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991.
Variations of local seismic response in Benevento (Southern Italy) using earthquakes and ambient noise recordings 总被引:1,自引:0,他引:1
Luigi?ImprotaEmail author Giuseppe?Di?Giulio Antonio?Rovelli 《Journal of Seismology》2005,9(2):191-210
The city of Benevento (Southern Italy) has been repeatedly struck by large historical earthquakes. A heterogeneous geologic structure and widespread soft soil conditions make the estimation of site effects crucial for the seismic hazard assessment of the city. From 2000 until 2004, we installed seismic stations to collect earthquake data over zones with different geological conditions. Despite the high level of urban noise, we recorded more than 150 earthquakes at twelve sites. This data set yields the first, well documented experimental evidence for weak to moderate local amplifications. We investigated site effects primarily by the classical spectral ratio technique (CSR) using a rock station placed on the Benevento hill as reference. All sites in the Calore river valley and in the eastern part of the Benevento hill show a moderate high-frequency (f > 4 Hz) amplification peak. Conversely, sites in the Sabato river valley share weak-to-moderate amplification in a wide frequency band (from 1–2 to 7–10 Hz), without evident frequency peaks. Application of no-reference-site techniques to earthquake and noise data confirms the results of the CSRs in the sites of the Calore river valley and of the eastern part of the Benevento hill, but fails in providing indications for site effects in the Sabato river valley, being the H/V ratios nearly flat. One-dimensional modeling indicates that the ground motion amplification can be essentially explained in terms of a vertically varying geologic structure. High-frequency narrow peaks are caused by the strong impedance contrast existing between near-surface soft deposits and stiff cemented conglomerates. Conversely, broad-band amplifications in the Sabato river valley are likely due to a more complex layering with weak impedance contrasts both in the shallow and deep structure of the valley. 相似文献
992.
Phosphorus dynamics in water and sediments in urbanized and non-urbanized rivers in Southern Brazil 总被引:1,自引:0,他引:1
Pagliosa PR Fonseca A Bosquilha GE Braga ES Barbosa FA 《Marine pollution bulletin》2005,50(9):965-974
Phosphorus flux models show that the removal tends to be a common feature in polluted estuarine systems whereas the release of P to the adjacent coastal area occurs in pristine environments. This study analyzes the distribution of P in water and sediments along six rivers in the south coast of Brazil. Three rivers located inside protected areas were considered non-polluted and used as a control of urbanization. The other three, situated within urbanized areas, were considered as having highly elevated concentrations of P. Results showed a different behavior of P in water and sediments located in urbanized and non-urbanized areas. The concentrations of dissolved organic (P-org) and inorganic (P-inorg) phosphorus in water, and the total phosphorus (P-tot) and polyphosphate (P-poly) in sediments where higher in the urbanized rivers compared to the non-urbanized ones. Both P of punctual origin and of diffuse origin contributed to the maintenance of elevated concentrations and disturbed the natural fluxes along the polluted rivers. The minimum and maximum concentrations in urbanized areas varied from 0.39 to 12.45 (microM) for P-org and 0.00 to 5.92 (microM) for P-inorg in water, and in sediments from 89.90 to 808.16 (microM g(-1)) for P-tot and 0.00 to 76.51 (microM g(-1)) for P-poly. In non-urbanized areas concentrations in water varied from 0.22 to 1.20 (microM) for P-inorg and 4.43 to 5.56 (microM) for P-org, and in sediments from 45.91 to 652.26 (microM g(-1)) for P-tot and 0.00 to 8.61 (microM g(-1)) for P-poly. Using a hierarchical sampling design and a simple model of variation of P (K(d) model) it was possible to demonstrate that urbanized and non-urbanized estuaries may act as sinks or sources of P. The variation of P analysis in different points along each of the six rivers showed that release and removal areas may occur within a same river independently of its urbanization. 相似文献
993.
Gerardo?SeverinoEmail author Vladimir?Cvetkovic Antonio?Coppola 《Computational Geosciences》2005,9(4):155-177
We consider groundwater steady flow in a heterogeneous porous formation of random and stationary log-conductivity Y = ln K, characterized by the mean 〈Y〉, and the two point correlation function C
Y
which in turn has finite, and different horizontal and vertical integral scales I and I
v
, respectively. The fluid velocity V, driven by a given head drop applied at the boundary, has constant mean value U ≡ (U, 0, 0). Approximate explicit analytical expressions for transverse velocity covariances are derived. The adopted methodology
follows the approach developed by Dagan and Cvetkovic (Spatial moments of kinetically sorbing plume in a heterogeneous aquifers,
Water Resour. Res. 29 (1993) 4053) to obtain a similar result for the longitudinal velocity covariance. Indeed, the approximate
covariances of transverse velocities are determined by requiring that they have the exact first order variances as well as
zero integral scale (G. Dagan, Flow and Transport in Porous Formations (Springer, 1989)) , and provide the exact asymptotic limits of the displacement covariance of the fluid particles obtained
by Russo (On the velocity covariance and transport modeling in heterogeneous anisotropic porous formations 1. Saturated flow,
Water Resour. Res., 31 (1995) 129). Comparisons with numerical results show that the proposed expressions compare quite well in the early time
regime, and for Ut/I >100. Since most of the applications, like assessing the effective mobility of contaminants or quantifying the potential
hazards of nuclear repositories, require predictions over higher times the proposed approximate expressions provide acceptable
results. The main advantage related to such expressions is that they allow obtaining closed analytical forms of spatial moments
pertaining to kinetically sorbing contaminant plumes avoiding the very heavy computational effort which is generally demanded.
For illustration purposes, we consider the movement of one contaminant species, and show how our approximate spatial moments
compare with the numerical simulations. 相似文献
994.
Traditionally, urban analysis has been quick to adopt and benefit from developments in technology (e.g., microcomputer, GIS) and techniques (e.g., statistics, mathematical programming). This has not been the case, however, with newer methods of spatial analysis — in particular, spatial statistics. Only recently has this situation started to change. This paper documents the confluence of spatial statistics and urban analysis by first reviewing developments in spatial statistics, and then presenting examples of recent applications in urban analysis. The developments reviewed fall under the rubric of global and local forms of spatial analysis, and cover three major technical issues: spatial association, spatial heterogeneity and the modifiable areal unit problem. The examples highlight the relevance and usefulness of the techniques reviewed for urban transportation and land-use applications. The paper concludes with conjectures concerning future developments at the intersection of spatial statistics and urban analysis. 相似文献
995.
The consistent tangent matrix for density‐dependent plastic models within the theory of isotropic multiplicative hyperelastoplasticity is presented here. Plastic equations expressed as general functions of the Kirchhoff stresses and density are considered. They include the Cauchy‐based plastic models as a particular case. The standard exponential return‐mapping algorithm is applied, with the density playing the role of a fixed parameter during the nonlinear plastic corrector problem. The consistent tangent matrix has the same structure as in the usual density‐independent plastic models. A simple additional term takes into account the influence of the density on the plastic corrector problem. Quadratic convergence results are shown for several representative examples involving geomaterial and powder constitutive models. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
996.
A detailed field study of 39 centimetre- to metre-scale relay ramps from two outcrops was performed to investigate the development of a linkage criterion for segmented normal faults. We analysed the displacement distribution and the geometry of fault arrays containing three types of relay ramp: open, linked, and fully breached, in order to identify which parameters are relevant to fault linkage, and to establish a linkage criterion. Each relay ramp geometry has a specific graphical field on a relay displacement–separation diagram. The field including all the linked geometries (initiation of linkage) separates open and fully breached relay ramps and is interpreted as a value of relay displacement to separation ratio for which faults link during their overlap. A ‘linkage threshold’, in each studied fault system, is defined as the best-fit linear trend of linked relays. We discuss the scaling and the variability of the linkage criterion using published datasets from a wide variety of settings and scales. The observed linkage threshold is linear, with a slope value varying less than one order of magnitude. This suggests that linking relay ramps have self-similar geometries from centimetre- to kilometre-scale and that normal fault linkage is governed by similar fault interaction across a broad range of scales. The linkage criterion, which can be an effective tool to estimate relay ramp geometry at depth or at the earth surface, could therefore be used to improve investigations in determining fluid entrapment or in the evaluation of potential surface of seismic ruptures. 相似文献
997.
Veridiana T. de S. Martins Wilson Teixeira Carlos M. Noce Antonio C. Pedrosa-Soares 《Gondwana Research》2004,7(1):75-89
Nd and Sr isotope data were obtained for three plutonic suites (595–505 Ma) and distinct young granitoid intrusions (503 Ma), from the southern part of the Neoproterozoic Araçuaí Orogen. The Sr and Nd isotopes (87Sr/86Sr, eNd) and TDM values from the plutons and distinct basement rocks are used to constrain the magma genesis of the granitoid plutons. These isotopic parameters, with eNd values ranging from −4 to −24 and TDM ages from 1.3 to 2.8 Ga, for the granitoid suites, and −5 to −40 and 3.5 to 1.5 Ga, for the distinct Archean and Proterozoic basement complexes, suggest that the Jequitinhonha Complex metasediments are the main crustal source for most of these plutons, except for the youngest granitoid intrusions, which may have a protolith similar to the Mantiqueira and Guanhães complexes. Furthermore, the isotope data indicate a minor, but important, participation of Neoproterozoic oceanic lithosphere in the granite genesis, which corroborates with a confined orogenic model and a narrow oceanic consumption (B-subduction) for the Araçuaí Orogen. 相似文献
998.
Traditionally, urban analysis has been quick to adopt and benefit from developments in technology (e.g., microcomputer, GIS) and techniques (e.g., statistics, mathematical programming). This has not been the case, however, with newer methods of spatial analysis — in particular, spatial statistics. Only recently has this situation started to change. This paper documents the confluence of spatial statistics and urban analysis by first reviewing developments in spatial statistics, and then presenting examples of recent applications in urban analysis. The developments reviewed fall under the rubric of global and local forms of spatial analysis, and cover three major technical issues: spatial association, spatial heterogeneity and the modifiable areal unit problem. The examples highlight the relevance and usefulness of the techniques reviewed for urban transportation and land-use applications. The paper concludes with conjectures concerning future developments at the intersection of spatial statistics and urban analysis. 相似文献
999.
Antonio Tadeu dos Reis Christian Gorini Alain Mauffret Michelle Mepen 《Comptes Rendus Geoscience》2004,336(2):125-133
The Pyreneo-Languedocian submarine sediment body, located in the western sector of the Gulf of Lions, is an example of a fan-like depositional system essentially controlled by salt tectonics. The area was subjected to a combined effect of overburden subsidence into the evacuated salt layer and a significant distal salt thickening, due to preferential basinward salt migration. This mode of salt migration impacted the Quaternary sea-bottom morphology by creating a large midslope topographic low, providing space accommodation for the Pyreneo-Languedocian fan. At gulf scale, the fan is a unique feature because unchannelized sedimentary environment in the area occurs at slope level, thus in minor water depth in relation to all other deep-water sedimentary systems offshore Gulf of Lions. To cite this article: A.T. dos Reis et al., C. R. Geoscience 336 (2004). 相似文献
1000.
Andrea Di Giulio Barbara Carrapa Roberto Fantoni Luciano Gorla Antonio Valdisturlo 《International Journal of Earth Sciences》2001,90(3):534-548
The main steps of the sedimentary evolution of the west Lombardian South Alpine foredeep between the Eocene and the Early Miocene are described. The oldest is a Bartonian carbonate decrease in hemipelagic sediments linked with an increase in terrigenous input, possibly related to a rainfall increase in the Alps. Between the Middle Eocene and the early Chattian, a volcanoclastic input is associated with an extensional tectonic regime, coeval with magma emplacement in the southern-central Alps, and with volcanogenic deposits of the European foredeep and Apennines, suggesting a regional extensional tectonic phase leading to the ascent of magma. During Late Eocene to Early Oligocene, two periods of coarse clastic sedimentation occurred, probably controlled by eustasy. The first, during Late Eocene, fed by a local South Alpine source, the second, earliest Oligocene in age, supplied by the Central Alps. In the Chattian, a strong increase in coarse supply records the massive erosion of Central Alps, coupled with a structures growth phase in the subsurface; it was followed by an Aquitanian rearrangement of the Alpine drainage systems suggested by both petrography of clastic sediments and retreat of depositional systems, while subsurface sheet-like geometry of Aquitanian turbidites marks a strong decrease in tectonic activity. 相似文献