Water‐bottom multiple attenuation by Kirchhoff extrapolation

Despite being less general than 3D surface‐related multiple elimination (3D‐SRME), multiple prediction based on wavefield extrapolation can still be of interest, because it is less CPU and I/O demanding than 3D‐SRME and moreover it does not require any prior data regularization. Here we propose a fast implementation of water‐bottom multiple prediction that uses the Kirchhoff formulation of wavefield extrapolation. With wavefield extrapolation multiple prediction is usually obtained through the cascade of two extrapolation steps. Actually by applying the Fermat’s principle (i.e., minimum reflection traveltime) we show that the cascade of two operators can be replaced by a single approximated extrapolation step. The approximation holds as long as the water bottom is not too complex. Indeed the proposed approach has proved to work well on synthetic and field data when the water bottom is such that wavefront triplications are negligible, as happens in many practical situations.     

Permian continental basins in the Southern Alps (Italy) and peri-mediterranean correlations

The Late Carboniferous to Permian continental successions of the Southern Alps can be subdivided into two main tectono-sedimentary Cycles, separated by a marked unconformity sealing a Middle Permian time gap, generally estimated at over 10 Ma. The lower cycle (1), between the Variscan crystalline basement and the Early Permian, is mainly characterised by fluvio-lacustrine and volcanic deposits of calc-alkaline acidic-to-intermediate composition, which range up to a maximum thickness of more than 2,000 m. The upper cycle (2), which is devoid of volcanics, is mostly dominated through the Mid?–Late Permian by alluvial sedimentation which covered the previous basins and the surrounding highs, giving rise to the subaerial Verrucano Lombardo-Val Gardena (Gröden) red-beds, up to about 800 m thick. The palaeontological record from the terrigenous deposits of both the above cycles consists mainly of macro- and microfloras and tetrapod footprints. The age of the continental deposits is widely discussed because of the poor chronological significance of a large number of fossils which do not allow reliable datings; however, some sections are also controlled by radiometric calibrations. The comparison with some selected continental successions in southern Europe allows to determine their evolution and set up correlations. A marked stratigraphic gap shows everywhere between the above-mentioned Cycles 1 and 2. As in the Southern Alps, the gap reaches the greatest extent during the Mid-Permian, near the Illawarra Reversal geomagnetic event (265 Ma). In western Europe, however, such as in Provence and Sardinia, the discussed gap persists upwardly to Late Permian and Early Triassic or slightly younger times, i.e. to the onset of the “Alpine sedimentary Cycle”, even though in northeastern Spain (Iberian Ranges, Balearic Islands) this gap results clearly interrupted by late Guadalupian–Lopingian deposits. The above two major tectonosedimentary cycles reflect, in our view, two main geodynamic events that affected the southern Europe after the Variscan orogenesis: the Late Carboniferous–Early Permian transformation of the Gondwana–Eurasia collisional margin into a diffuse dextral transform margin and the Middle–Late Permian opening of the Neotethys Ocean, with the onset of a generalised extensional tectonic regime and the progressive westward marine ingression.     

Natural and anthropogenic sources of total suspended particulate and their contribution to the formation of black crusts on building stone materials of Catania (Sicily)

Blackening and disaggregation of exposed surfaces of stone monuments are well-known effects of stone decay taking place in polluted urban environments all over the world. This paper aims to assess the contribution of natural and anthropogenic sources of total suspended particulate (TSP) causing permanent damage (black crusts) to the stone monuments of Catania (Sicily), one of the most popular ??cities of art?? of southern Italy. Atmospheric pollution of Catania, a typical Mediterranean coastal town, is mainly contributed by vehicle exhaust emissions rather than industrial ones. Episodically, the city also suffers gaseous and ash emissions (plumes) from the nearby Mount Etna volcano. Thus, to discriminate between natural and anthropogenic contributions to stone decay on Catania monuments, black crusts and TSP were sampled within the urban area and subjected to specific analytical procedures (optical microscopy, X-ray powder diffraction, Fourier transformed infrared spectroscopy, scanning electron microscopy equipped with energy dispersive spectrometry, ionic chromatography and dual inlet mass spectrometry). Mineralogical, chemical and isotopic characterization of black crusts and TSP provided new insights concerning the partition of sulfate sources in this particular urban context. The influence of Mount Etna emissions on both TSP and black crusts compositions was shown. Nevertheless, the key role of anthropogenic sources in the total sulfate budget was confirmed, while sea spray and volcanic emissions were found to make subordinate contributions. Quantitative data useful for the identification of the threshold pollution levels for preventive conservation of Catania monuments were obtained.     

Effects of air temperature on the cyclic behavior of elastomeric seismic isolators

The mechanical properties of elastomers can change significantly due to air temperature variations. In particular, prolonged exposure to subzero temperatures can result in rubber crystallization, with a considerable increase in the shear stiffness of the material. As a result, the seismic response of structures with elastomeric isolators can be strongly influenced by air temperature. Current seismic codes, indeed, require an upper and lower bound analysis, using suitable modification factors, to account for the changes in the cyclic behavior of elastomeric isolators due to air temperature variations. In this study, the sensitivity of the cyclic behavior of elastomeric isolators to air temperature variations is investigated based on the experimental results of an extensive test program on six different elastomeric compounds for seismic isolators, characterized by a shear modulus ranging from 0.5 to 1.2 MPa at 100% shear strain and 20°C. The cyclic tests have been performed on small-size specimens, subjected to shear strain amplitudes and frequency of loading typical for elastomeric seismic isolators, at seven different air temperatures, ranging from 40 to −20°C. The effects of rubber crystallization due to prolonged exposure to low-temperatures have been also investigated. A finite element model for the evaluation of the temperature contour map inside a full-size elastomeric isolator exposed to low air temperatures has been also developed. In the paper, the experimental outcomes are compared with the modification factors provided by the current seismic codes to account for the temperature effects on the mechanical properties of elastomeric isolators.     

A performance-based adaptive methodology for the seismic evaluation of multi-span simply supported deck bridges

A performance-based adaptive methodology for the seismic assessment of highway bridges is proposed. The proposed methodology is based on an Inverse (I), Adaptive (A) application of the Capacity Spectrum Method (CSM), with the capacity curve of the bridge derived through a Displacement-based Adaptive Pushover (DAP) analysis. For this reason, the acronym IACSM is used to identify the proposed methodology. A number of Performance Levels (PLs), for which the seismic vulnerability and seismic risk of the bridge shall be evaluated, are identified. Each PL is associated to a number of Damage States (DSs) of the critical members of the bridge (piers, abutments, joints and bearing devices). The IACSM provides the earthquake intensity level (PGA) corresponding to the attainment of the selected DSs, using over-damped elastic response spectra as demand curves. The seismic vulnerability of the bridge is described by means of fragility curves, derived based on the PGA values associated to each DS. The seismic risk of the bridge is evaluated as convolution integral of the product between the fragility curves and the seismic hazard curve of the bridge site. In this paper, the key aspects and basic assumptions of the proposed methodology are presented first. The IACSM is then applied to nine existing simply supported deck bridges, characterized by different types of piers and bearing devices. Finally, the IACSM predictions are compared with the results of nonlinear response time-history analysis, carried out using a set of seven ground motions scaled to the expected PGA values.     

Tectonic and eustatic controls on Pliocene accommodation space along the front of the southern Apennine thrust‐belt (Basilicata,southern Italy)

The stratigraphical organization of the Pliocene thrust‐top deposits cropping out at the front of the Southern Apennine thrust‐belt has been debated for a long time taking a great importance in the context of the geodynamics of the Central Mediterranean area. During this time, spreading episodes in the Apennine backarc zone alternate with important phases of overthrusting in the thrust‐belt. As a consequence, the Pliocene succession appears to be arranged in a series of stacked units, recording the poliphase tectonic history that leads to the building of the front of the southern Apennine thrust‐belt. Although there is not yet an accordance on the nature and position of the main unconformities bounding the thrust‐top units, all authors agree that the creation of new accommodation space is mainly ruled by contractional tectonics consequent to the eastward nappe propagation according to the Apennine vergence polarity. A detailed geological survey, carried out along a large portion of southern Apennine thrust‐belt front, running south of the Vulture volcano, allowed the collecting of new data concerning the basinal‐formation mechanisms acting during the sedimentation of Pliocene deposits. From this analysis, it is clear that even if contractional tectonics is the predominant factor controlling the creation or destruction of accommodation space, other mechanisms, as well as wedge uplift‐related extensional tectonics and eustasy, could have also played a significant role in the basin accommodation. In order the considered sector of southern Apennines can provide an useful example about the complex phenomena occurring at mountain belt front where the accommodation space results from a concomitance of eustatic and tectonic factors mainly linked to the accretionary wedge activity.     

Design Aspects of Grazing Angle Multilayer Mirrors for Soft γ-Rays

If sensitive enough, future missions for nuclear astrophysics will be a great help in understanding supernovae explosions. In contrast to coded-mask instruments, both crystal diffraction lenses and grazing angle mirrors offer a possibility to construct a sensitive instrument to detect γ-ray lines in supernovae. We report on possible implementations of grazing angle mirrors and simulations carried out to determine their performance.     

Volcanic soil formation in Calabria (southern Italy): The Cecita Lake geosol in the late Quaternary geomorphological evolution of the Sila uplands

This paper focuses on the main morphological, physical, chemical and mineralogical features of an andic-like soil, widely outcropping in the Sila upland plateau of Calabria (southern Italy), and its potential role in tephrostratigraphy. A multidisciplinary and multiscale approach allowed identification of this soil as a “masked” distal archive of volcanic products, developed on granite rocks and sediments with a coeval pyroclastic input during pedogenesis. The study demonstrates that the contribution of volcanic parent materials can be successfully hypothesized and assessed even in the absence, limited extent or poor preservation of primary eruptive products. The soil has an Andisol-like appearance, despite laboratory data that do not match the entire suite of diagnostic criteria for the Andisol taxonomic order. Geomorphological, stratigraphic and pedologic results, coupled with tephrostratigraphic and radiometric data, concur to suggest a Late Pleistocene(?) to Holocene age of the Andisol-like soil. In particular, the rhyolitic chemical composition of small-sized glass fragments (identified by SEM–EDS analyses) indicates soil genesis contributed by volcanic ash, probably sourced from Aeolian Arc explosive activity spanning the last 30 ka. Accordingly, the evidence of limited relict clay illuviation and the specific type of pedogenesis allowing the development of andic properties (in turn related to the neoformation of clay minerals from the weathering of volcanic glass) are consistent with a climatic shift from a seasonally-contrasted to a constantly humid pedoenvironment. This change can be ascribed to the Lateglacial(?) or Early–Middle Holocene to Late Holocene transition. Calibrated AMS ¹⁴C dates performed on charcoal fragments sampled from three representative soil profiles, provide Late Holocene ages (3136 ± 19, 343 ± 16 and 92 ± 24 yr BP), in accord with archaeological finds. On the basis of the consistent stratigraphic position, lateral continuity and wide extent, the soil can be considered a good pedostratigraphic marker in the Sila highlands and is informally defined as the “Cecita Lake geosol”. It supplies valuable time constraints for the underlying (occasionally overlying) deposits and/or soils. Moreover, it allows regional-scale morphostratigraphic correlations and detailed reconstruction of Late Pleistocene–Holocene geomorphic events in Calabria, a very suitable region for distal tephra deposition in the central Mediterranean peri-volcanic area. The effects of high-energy volcanic eruptions are interfingered with or superimposed by other geomorphic processes and climatic or anthropogenic signals.     

Lava flow hazard at Nyiragongo Volcano,DRC

Mt. Nyiragongo is one of the most dangerous volcanoes in the world for the risk associated with the propagation of lava flows. In 2002 several vents opened along a huge system of fractures, pouring out lava which reached and destroyed a considerable part of Goma, a town of about 500,000 inhabitants on the shore of Lake Kivu. In a companion paper (Favalli et al. in Bull Volcanol, this issue, 2008) we employed numerical simulations of probable lava flow paths to evaluate the lava flow hazard on the flanks of the volcano, including the neighbouring towns of Goma (DRC) and Gisenyi (Rwanda). In this paper we use numerical simulations to investigate the possibility of significantly reducing the lava flow hazard in the city through the construction of protective barriers. These barriers are added to the DEM of the area as additional morphological elements, and their effect is evaluated by repeating numerical simulations with and without the presence of barriers. A parametric study on barrier location, size, shape and orientation led to the identification of barriers which maximize protection while minimizing their impact. This study shows that the highest hazard area corresponding to eastern Goma, which was largely destroyed by lava flows in 2002, cannot be effectively protected from future lava flows towards Lake Kivu and should be abandoned. On the contrary, the rest of the town can be sheltered from lava flows by means of two barriers that deviate or contain the lava within the East Goma sector. A proposal for the future development of the town is formulated, whereby “new” Goma is completely safe from the arrival of lava flows originating from vents outside its boundaries. The proposal minimizes the risk of further destruction in town due to future lava flows.