Time-space variation of volcano-seismic events at La Fossa (Vulcano, Aeolian Islands, Italy): new insights into seismic sources in a hydrothermal system

We investigated the relationship between volcano-seismic events, recorded at La Fossa crater of Vulcano (Aeolian Islands, Italy) during 2004-2006, and the dynamics of the hydrothermal system. During the period of study, three episodes of increasing numbers of volcano-seismic events took place at the same time as geothermal and geochemical anomalies were observed. These geothermal and geochemical anomalies have been interpreted as resulting from an increasing deep magmatic component of the hydrothermal fluids. Three classes of seismic events (long period, high frequency and monochromatic events), characterised by different spectral content and various similarity of the waveforms, have been recognised. These events, clustered mainly below La Fossa crater area at depths of 0.5–1.1 km b.s.l., were space-distributed according to the classes. Based on their features, we can infer that such events at Vulcano are related to two different source mechanisms: (1) fracturing processes of rocks and (2) resonance of cracks (or conduits) filled with hydrothermal fluid. In the light of these source mechanisms, the increase in the number of events, at the same time as geochemical and geothermal anomalies were observed, was interpreted as the result of an increasing magmatic component of the hydrothermal fluids, implying an increase of their flux. Indeed, such variation caused an increase of both the pore pressure within the rocks of the volcanic system and the amount of ascending fluids. Increased pore pressures gave rise to fracturing processes, while the increased fluid flux favoured resonance and vibration processes in cracks and conduits. Finally, a gradual temporal variation of the waveform of the hybrid events (one of the subclasses of long period events) was observed, likely caused by heating and drying of the hydrothermal system.     

Eruptive versus non-eruptive behaviour of large calderas: the example of Campi Flegrei caldera (southern Italy)

Caldera eruptions are among the most hazardous of natural phenomena. Many calderas around the world are active and are characterised by recurrent uplift and subsidence periods due to the dynamics of their magma reservoirs. These periods of unrest are, in some cases, accompanied by eruptions. At Campi Flegrei caldera (CFc), which is an area characterised by very high volcanic risk, the recurrence of this behaviour has stimulated the study of the rock rheology around the magma chamber, in order to estimate the likelihood of an eruption. This study considers different scenarios of shallow crustal behaviour, taking into account the earlier models of CFc ground deformation and caldera eruptions, and including recent geophysical investigations of the area. A semi-quantitative evaluation of the different factors that lead to magma storage or to its eruption (such as magma chamber size, wall-rock viscosity, temperature, and regional tectonic strain rate) is reported here for elastic and viscoelastic conditions. Considering the large magmatic sources of the CFc ignimbrite eruptions (400–2,000 km³) and a wall-rock viscosity between 10¹⁸ and 10²⁰ Pa s, the conditions for eruptive failure are difficult to attain. Smaller source dimensions (a few cubic kilometres) promote the condition for fracture (eruption) rather than for the flow of wall rock. We also analyse the influence of the regional extensional stress regime on magma storage and eruptions, and the thermal stress as a possible source of caldera uplift. The present study also emphasises the difficulty of distinguishing eruption and non-eruption scenarios at CFc, since an unambiguous model that accounts for the rock rheology, magma-source dimensions and locations and regional stress field influences is still lacking.     

Floating debris in the Ligurian Sea,north-western Mediterranean

Results from visual sightings of large floating debris are presented, taken in the Ligurian Sea, a sub-basin of the north-western Mediterranean Sea which belongs to the recently stated "Cetacean Sanctuary". Data have been collected during three oceanographic cruises, during the summer of 1997 and 2000. Results for the 1997 data suggest a debris density of the order of 15-25 objects km(-2), while for the 2000 data, a lower density of the order of 3-1.5 objects km(-2) is found. The difference between the two results appears statistically significant using simple tests. Possible reasons for the observed variability are discussed, including meteorological forcing, marine currents and debris input variability.     

Algorithms for GPS operation indoors and downtown

The proliferation of mobile devices and the emergence of wireless location-based services has generated consumer demand for availability of GPS in urban and indoor environments. This demand calls for enhanced GPS algorithms that accommodate high degrees of signal attenuation and multipath effects unique to the "urban channel." This paper overviews the market for location-based services and discusses algorithmic innovations that address challenges posed by urban environments. Electronic Publication     

Background discrimination capabilities of a heat and ionization germanium cryogenic detector

The discrimination capabilities of a 70 g heat and ionization Ge bolometer are studied. This first prototype has been used by the EDELWEISS dark matter experiment, installed in the Laboratoire Souterrain de Modane, for direct detection of WIMPs. Gamma and neutron calibrations demonstrate that this type of detector is able to reject more than 99.6% of the background while retaining 95% of the signal, provided that the background events distribution is not biased towards the surface of the Ge crystal. However, the 1.17 kg day of data taken in a relatively important radioactive environment show an extra population slightly overlapping the signal. This background is likely due to interactions of low energy photons or electrons near the surface of the crystal, and is somewhat reduced by applying a higher charge-collecting inverse bias voltage (−6 V instead of −2 V) to the Ge diode. Despite this contamination, more than 98% of the background can be rejected while retaining 50% of the signal. This yields a conservative upper limit of 0.7 event day⁻¹ kg⁻¹ keV_recoil⁻¹ at 90% confidence level in the 15–45 keV recoil energy interval; the present sensitivity appears to be limited by the fast ambient neutrons. Upgrades in progress on the installation are summarized.     

Sedimentary evolution of basins in mobile belts: examples from the Tertiary terrigenous sequences of the Peloritani Mountains (NE Sicily)

The Tertiary covers of the Peloritani Mountain Belt (NE Sicily) provide a complete stratigraphical record of tectonic events related to collision in the Central Mediterranean region. The tectonosedimentary evolution is inferred from interpretation of new field data and indicates various stages of polyphase deformation. The Peloritani Mountain Belt is composed mostly of crystalline units representing the active margin of the European Plate that was thrust over the descending African Plate during the Tertiary. Late Eocene-early Oligocene syn-orogenic deposition took place within a fore-arc basin located along the leading edge of the Peloritani Mountain Belt. From the late Oligocene to late Langhian, terrigenous deposition occurred throughout the mountain belt and extended into perched basins, located in southern areas. The basin was fed from the north, from source areas located in the hinterland of the orogenic belt. Deposition was controlled by a combination of active thrusting, regional subsidence and sea-level change. During the early Serravallian sudden tectonic inversion took place, associated with collapse of hinterland areas and uplift of former low-lying southern areas of the mountain belt. These processes were related to onset of opening of the Tyrrhenian Sea that was completed during the Serravallian-Tortonian, and resulted in the deposition of a northwestward prograding clastic fan, fed by source areas located in the southern area of the mountain belt. This setting characterized Messinian and Plio-Pleistocene deposition, and was controlled by both active tectonics and eustasy. The Recent evolution of the Peloritani Mountain Belt is characterized by major progressive uplift of the southern margins of the Tyrrhenian Basin, and local active subsidence related to downfaulting. Such processes resulted in the uplift of mid-Pleistocene fan-delta deposits and late Pleistocene marine terraces deposits to various altitudes above present sea-level.     

Structural setting and tectonic evolution of the Apennine Units of northern Calabria

A new structural–stratigraphic synthesis of the Apennine units of northern Calabria is presented. The Meso-Cenozoic successions are grouped into two tectonic units, named Pollino–Ciagola Unit (PCU) and Lungro–Verbicaro Unit (LVU), comprising terrains formerly attributed to five different tectonic units. FeMg carpholite and blue amphibole record HP–LT metamorphism in the LVU, followed by progressive decompression leading to final greenschist facies re-equilibration during dominantly extensional deformation. Final tectonic emplacement of the LVU over the PCU post-dated the metamorphism of the LVU and was accompanied by intense ductile deformation along zones of strain localisation in footwall rocks. All of the units were later affected by folding and minor thrusting during subsequent Apennine tectonics. To cite this article: A. Iannace et al., C. R. Geoscience 337 (2005).     

Organochlorine compounds in tissues of swordfish (Xiphias gladius) from Mediterranean Sea and Azores islands

Polychlorobiphenyls (PCB) and organochlorine (OC) pesticides are endocrine-disrupting chemicals (EDCs). The Italian Ministry of Environment has undertaken a program (1999-2001) to measure levels of contaminants in top marine predators and to develop sensitive biomarkers for the evaluation of toxicological risk in these species. In 1999, 15 swordfishes (Xiphias gladius) taken from the Mediterranean Sea along the Sicilian coast (Strait of Messina, Italy) and in the Atlantic Ocean along the Azores Islands, and analysed for 34 congeners of PCBs and 27 organochlorine (OC) pesticides in gonad, muscle, liver and blubber tissues. In the tissues of Mediterranean swordfishes the sum of the determined PCBs congeners ranged from 4.61 to 4651.17 ng g(-1) on fresh tissue basis. Among organochlorine pesticides DDE, DDT and DDD (TDE) predominated with an overall range of 2.37-4734.56 ng(-1) w.w. In particular p,p'-DDE had concentrations appearing up to 3900 ng(-1), with the highest values found in fatty tissues, such as blubber. In the liver of Azores Island swordfishes lower levels of summation PCBs (8.43-294.17 ng/g w.w.) and summation DDTs (<0.01-217.44 ng/g w.w.) were determined.     

Tectonic and sedimentary evolution of the Lower Pliocene Periadriatic foredeep in Central Italy

The Periadriatic foredeep (Italy) was generated by Neogene downbending of the Adria Plate under the Apennine Chain. The basin is filled with Plio-Pleistocene siliciclastic turbidites. Its substratum consists of the carbonate succession of the southwestern Adria Plate margin. The influence of the basin’s morphology on sedimentation and subsequent tectonic evolution is investigated in the Abruzzo sector of the foredeep (Cellino Basin). The substratum is composed of Messinian evaporites that dip towards the Apennines (W). A NNW component along the depocentral axis is divided into four blocks with different depths. The substratum was also affected by a Messinian extensional fault system, not involving the overlying Pliocene sequence. This morphology controlled the distribution of the turbidites in the lower part of the Cellino Basin. The Plio-Pleistocene compressional deformation of the foredeep produced an inner complex structure (Internal Structure), involving the foredeep substratum and an outer imbricate thrust system (Coastal Structure), detached over the faulted Messinian evaporites. This thrust system is parallel to the extensional faults, suggesting a strong influence of the substratum morphology on the development of the compressional structures. The overall structural setting was validated with a balanced cross-section. Out-of-sequence thrusting and non-coeval deformation within each thrust sheet characterize the local tectonic history.     

A physical analogue model to analyse interactions between tensile stresses and dissolution in carbonate slopes

A physical analogue model was developed to analyse the relationship between tensional states in rock masses, seepage and karst processes. Use was made of an experimental apparatus consisting of two hydraulic circuits realized by drilling two holes into each of two blocks of sampled limestone from the central Apennines (Italy). A static load (208.85 kg) was applied to one of the blocks in order to elicit tensile stresses within it. Physical and chemical monitoring data showed that the main process involved was temperature-dependent CaCO₃ dissolution. This process was more marked in the loaded block circuit, as Ca⁺⁺ concentration in circulated water reached 54 mg/L, whereas only 28 mg/L was reached in the unloaded one. The interaction between load and dissolution caused the observed opening of microcracks, as confirmed by further increase of water loss and by dilution in the loaded block circuit, resulting in a decrease of Ca⁺⁺ concentration. These findings were confirmed by recording additional water losses after increasing the load up to 445.05 kg. A finite difference numerical model showed that tensile stresses (max 20 kPa) within the loaded block were clustered at the intersection of the main joints with the flowpaths, thus representing points of preferential and accelerated dissolution.This study is part of a research project on analogical and numerical modelling for geological risk mitigation being conducted at CERI, Research Centre for Geological Risks of the University of Rome “La Sapienza” (Valmontone, Roma, Italy; http://www.ceri@uniroma1.it).