Seismotectonic models and CN algorithm: The case of Italy     

Giovanni Costa  Ivanka Orozova-Stanishkova  Giuliano Francesco Panza  Irina M. Rotwain 《Pure and Applied Geophysics》1996,147(1):119-130

The CN algorithm is utilized here both for the intermediate term earthquake prediction and to validate the seismotectonic model of the Italian territory. Using the results of the analysis, made through the CN algorithm and taking into account the seismotectonic model, three main areas, one for Northern Italy, one for Central Italy and one for Southern Italy, are defined. Two transition areas between the three main areas are delineated. The earthquakes which occurred in these two areas contribute to the precursor phenomena identified by the CN algorithm in each main area.  相似文献   

S-wave Velocity Models in the Scotia Sea Region, Antarctica, from Nonlinear Inversion of Rayleigh Waves Dispersion     

A. Vuan  R. Cazzaro  G. Costa  M. Russi  G. F. Panza 《Pure and Applied Geophysics》1999,154(1):121-139

—More than 60 events recorded by four recently deployed seismic broadband stations around Scotia Sea, Antarctica, have been collected and processed to obtain a general overview of the crust and upper mantle seismic velocities.¶Group velocity of the fundamental mode of Rayleigh waves in the period between 10 s to 30–40 s is used to obtain the S-wave velocity versus depth along ten different paths crossing the Scotia Sea region. Data recorded by two IRIS (Incorporated Research Institutions for Seismology) stations (PMSA, EFI) and the two stations of the OGS-IAA (Osservatorio Geofisico Sperimentale—Instituto Antarctico Argentino) network (ESPZ, USHU) are used.¶The Frequency-Time Analysis (FTAN) technique is applied to the data set to measure the dispersion properties. A nonlinear inversion procedure, "Hedgehog," is performed to retrieve the S-wave velocity models consistent with the dispersion data.¶The average Moho depth variation on a section North to South is consistent with the topography, geological observations and Scotia Sea tectonic models.¶North Scotia Ridge and South Scotia Ridge models are characterised by similar S-wave velocities ranging between 2.0 km/s at the surface to 3.2 km/s to depths of 8 km/s. In the lower crust the S-wave velocity increases slowly to reach a value of 3.8 km/s. The average Moho depth is estimated between 17 km to 20 km and 16 km to 19 km, respectively, for the North Scotia Ridge and South Scotia Ridge, while the Scotia Sea, bounded by the two ridges, has a faster and thinner crust, with an average Moho depth between 9 km and 12 km.¶On other paths crossing from east to west the southern part of the Scotia plate and the Antarctic plate south of South Scotia Ridge, we observe an average Moho depth between 14 km and 18 km and a very fast upper crust, compared to that of the ridge. The S-wave velocity ranges between 3.0 and 3.6 km/s in the thin (9–13 km) and fast crust of the Drake Passage channel. In contrast the models for the tip of the Antarctic Peninsula consist of two layers with a large velocity gradient (2.3–3.0 km/s) in the upper crust (6-km thick) and a small velocity gradient (3.0–4.0) in the lower crust (14-km thick).  相似文献   

Characterization of beryl (aquamarine variety) from pegmatites of Minas Gerais,Brazil   总被引：2，自引：0，他引：2  

R. R. Viana  H. Jordt-Evangelista  G. Magela da Costa  W. B. Stern 《Physics and Chemistry of Minerals》2002,29(10):668-679

Eight samples of the beryl variety aquamarine were selected from four pegmatites in the Governador Valadares and Araçuaí regions in northeastern Minas Gerais State, Brazil. These samples were fully characterized by chemical analysis, infrared and UV-visible spectroscopy, thermal analyses, and high-temperature X-ray diffraction (from room temperature up to 800 °C). Several physical and chemical properties of beryl were found to depend on the amount of water and ions residing in the structural channels. The thermal expansion coefficients from room temperature to about 800 °C are temperature-independent, with αa ? ?3.2 × 10^?6 ° C^?1 and αc ? ?8.7 × 10^?6 ° C^?1. The contraction of both a and c unit-cell parameters with increasing temperature and the shift of the infrared band centered at about 1200 cm^?1 were tentatively ascribed to interactions between channel water and the silicate rings.The color of beryl seems to be dictated by the relative proportions of Fe³⁺ in the octahedralsites and of fe²⁺ in the channels. Thus, deep-blue samples have little Fe³⁺, whereas greener samples have more Fe³⁺ or less channel Fe²⁺.  相似文献   

Total and methylmercury in a Brazilian estuary,Rio de Janeiro     

Kehrig HA  Costa M  Moreira I  Malm O 《Marine pollution bulletin》2002,44(10):1018-1023

Guanabara Bay, in Rio de Janeiro state, is impacted by organic matter, oil and heavy metals. The present study evaluated the total mercury (THg) and methylmercury (MeHg) concentrations and the MeHg to THg ratio (%MeHg) in water samples from different points of the bay and in 245 organisms of three different trophic levels sampled between 1990 and 2000. Dissolved mercury concentration in estuarine water samples ranged from 0.72 to 5.23 ngl(-1). THg and MeHg in mussel, ranging from 11.6 to 53.5 microg THg kg(-1) wet wt. and 4.5-21.0 microg MeHg kg(-1) wet wt., varied according to sampling point and water quality. Planktivorous fish and mussel presented similar MeHg concentrations, meanwhile THg in planktivorous fish were lower than in mussel. Carnivorous fish showed higher THg and MeHg concentrations (199.5 +/- 119.3, 194.7 +/- 112.7 microg kg(-1) wet wt. respectively) than organisms from other feeding habits and lower trophic levels. There was a significant difference in the %MeHg among trophic levels: mussel presented lower MeHg percentage (33%) than planktivorous fish (54%) and carnivorous fish (98%).  相似文献   

Sediment contamination in floodplains and alluvial terraces as an historical record of gold exploitation in the Carmo River basin,Southeast Quadrilátero Ferrífero,Minas Gerais,Brazil     

Adivane Terezinha Costa  Hermínio Arias Nalini  Paulo de Tarso Amorim Castro  Jorge Carvalho de Lena  Peter Morgenstern  Kurt Friese 《洁净——土壤、空气、水》2006,34(3):245-256

This paper describes the geochemistry of sediment samples placed in floodplains and alluvial terraces downstream from gold mines in the Carmo River basin, Quadrilátero Ferrífero, Minas Gerais, Brazil. The geochemistry signature Na₂O, K₂O, SiO₂, CaO, MgO, Al₂O₃, Fe₂O₃, TiO₂, P₂O₅, Mn, As, Cu, Zn, Ba, Ni, Cr, S, Co were analyzed in different facies from stratigraphic profiles. As, Cu, Zn, and Mn anomalies are mainly associated with the clayed facies deposited in floodplains and oxbow lakes, and with coarse‐sediment facies deposited in the channel. The facies were accumulated by the gold exploitation activity in the region. The contamination of As, Cu, and Zn was controlled by minerals such as iron oxides and hydroxides (hematite, magnetite, and mainly goethite), manganese oxides, and sulfide‐rich minerals. The As‐bearing sediments of the region characterize one of the most As contaminated area of Brazil. Their main source is associated with gold exploration in the last three centuries.  相似文献   

Comparison of the SFI peculiar velocities with the IRAS 1.2-Jy gravity field     

Luiz N. da Costa  Adi Nusser  Wolfram Freudling  Riccardo Giovanelli  Martha P. Haynes  John J. Salzer  & Gary Wegner 《Monthly notices of the Royal Astronomical Society》1998,299(2):425-432

We present a comparison between the peculiar velocity fields measured from a recently completed l -band Tully–Fisher survey of field spirals (SFI) and that derived from the IRAS 1.2-Jy redshift survey galaxy distribution. The analysis is based on the expansion of these data in redshift space using smooth orthonormal functions, and is performed using low- and high-resolution expansions, with an effective smoothing scale which increases almost linearly with redshift. The effective smoothing scales at 3000 km s⁻¹ are 1500 and 1000 km s⁻¹ for the low- and high-resolution filters. The agreement between the high- and low-resolution SFI velocity maps is excellent. The general features in the filtered SFI and IRAS velocity fields agree remarkably well within 6000 km s⁻¹. This good agreement between the fields allows us to determine the parameter β = Ω^0.6 / b , where Ω is the cosmological density parameter, and b is the linear biasing factor. From a likelihood analysis on the SFI and IRAS modes we find that β = 0.6 ± 0.1, independently of the resolution of the modal expansion. For this value of β, the residual fields for the two filters show no systematic variations within 6000 km s⁻¹. Most remarkable is the lack of any coherent, redshift-dependent dipole flow in the residual field.  相似文献   

Palynostratigraphy of some Middle Eocene sections from the Hampshire Basin (England)     

Lucy I. Costa  Charles Downie  Geoffrey L. Eaton 《Proceedings of the Geologists' Association. Geologists' Association》1976,87(3):273-284

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Biostratigraphic ages of tertiary basalts on the East Greenland continental margin and their relationship to plate separation in the Northeast Atlantic     

N.J. Soper  C. Downie  A.C. Higgins  L.I. Costa 《Earth and Planetary Science Letters》1976,32(2):149-157

Palynological evidence indicates that the 4?5 × 10⁵ km³ pile of tholeiitic basalts on the central east Greenland coast was erupted in latest Palaeocene (late Landenian) and earliest Eocene (early Ypresian) time. Assignment of a precise numerical age of this interval is not yet possible, but it is evident that the eruptive episode was completed within about 3 m.y. The effusion rate was at least an order of magnitude faster than the current Icelandic rate. Marine horizons at the base and top of the pile show that its build-up was accompanied by concomitant crustal depression. It is argued that this major volcanic episode marks the initiation of plate separation between Greenland and northwest Europe. Implications with regard to spreading chronology and the magnetic polarity time scale are discussed.  相似文献   

Interpretation of temporal features in an unusual X-ray and microwave burst     

A. L. Mackinnon  J. E. R. Costa  P. Kaufmann  B. R. Dennis 《Solar physics》1986,104(1):191-198

Observations are briefly discussed of an event in which microwave and hard X-ray emissions were not correlated in the accepted way. Two impulsive peaks of roughly equal intensity were observed at three different microwave frequencies. The hard X-ray peaks accompanying these, however, differ in intensity by almost two orders of magnitude. Various possible interpretations of this burst are discussed, in the context of familiar models of these emissions. The most likely explanation is that the electron spectrum in the first burst has a break at about 350 keV. General implications for interpretation of X-rays and microwaves are discussed.Proceedings of the Workshop on Radio Continua during Solar Flares, held at Duino (Trieste), Italy, 27–31 May, 1985.  相似文献   

Conservation Priority Index for Estuarine Fish (COPIEF)     

Paulo Branco  Jos Lino Costa  Pedro Raposo de Almeida 《Estuarine, Coastal and Shelf Science》2008,80(4):581-588

Public awareness regarding environmental issues has increased in recent decades. The increasing number of impact assessment studies, management and conservation plans, as well as ecological monitoring studies, demand new and more efficient techniques. Indices are an important tool to aid biologists in these studies and should allow an easier comprehension of the data by managers, decision-makers and the general public. This study presents the first multi-metrical index able to establish a hierarchical ordination of the conservation priority of the estuarine fish species using 72 species from 16 estuarine systems (W and S coasts of Portugal). The index is composed of 10 metrics, comprising species life traits, distribution and population trends. The information needed to score each metric was gathered from the published literature and the index validation was done by external means. This methodology allowed the definition of those fish species most in need of conservation planning, and those less prone to extinction in Portuguese estuarine systems. The proposed index fills a gap in our knowledge and provides a useful tool to the scientific community and to the decision-makers, being a breakthrough in the field of conservation planning of estuarine fish species.  相似文献