical investigation of the Sandalp rock avalanche deposits

In the study of rock avalanche phenomena, numerical modelling makes use of back analyses of the rock avalanche propagation for calibration of the modelling assumptions and parameters. The back analyses require knowledge of the run-out area boundaries and the thickness distribution of the deposit. Geophysical methods can be applied to retrieve the thickness distribution, but, due to strong heterogeneities and logistic problems they are seldom applied. The aim of this work is to assess the potential of integrated geophysical methods to recognise and characterise a deposit created by two rock avalanches which occurred in the Sandalp valley (Switzerland) in 1996. The topography of the site before and after the rock avalanche is known and can be used as a benchmark. Resistivity tomography, seismic P-wave tomography, and active and passive surface wave analysis have been applied on several profiles deployed both on the rock avalanche deposit and in the surrounding area. Innovative approaches for surface wave analysis based on laterally constrained inversion and multimodal inversion have been applied to the data. A comparison of the results of the geophysical investigations with the topographic benchmark has shown the capability of the geophysical methods to locate the bottom of the deposit in the areas where the contrast with the host sediments properties is significant. In these areas, the deposit has higher resistivities and lower seismic velocities than the underlying materials. In the areas where the deposit is thicker and richer in fine-grained materials the geophysical parameters are not able to discriminate between the rock avalanche deposit and the underlying sediments. As a secondary task, the geophysical methods also allowed the bedrock pattern to be outlined.     

Lissajous trajectories for lunar global positioning and communication systems

This work proposes a Lunar Global Positioning System (LGPS) and a Lunar Global Communication System (LGCS) using two constellations of satellites on Lissajous trajectories around the collinear L ₁ and L ₂ libration points in the Earth–Moon system. This solution is compared against a Walker constellation around the Moon similar to the one used for the Global Positioning System (GPS) on the Earth to evaluate the main differences between the two cases and the advantages of adopting the Lissajous constellations. The problem is first studied using the Circular Restricted Three Body Problem to find out its main features. The study is then repeated with higher fidelity using a four-body model and higher-order reference trajectories to simulate the Earth-Moon-spacecraft dynamics more accurately. The LGPS performance is evaluated for both on-ground and in-flight users, and a visibility study for the LGCS is used to check that communication between opposite sides of the Moon is possible. The total ΔV required for the transfer trajectories from the Earth to the constellations and the trajectory control is calculated. Finally, the estimated propellant consumption and the total number of satellites for the Walker constellation and the Lissajous constellations is used as a performance index to compare the two proposed solutions.     

Sediment chemical contamination of a shallow water area close to the industrial zone of Porto Marghera (Venice Lagoon, Italy)

The industrial zone of Porto Marghera is one the most important "contaminated sites of national interest" (SIN) in Italy, being identified as an area of high environmental risk. The site includes a wide shallow water area of the Venice Lagoon extending toward the city of Venice, which was investigated in order to acquire information on the pollutant level and distribution. Grain-size, heavy metal, nutrient, and organic micropollutant concentrations were determined in the surface sediment layers (0-5 and 5-10 cm depths) of 51 sites. A generally low contamination was found, except for Hg concentration, which increases the toxicological risk in most of the sites of the area, according to the results of a comparison with Sediment Quality Guidelines. A heavy pollution fingerprint (Cd, Cu, Hg, Pb, and Zn up to 15.2, 257, 11.9, 248, and 3010 mg/kg d.w., respectively) was instead found near the Tresse Island, which is ascribed to the spill of pollutants from the contaminated sediment disposed therein. Grain-size and heavy metal profiles down to a depth of 40 cm in eight selected sites, finally show a probable decrease of the pollution affecting the area in recent years.     

Influence of glass polymerisation and oxidation on micro-Raman water analysis in alumino-silicate glasses

The development of an accurate analytical procedure for determination of dissolved water in complex alumino-silicate glasses via micro-Raman analysis requires the assessment of the spectra topology dependence on glass composition. We report here a detailed study of the respective influence of bulk composition, iron oxidation state and total water content on the absolute and relative intensities of the main Raman bands related to glass network vibrations (LF: ∼490 cm⁻¹; HF: ∼960 cm⁻¹) and total water stretching (H₂O_T: ∼3550 cm⁻¹) in natural glasses. The evolution of spectra topology was examined in (i) 33 anhydrous glasses produced by the re-melting of natural rock samples, which span a very large range of polymerisation degree (NBO/T from 0.00 to 1.16), (ii) 2 sets of synthetic anhydrous basaltic glasses with variable iron oxidation state (Fe³⁺/Fe_T from 0.05 to 0.87), and (iii) 6 sets of natural hydrous glasses (C_H2OT from 0.4 to 7.0 wt%) with NBO/T varying from 0.01 to 0.76.In the explored domain of water concentration, external calibration procedure based on the H₂O_T band height is matrix-independent but its accuracy relies on precise control of the focusing depth and beam energy on the sample. Matrix-dependence strongly affects the internal calibrations based on H₂O_T height scaled to that of LF or HF bands but its effect decreases from acid (low NBO/T, SM) to basic (high NBO/T, SM) glasses. Structural parameters such as NBO/T (non-bridging oxygen per tetrahedron) and SM (sum of structural modifiers) describe the matrix-dependence better than simple compositional parameters (e.g. SiO₂, Na₂O + K₂O). Iron oxidation state has only a minor influence on band topology in basalts and is thus not expected to significantly affect the Raman determinations of water in mafic (e.g. low SiO₂, iron-rich) glasses. Modelling the evolution of the relative band height with polymerisation degree allows us to propose a general equation to predict the dissolved water content in natural glasses:

     

Retention of biosignatures and mass-independent fractionations in pyrite: Self-diffusion of sulfur

Self-diffusion of sulfur in pyrite (FeS₂) was characterized over the temperature range ∼500-725 °C (∼1 bar pressure) by immersing natural specimens in a bath of molten elemental ³⁴S and characterizing the resulting diffusive-exchange profiles by Rutherford backscattering spectroscopy (RBS). The temperature dependence of the sulfur diffusivity (D_S) conforms to D_S = D_o exp(−E_a/RT), where the pre-exponential constant (D_o) and the activation energy (E_a) are constrained as follows:

     

Are fossil groups a challenge of the cold dark matter paradigm?

We study six groups and clusters of galaxies suggested in the literature to be 'fossil' systems (i.e. to have luminous diffuse X-ray emission and a magnitude gap of at least 2 mag R between the first and the second ranked member within half of the virial radius), each having good quality X-ray data and Sloan Digital Sky Survey (SDSS) spectroscopic or photometric coverage out to the virial radius. The poor cluster AWM 4 is clearly established as a fossil system, and we confirm the fossil nature of four other systems (RX J1331.5+1108, RX J1340.6+4018, RX J1256.0+2556 and RX J1416.4+2315), while the cluster RX J1552.2+2013 is disqualified as fossil system. For all systems, we present the luminosity functions within 0.5 and 1 virial radius that are consistent, within the uncertainties, with the universal luminosity function of clusters. For the five bona fide fossil systems, having a mass range  2 × 10¹³–3 × 10¹⁴ M_⊙  , we compute accurate cumulative substructure distribution functions (CSDFs) and compare them with the CSDFs of observed and simulated groups/clusters available in the literature. We demonstrate that the CSDFs of fossil systems are consistent with those of normal observed clusters and do not lack any substructure with respect to simulated galaxy systems in the cosmological Λ cold dark matter (ΛCDM) framework. In particular, this holds for the archetype fossil group RX J1340.6+4018 as well, contrary to earlier claims.     

Elastic model for the gravity and elevation changes before the 2001 eruption of Etna volcano

For 5 months before the 2001 Mt. Etna eruption, a progressive gravity decrease was measured along a profile of stations on the southern slope of the volcano. Between January and July 2001, the amplitude of the change reached 80 μGal, while the wavelength of the anomaly was of the order of 15 km. Elevation changes observed through GPS measurements during a period encompassing the 5-month gravity decrease, remained within 4–6 cm over the entire volcano and within 2–4 cm in the zone covered by the microgravity profile. We review both gravity and elevation changes by a model assuming the formation of new cracks, uniformly distributed in a rectangular prism. The inversion problem was formulated following a global optimization approach based on the use of Genetic Algorithms. Although it is possible to explain the observed gravity changes by means of the proposed analytical formulation, the results show that calculated elevation changes are significantly higher than those observed. Two alternative hypotheses are proposed to account for this apparent discrepancy: (1) that the assumptions behind the analytical formulation, used to invert the data, are fallacious at Etna, and thus, numerical models should be utilized; (2) that a second process, enabling a considerable mass decrease to occur without deformation, acted together with the formation of new cracks in the source volume.     

Ground-Motion Scaling in the Western Alps

In order to empirically obtain the scaling relationships for the high-frequency ground motion in the Western Alps (NW Italy), regressions are carried out on more than 7500 seismograms from 957 regional earthquakes. The waveforms were selected from the database of 6 three-component stations of the RSNI (Regional Seismic network of Northwestern Italy). The events, M _W ranging between 1.2 and 4.8, were recorded within a hypocentral distance of 200 km during the time period: 1996–2001. The peak ground velocities are measured in selected narrow-frequency bands, between 0.5 and 14 Hz. Results are presented in terms of a regional attenuation function for the vertical ground motion, a set of vertical excitation terms at the reference station STV2 (hard-rock), and a set of site terms (vertical and horizontal), all relative to the vertical component of station STV2.The regional propagation of the ground motion is modeled after quantifying the expected duration of the seismic motion as a function of frequency and hypocentral distance. A simple functional form is used to take into account both the geometrical and the anelastic attenuation: a multi-variable grid search yielded a quality factor Q(f) = 310f ^0.20, together with a quadri-linear geometrical spreading at low frequency. A simpler, bi-linear geometrical spreading seems to be more appropriate at higher frequencies (f > 1.0 Hz). Excitation terms are matched by using a Brune spectral model with variable, magnitude-dependent stress drop: at M _w 4.8, we used Δσ = 50 MPa. A regional distance-independent attenuation parameter is obtained (κ₀ = 0.012 s) by modelling the average spectral decay at high frequency of small earthquakes.In order to predict the absolute levels of ground shaking in the region, the excitation/attenuation model is used through the Random Vibration Theory (RVT) with a stochastic point-source model. The expected peak-ground accelerations (PGA) are compared with the ones derived by Ambraseys et al. (1996) for the Mediterranean region and by Sabetta and Pugliese (1996) for the Italian territory.