Attenuation tomography: An application to gas-hydrate and free-gas detection   总被引：1，自引：0，他引：1  

Giuliana Rossi  Davide Gei  Gualtiero Böhm  Gianni Madrussani  José M. Carcione 《Geophysical Prospecting》2007,55(5):655-669

We estimate the quality factor (Q) from seismic reflections by using a tomographic inversion algorithm based on the frequency‐shift method. The algorithm is verified with a synthetic case and is applied to offshore data, acquired at western Svalbard, to detect the presence of bottom‐simulating reflectors (BSR) and gas hydrates. An array of 20 ocean‐bottom seismographs has been used. The combined use of traveltime and attenuation tomography provides a 3D velocity–Q cube, which can be used to map the spatial distribution of the gas‐hydrate concentration and free‐gas saturation. In general, high P‐wave velocity and quality factor indicate the presence of solid hydrates and low P‐wave velocity and quality factor correspond to free‐gas bearing sediments. The Q‐values vary between 200 and 25, with higher values (150–200) above the BSR and lower values below the BSR (25–40). These results seem to confirm that hydrates cement the grains, and attenuation decreases with increasing hydrate concentration.  相似文献   

Imposex levels and concentrations of organotin compounds (TBT and its metabolites) in Nassarius nitidus from the Lagoon of Venice     

Bruno Pavoni  Elena Centanni  Sara Valcanover  Marco Fasolato  Silvia Ceccato  Davide Tagliapietra 《Marine pollution bulletin》2007,55(10-12):505

Specimens of Nassarius nitidus were collected in seven stations of the Venice Lagoon to assess the levels of tributyltin (TBT) and its metabolites monobutyltin and dibutyltin in the tissues and monitor their effect on organisms, in particular the phenomenon of imposex (superimposition of male sexual characteristics on females). The following values of population indices were found: vas deferens sequence: 1.2 ± 0.7–4.0 ± 0.5; relative penis length: 6–47%. The least impacted station was situated in the northern part of the Lagoon, where females without imposex were found and Butyltin (BuTs) concentrations in the organisms (average sum of BuTs = 43 ± 14 ng Sn g⁻¹ w.) were significantly lower than in the other stations (range of average sum of BuTs: 101 ± 22–217 ± 27 ng Sn g⁻¹ d.w.). Population indices were found to be related to the TBT content in the tissues. In particular VDSI had a significant logarithmic correlation: r = 0.95, n = 8, p < 0.05.  相似文献   

Melt inclusions in detrital spinel from the SE Alps (Italy–Slovenia): a new approach to provenance studies of sedimentary basins     

Davide Lenaz  Vadim S. Kamenetsky  Anthony J. Crawford  Francesco Princivalle 《Contributions to Mineralogy and Petrology》2000,139(6):748-758

Detrital spinel is a widespread heavy mineral in sandstones from the Maastrichtian–Middle Eocene sedimentary basins in the SE Alps. Chemistry of detrital spinels from the Claut/Clauzetto and Julian Basins (N Italy and NW Slovenia) is used to constrain petrological and geochemical affinities and tectonic provenance of the source rocks. In addition, we have analysed melt inclusion compositions in the detrital volcanic spinels to better constrain the nature of their parental magmas. This is the first study of melt inclusions in detrital spinels. Two principal compositional groups of detrital spinels are recognised based on their TiO₂ and Fe²⁺/Fe³⁺; one derived from peridotites, the other from basaltic volcanics. Peridotitic spinels are more abundant and have TiO₂ < 0.2 wt% and high Cr/Cr + Al (40–90), characteristic of suprasubduction zone harzburgites. Significant chemical variations among volcanic spinels (TiO₂ up to 3 wt%, Al₂O₃ 12–44 wt%) suggest multiple sources, with geochemically distinct characteristics, including MORB-type and backarc basin basalts, subduction-related magmas and tholeiites produced during early continental rifting. Compositions of homogenised melt inclusions in spinels with TiO₂ > 0.2 better distinguish the differences between the compositions of their host spinels and help to further clarify the geodynamic provenance of extrusive source rocks. Several compositional groups of melt inclusions have been recognised and represent diverse magmatism of marginal basins, including MORB- and subduction-related geochemical types, as well as magmas characteristic of early continental rifting. These results, combined with the data on regional ophiolitic complexes and tectonic reconstructions favour the Internal Dinarides of Yugoslavia as a possible source area for the SE Alps sediments. Received: 20 January 2000 / Accepted: 25 April 2000  相似文献   

Compton dragged gamma-ray bursts: the spectrum     

Gabriele Ghisellini  Davide Lazzati  Annalisa Celotti  Martin J. Rees 《Monthly notices of the Royal Astronomical Society》2000,316(4):L45-L49

Recently several studies have jointly analysed data from different cosmological probes with the motivation of estimating cosmological parameters. Here we generalize this procedure to allow freedom in the relative weights of various probes. This is done by including in the joint χ ² function a set of 'hyper-parameters', which are dealt with using Bayesian considerations. The resulting algorithm, which assumes uniform priors on the log of the hyper-parameters, is very simple: instead of minimizing     (where     is per data set j ) we propose to minimize     (where N _j is the number of data points per data set j ). We illustrate the method by estimating the Hubble constant H ₀ from different sets of recent cosmic microwave background (CMB) experiments (including Saskatoon, Python V, MSAM1, TOCO and Boomerang ). The approach can be generalized for combinations of cosmic probes, and for other priors on the hyper-parameters.  相似文献   

Turbulence in the Stable Boundary Layer at Higher Richardson Numbers   总被引：1，自引：1，他引：0  

Enrico Ferrero  Lihong Quan  Davide Massone 《Boundary-Layer Meteorology》2011,139(2):225-240

We present some algebraic and numerical simulations of the stable boundary layer. We also discuss the problem of the existence of a critical Richardson number (Ri), beyond which the turbulence is suppressed. We compare the results of a second-order algebraic model with those of a third-order numerical model and, to this purpose, numerical simulations of a wind-tunnel flow, which is characterized by various Richardson numbers, were performed. As far as the second-order model is concerned, solutions, for the Richardson number greater than any critical value, can be obtained by modifying the time scales of the second-order equation pressure correlation terms in order to account for a buoyancy damping factor. We show that using a third-order model allows the same results (no critical Richardson number) to be obtained without modifications to the time scales. It is suggested that the non-locality, accounted for by the third-order moments, could allow the turbulence to persist also for Ri > 1.  相似文献   

Analysis with C- and X-band satellite SAR data of the Portalet landslide area   总被引：1，自引：0，他引：1  

Gerardo Herrera  Davide Notti  Juan Carlos Garc��a-Davalillo  Oscar Mora  Geraint Cooksley  M��nica S��nchez  Alain Arnaud  Michele Crosetto 《Landslides》2011,8(2):195-206

This paper describes the use of the Stable Point Network technique, a Persistent Scatterer Interferometry SAR technique, for the analysis of the Portalet landslide area (Central Pyrenees, Spain). For this purpose, different SAR datasets acquired by ERS-1, ERS-2, ENVISAT and TerraSAR-X satellites have been analysed. The use of different SAR images acquired by satellite radar sensors operating at different microwave lengths has allowed for a comparative assessment and illustration of the advantages and disadvantages of these satellites for landslide detection and monitoring. In the introduction, differential interferometry and the study area are briefly described. Then the specifics of the SPN processing and the results of the different datasets are described and compared. In Analysis of the results: the Portalet landslide area, the Portalet landslide area is introduced and the radar displacement measurements are analysed with available geo-information data. Additionally, X-band measurements are compared with those gathered by a ground-based SAR for a previous project. Finally, the most relevant conclusions of this work are discussed.  相似文献   

Seismic modelling study of a subglacial lake     

José M. Carcione  Davide Gei 《Geophysical Prospecting》2003,51(6):501-515

We characterize the seismic response of Lake Vostok, an Antarctic subglacial lake located at nearly 4 km depth below the ice sheet. This study is relevant for the determination of the location and morphology of subglacial lakes. The characterization requires the design of a methodology based on rock physics and numerical modelling of wave propagation. The methodology involves rock-physics models of the shallow layer (firn), the ice sheet and the lake sediments, numerical simulation of synthetic seismograms, ray tracing, τ–p transforms, and AVA analysis, based on the theoretical reflection coefficients. The modelled reflection seismograms show a set of straight events (refractions through the firn and top-ice layer) and the two reflection events associated with the top and bottom of the lake. Theoretical AVA analysis of these reflections indicates that, at near offsets, the PP-wave anomaly is negative for the ice/water interface and constant for the water/sediment interface. This behaviour is shown by AVA analysis of the synthetic data set. This study shows that subglacial lakes can be identified by using seismic methods. Moreover, the methodology provides a tool for designing suitable seismic surveys.  相似文献   

The role of photon scattering in shaping the light curves and spectra of γ-ray bursts     

Davide Lazzati 《Monthly notices of the Royal Astronomical Society》2002,337(4):1426-1434

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The polarization of afterglow emission reveals γ-ray bursts jet structure     

Elena M. Rossi  Davide Lazzati  Jay D. Salmonson  Gabriele Ghisellini 《Monthly notices of the Royal Astronomical Society》2004,354(1):86-100

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A multidisciplinary investigation of deep-seated landslide reactivation triggered by an extreme rainfall event: a case study of the Monesi di Mendatica landslide,Ligurian Alps     

Notti  Davide  Wrzesniak  Aleksandra  Dematteis  Niccolò  Lollino  Piernicola  Fazio  Nunzio Luciano  Zucca  Francesco  Giordan  Daniele 《Landslides》2021,18(7):2341-2365

Landslides - In November 2016, an extreme rainfall event affected the Ligurian Alps (NW Italy). Consequently, several landslides and debris flows occurred in the upper Tanarello stream basin. In...  相似文献