Seismic characterization of shallow bedrock sites with multimodal Monte Carlo inversion of surface wave data

Sites with a limited overburden over a stiff basement are of particular relevance for seismic site response. The characterization of such stratigraphies by means of surface wave methods poses some difficulties in interpretation. Indeed the presence of sharp seismic contrasts between the sediments and the shallow bedrock is likely to cause a relevance of higher modes in the surface wave apparent dispersion curve, which must be properly taken into account in order to provide reliable results. In this study a Monte Carlo algorithm based on a multimodal misfit function has been used for the inversion of experimental dispersion curves. Case histories related to the characterization of stations of the Italian accelerometric network are reported. Spectral ratios and amplification functions associated to each site are moreover evaluated to provide an independent benchmark test. The results show the robustness of the inversion method in such non-trivial conditions and the possibility of getting an estimate of uncertainty related to solution non-uniqueness.     

Comet Machholz (C/2004 Q2): morphological structures in the inner coma and rotation parameters

Extensive observations of comet C/2004 Q2 (Machholz) were carried out between August 2004 and May 2005. The images obtained were used to investigate the comet’s inner coma features at resolutions between 350 and 1500 km/pixel.     

Production of metaluminous melt during fluid‐present anatexis: an example from the Maghrebian basement,La Galite Archipelago,central Mediterranean

Garnet brought to the surface by late Miocene granitoids at La Galite Archipelago (Central Mediterranean, Tunisia) contains abundant primary melt and fluid inclusions. Microstructural observations and mineral chemistry define the host garnet as a peritectic phase produced by biotite incongruent melting at ~800 °C and 0.5 GPa, under fluid‐present conditions. The trapped melt is leucogranitic with an unexpected metaluminous and almost peralkaline character. Fluid inclusions are one phase at room temperature, and contain a CO₂‐dominated fluid, with minor H₂O, N₂ and CH₄. Siderite and an OH‐bearing phase were identified by Raman and IR spectroscopy within every analysed inclusion, and are interpreted as products of a post‐entrapment carbonation/hydration reaction between the fluid and the host during cooling. The fluid present during anatexis is therefore inferred to have been originally richer in both H₂O and CO₂. The production of anatectic melt with a metaluminous signature can be explained as the result of partial melting of relatively Al‐poor protoliths assisted by CO₂‐rich fluids.     

Anatomy of a late Pleistocene clinoformal sedimentary body (Le Castella,Calabria, southern Italy): A case of prograding spit system?

The Le Castella marine terrace is the smallest and youngest terrace of the Crotone area (southern Italy), and formed after a rapid marine ingression due to a glacio-eustatic rise outpacing the regional uplift of the area. The most prominent feature of the terrace deposits is a seaward-accreting clinoform about 10 m thick, inferred to be formed during forced regressive conditions. This prograding body is mostly composed of bioclastic material, and shows an internal complexity consisting of alternating oblique and sigmoid elementary units inferred to be produced mainly by changes of accommodation development. Foreset avalancing was due to sediment accumulation by gravity-flow processes, while topsets were characterized by the migration of medium- to large-scale dunes showing a unimodal palaeocurrent pattern, oblique with respect to the dip direction of the large-scale clinoform foresets. The Le Castella clinoform starts to develop from a topographic step on the basement due to tectonics, which also controlled the palaeoshoreline trend.The recognized stratigraphic and facies architectures, the palaeocurrent pattern, and the inferred palaeogeographic setting during deposition, all suggest that the Le Castella clinoform is an example of spit system attached to the mainland and accreted due to longshore transport. The present example contributes to establish criteria allowing the recognition of ancient spit systems, which still are poorly known and rarely documented in the pre-Quaternary geological record.     

GNSS software receiver for the MAGIA (Missione Altimetrica Geofisica GeochImica lunAre) mission

In recent years a number of missions have been conceived to acquire and track signals from GPS satellites at altitudes higher than the GPS constellation itself. The main purpose of SDR is to reduce the number of hardware components, projected for specific unmodifiable uses, and utilize general purpose units: on board CPU, DSP or FPGA. In this paper he study and design of a GNSS Software Receiver for space application, applied to a Lunar Mission, is presented with particular attention on Space Segment device and on Ground Facilities.     

Magnetostratigraphic dating of an intensification of glacial activity in the southern Italian Alps during Marine Isotope Stage 22

We applied magnetostratigraphy and mammal biostratigraphy to date climate-sensitive pollen cycles and lithostratigraphic units of the Pliocene-Pleistocene Leffe sedimentary succession from the Southern Alps, Italy. The Leffe section was correlated to additional sections (Casnigo, Fornaci di Ranica, and Pianengo) to construct a stratigraphic network along a common fluviatile system (the Serio River) sourced in the Southern Alps and flowing southward into the Po River Basin. We obtained a coherent scenario of climate variability for the last ∼ 2 Myr. At Leffe, lacustrine deposition commenced during the Olduvai Normal Subchron (1.94-1.78 Ma) and lasted up to a chronologic level compatible with Marine Isotope Stage (MIS) 22 (0.87 Ma). Pollen analysis revealed that climate varied cyclically from warm-temperate to cool during this time interval, but never as cold as during glacial intervals. At around MIS 22, climate cooled globally. Gravels, attributed to high-energy braided river systems fed locally by alluvial fans, prograded from the Serio River catchment area over the Leffe Basin and toward the Po Plain in response to a generalized event of vegetation withdrawal and enhanced physical erosion. At this time, Alpine valley glaciers reached their first maximum southward expansion with glacier fronts located at only ∼ 5 km upstream from Leffe.