Structure and nuclear density distribution in the cheralite—CaTh(PO4)2: studies of its behaviour under high pressure (36?GPa)     

Philippe E. Raison  Stephen Heathman  Gilles Wallez  Carmen E. Zvoriste  Denis Bykov  Ga?l Ménard  Emmanuelle Suard  Karin Popa  Nicolas Dacheux  Rudy J. M. Konings  Roberto Caciuffo 《Physics and Chemistry of Minerals》2012,39(8):685-692

The crystal structure of the cheralite—CaTh(PO₄)₂—has been revisited by neutron diffraction and its behaviour under high pressure investigated by X-ray diffraction up to 36?GPa. The neutron diffraction data at ambient pressure gave a more accurate determination of the Ca/Th cation position than previous XRD data, taking advantage that the neutron scattering lengths of calcium and thorium are of same order of magnitude. The nuclear density distribution was also determined using the maximum entropy method (MEM) confirming that the two cations are not located at the same position in the unit cell but are slightly displaced from one another along a specific direction in order to minimize the electrostatic repulsion with the surrounding phosphorus atoms. At high pressure, the compound did not show any phase transition or amorphization. From the evolution of the unit-cell volume as a function of the pressure, the zero-pressure bulk modulus B₀ and its pressure derivative B₀ ^′ have been determined by fitting the experimental compressibility curve to the Birch–Murnaghan equation of state. The results are B₀?=?140(2) GPa and B ₀ ^′ ?=?4.4(4) GPa.  相似文献   

Glaucony from the Cretaceous of the Sierra de Guadarrama (Central Spain) and its application in a sequence-stratigraphic context   总被引：1，自引：0，他引：1  

Alessandro Amorosi  Roberto Guidi  Ramon Mas  Elisa Falanga 《International Journal of Earth Sciences》2012,101(2):415-427

Detailed sedimentological and geochemical analyses of Upper Cretaceous glaucony-bearing deposits from the middle portion of the Castro de Fuentidueña Formation, in Central Spain, enable identification of a multiphase history of glaucony accumulation. Despite its relatively high maturity (K₂O > 7%), glaucony from the transgressive subtidal sandstones has anomalously low concentration in the host rock (generally <10%), suggesting remobilization from a different source. The remarkable thickness of the glaucony-bearing horizons, concurrently with concentration of glaucony in laminae, small size, and high degree of roundness and sorting provide further evidence for an allochthonous origin of the green grains. In contrast, authigenic glaucony from the overlying offshore clays exhibits higher abundance (up to 45%) and lower maturity (K₂O < 7%) and is interpreted to have formed in situ. Allochthonous glaucony originally developed in more distal areas during a prolonged period of sediment starvation. The green grains were then swept away from their place of origin and concentrated into tidal bars and channels within the upper transgressive systems tract of the third-order depositional sequence. Maximum concentration of autochthonous glaucony is recorded at the transition from tidal-influenced to offshore deposits: this glaucony, which is relatively less evolved due to lower time available for maturation, is interpreted to reflect the turnaround from transgressive to highstand conditions, marking the condensed section of the depositional sequence. As postulated by previous sequence-stratigraphic models, this study documents that allochthonous glaucony can be widespread throughout the transgressive systems tract (TST), while the condensed section (CS) typically hosts autochthonous glaucony. Contrary to the existing literature, however, this study shows that glaucony from the TST may be even more mature than glaucony from the CS, if enough time for maturation during transgression is allowed before the ultimate concentration of the green grains. Identification of spatial and temporal characteristics of glaucony, thus, is critical to a reliable sequence-stratigraphic interpretation of the glaucony-bearing deposits.  相似文献   

The 29 September 2009 Samoa Islands Tsunami: Simulations Based on the First Focal Mechanism Solutions and Implications on Tsunami Early Warning Strategies     

Roberto Tonini  Alberto Armigliato  Stefano Tinti 《Pure and Applied Geophysics》2011,168(6-7):1113-1123

The tsunamigenic earthquake (Mw?=?8.1) that occurred on 29 September 2009 at 17:48 UTC offshore of the Samoa archipelago east of the Tonga trench represents an example of the so-called ??outer-rise?? earthquakes. The areas most affected were the south coasts of Western and American Samoa, where almost 200 people were killed and run-up heights were measured in excess of 5?m at several locations along the coast. Moreover, tide gauge records showed a maximum peak-to-peak height of about 3.5?m near Pago Pago (American Samoa) and of 1.5?m offshore of Apia (Western Samoa). In this work, different fault models based on the focal mechanism solutions proposed by Global CMT and by USGS immediately after the 2009 Samoan earthquake are tested by comparing the near-field recorded signals (three offshore DART buoys and two coastal tide gauges) and the synthetic signals provided by the numerical simulations. The analysis points out that there are lights and shadows, in the sense that none of the computed tsunamis agrees satisfactorily with all the considered signals, although some of them reproduce some of the records quite well. This ??partial agreement?? and ??partial disagreement?? are analysed in the perspective of tsunami forecast and of Tsunami Early Warning System strategy.  相似文献   

SLA–chlorophyll-a variability and covariability in the Algero-Provençal Basin (1997–2007) through combined use of EOF and wavelet analysis of satellite data     

Antonio Olita  Alberto Ribotti  Roberto Sorgente  Leopoldo Fazioli  Angelo Perilli 《Ocean Dynamics》2011,61(1):89-102

Data reduction and signal decomposition techniques have been applied to a large bio-physical remotely sensed dataset covering the decade 1997–2007. The aim was the estimation of the spatial (basin and sub-basin scales) and temporal (seasonal and interannual) variability of sea level anomalies and chlorophyll-a concentration in the Algero-Provençal Basin, as well as the study of their covariability. Empirical orthogonal functions, wavelet analysis, singular value decomposition and correlation maps have been successfully used to individuate the patterns of (co)variability of the investigated fields. The seasonal variability of the phytoplanktonic biomass is divided in two distinct modes, timewise and spacewise separated. Positive interannual events are related to anomalies in 1999 and 2005, while the main (negative) anomaly is that of summer 2003, associated to the European 2003 heatwave. The analysis of the sea level anomalies shows a minimum in the formation of anticyclonic Algerian eddies during that period. The largest anticorrelation between sea level anomalies and phytoplanktonic biomass is found in the central zone of the basin, suggesting a clear biological response to the shoaling/deepening of the isopycnae and so to the nutrient injection into the euphotic layer. The analysis suggests that the driver of the variability of the nutricline depth in this central area is the displacement (seasonal) of the North Balearic Front and the formation/action of the frontal eddies.  相似文献   

Engineering ground motion record selection in the ITalian ACcelerometric Archive   总被引：1，自引：1，他引：0  

Iunio Iervolino  Carmine Galasso  Roberto Paolucci  Francesca Pacor 《Bulletin of Earthquake Engineering》2011,9(6):1761-1778

This paper introduces REXELite, an internet version of REXEL, a software for automatic selection of ground motion suites for nonlinear dynamic analysis of structures. REXELite was developed with the aim of integrating an advanced earthquake records’ repository, such as the ITalian ACcelerometric Archive (ITACA), with a tool to define seismic input for engineering seismic analysis according to international standards (with priority to Europe). In fact, REXELite allows to define target design spectra according either to Eurocode 8 or to the Italian building code, and to search ITACA for suitable sets of seven records (comprised of one or two horizontal ground motion components) matching such target spectra: on average, in a user-specified period range, and with the desired tolerance. The records in the set also have, individually and according to some criteria, the most similar spectral shape with respect to that of the code. Selection options include magnitude, source-to-site distance, soil conditions and, if desired, linear scaling of records to reduce further record-to-record variability of the selected suite.  相似文献   

Refractor velocity analysis: a signal processing procedure     

Roberto de Franco 《Geophysical Prospecting》2011,59(3):432-454

This paper presents a signal processing procedure to perform refractor velocity analysis. The procedure enables one to obtain the seismic velocity from the refracted wavefield without the picking of refracted arrival times. Two processing procedures are derived, one starting from a seismic interferometric approach and another, from the conventional reciprocal method and generalized reciprocal method approaches. The theoretical equivalence of the two approaches is also demonstrated. The proposed processing procedure is applied to synthetic data in order to test the influence of some procedural parameters and its capability to reconstruct a known velocity model starting from refracted signals, without and with perturbations, in arrival times and noise; finally, it is applied to a field data set.  相似文献   

Diatom quantification and their distribution with salinity brines in coastal sediments of Terra Nova Bay (Antarctica)     

Baldi F  Facca C  Marchetto D  Nguyen TN  Spurio R 《Marine environmental research》2011,71(4):304-311

Benthic diatoms represent an important element of global nutritional productivity; to raise attention on their role, which is often neglected due to analytical difficulties, surface (1 cm top layer) coastal sediments from Gerlache inlet to Penguin Bay at Terra Nova Bay were collected and stored at -20 °C. DNA amplification by real-time PCR, based on diatom-specific oligonucleotide primers designed on small-subunit rRNA (SSU rRNA), was performed in addition to diatom conventional cell counting and spectrophotometric determination of photo-pigments. Moreover, cations and anions were determined in sediments with the aim to identify factors involved in the control of diatom abundance. Diatom distribution was found quite heterogeneous displaying significant differences from site to site. The salinity in sediments ranged from 45.1 at Gerlache inlet to 76.2 at Penguin Bay and it was correlated with cell abundance, biodiversity, amount of pigments and amplified DNA. The dominant species, Fragilariopsis curta, was associated to sediment salinity brines.  相似文献   

Geotechnical characterization of a landslide in a Blue Clay slope   总被引：1，自引：1，他引：0  

Caterina Di Maio  Roberto Vassallo 《Landslides》2011,8(1):17-32

This paper describes the results of an experimental, as well as theoretical, analysis of a landslide in a clay slope at the margin of a small town of Southern Italy, whose reactivation of 1998 caused severe damages to some structures. To protect the upslope urban area, an anchored diaphragm wall and a drainage system were constructed in 2001. In the meantime, in order to understand the processes which caused the reactivation, a Department of the Basilicata Administrative Region provided financial support to a geotechnical investigation. Laboratory tests on undisturbed and reconstituted specimens, in situ pore pressure and deep displacement measurements were carried out. Both experimental and theoretical in situ water content (and porosity) profiles were determined. Theoretical analyses of pore pressure distribution and stability analyses were carried out. The influence of the drainage system on the slope safety factor was evaluated. Experimental and theoretical data suggest that a first time process occurred in the lower part of the landslide system. The upper part moved on pre-existing surfaces on which an average shear strength close to the residual strength was available. Noticeable water content increase was found around some of these surfaces. Erosion at the toe of the landslide was the probable cause of reactivation. The analysis of the drain system effectiveness suggests that drainage has not significantly influenced pore pressures on the considered slip surfaces yet, mainly because of the very low permeability of the clay.  相似文献   

Environmental assessment of water from a uranium mine (Caldas,Minas Gerais State,Brazil) in a decommissioning operation   总被引：1，自引：1，他引：0  

Michelle Burato Campos  Heliana de Azevedo  Marcos Roberto Lopes Nascimento  Cláudio Vítor Roque  Suzelei Rodgher 《Environmental Earth Sciences》2011,62(4):857-863

  相似文献   

Hypogeal geological survey in the “Grotta del Re Tiberio” natural cave (Apennines, Italy): a valid tool for reconstructing the structural setting     

Alice Ghiselli  Marzio Merazzi  Andrea Strini  Roberto Margutti  Michele Mercuriali 《Central European Journal of Geosciences》2011,3(2):155-168

As karst systems are natural windows to the underground, speleology, combined with geological surveys, can be useful tools for helping understand the geological evolution of karst areas. In order to enhance the reconstruction of the structural setting in a gypsum karst area (Vena del Gesso, Romagna Apennines), a detailed analysis has been carried out on hypogeal data. Structural features (faults, fractures, tectonic foliations, bedding) have been mapped in the ”Grotta del Re Tiberio” cave, in the nearby gypsum quarry tunnels and open pit benches. Five fracture systems and six fault systems have been identified. The fault systems have been further analyzed through stereographic projections and geometric-kinematic evaluations in order to reconstruct the relative chronology of these structures. This analysis led to the detection of two deformation phases. The results permitted linking of the hypogeal data with the surface data both at a local and regional scale. At the local scale, fracture data collected in the underground have been compared with previous authors’ surface data coming from the quarry area. The two data sets show a very good correspondence, as every underground fracture system matches with one of the surface fracture system. Moreover, in the cave, a larger number of fractures belonging to each system could be mapped. At the regional scale, the two deformation phases detected can be integrated in the structural setting of the study area, thereby enhancing the tectonic interpretation of the area (e.g., structures belonging to a new deformation phase, not reported before, have been identified underground). The structural detailed hypogeal survey has, thus, provided very useful data, both by integrating the existing information and revealing new data not detected at the surface. In particular, some small structures (e.g., displacement markers and short fractures) are better preserved in the hypogeal environment than on the surface where the outcropping gypsum is more exposed to dissolution and recrystallization. The hypogeal geological survey, therefore, can be considered a powerful tool for integrating the surface and log data in order to enhance the reconstruction of the deformational history and to get a three-dimensional model of the bedrock in karst areas.  相似文献