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311.
The study computes time-dependant earthquake probabilities on the basis of seismicity data mainly deriving from historic records.
It provides a methodological approach useful for those countries where the scarcity of instrumental data and/or paleoseismological
evidences requires that historical information shall be stressed. Thus, the conditional probability that damaging earthquakes
(M ≥ 6) may occur in Italy in the next 30 years is shown, and the potential for the main worldwide known Italian cities with
a cultural heritage is outlined. Earthquake probabilities are computed referring to the application of renewal processes,
where the periodicity is analytically modelled by means of the Brownian Passage Time function; an estimate of the dispersion
(i.e., uncertainty) introduced on probabilities is provided making use of Monte Carlo simulations. The computed probabilities
refer to seismic source zones deriving from the spatial clustering of the historically documented seismicity. The computation
of probabilities based on the interaction of earthquakes occurring in nearby zones, has been also attempted for a test area
to explore the influence exerted by the stress transfer effect. The main findings of this study are that (1) seismic source
zones in Southern Italy are the most prone to experience damaging earthquakes in the next 30-years, with conditional probabilities
a large as 10%; and (2) the influence exerted by the earthquake interaction in increasing such probabilities, doesn’t seem
to be relevant, because the mean recurrence times of large earthquakes (above the threshold magnitude of six chosen in this
study) are in general much longer than the time shortening produced by the stress transfer. 相似文献
312.
We investigate the properties of intermittency of magnetic turbulence by using magnetic field data collected by the Helios spacecraft in the inner heliosphere. Clear scaling laws for magnetic structure functions are visible in periods where the velocity of the bulk plasma is low. Within these periods we found that intermittency of magnetic turbulence is high with respect to velocity field. A comparison with fluid flows where passive scalars are more intermittent than velocity, yields to consider the magnetic field like a “passive vector”. 相似文献
313.
Will J. Percival Carlton M. Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Matthew Colless Chris Collins Warrick Couch Gavin Dalton Roberto De Propris Simon P. Driver George Efstathiou Richard S. Ellis Carlos S. Frenk Karl Glazebrook Carole Jackson Ofer Lahav Ian Lewis Stuart Lumsden Steve Maddox Stephen Moody Peder Norberg John A. Peacock Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2001,327(4):1297-1306
The 2dF Galaxy Redshift Survey has now measured in excess of 160 000 galaxy redshifts. This paper presents the power spectrum of the galaxy distribution, calculated using a direct Fourier transform based technique. We argue that, within the k -space region , the shape of this spectrum should be close to that of the linear density perturbations convolved with the window function of the survey. This window function and its convolving effect on the power spectrum estimate are analysed in detail. By convolving model spectra, we are able to fit the power-spectrum data and provide a measure of the matter content of the Universe. Our results show that models containing baryon oscillations are mildly preferred over featureless power spectra. Analysis of the data yields 68 per cent confidence limits on the total matter density times the Hubble parameter , and the baryon fraction , assuming scale-invariant primordial fluctuations. 相似文献
314.
315.
Two conceptually different procedures to obtain upper bounds to displacements and deformations developed in the dynamic evolution of elasto-plastic structures are considered. Computationally, both methods require the dynamic analysis of a linear system and a sequence of constrained optimization problems, each roughly analogous to a limit analysis procedure in the quasi-static range, with a substantial saving in effort when compared to an incremental analysis of the plasto-dynamic response. A discrete model for frames is proposed and the two approaches are reformulated in a convenient matrix form. The approaches are then compared on the basis of the information needed (total or plastic displacements, deformations, dissipated energy), of the usefulness of results obtained and of the computational effort involved. The results seem to indicate the practical usefulness of these techniques and encourage the extension of the study to broader classes of structures. 相似文献
316.
317.
A first generation of probabilistic seismic hazard maps of the Italian country are presented. They are based on seismogenic zoning deriving from a kinematic model of the structural tectonic units and on an earthquake catalogue with the foreshock and aftershock events filtered out. The following ground motion parameters have been investigated and mapped using attenuation equations based on strong-motion recordings of Italian earthquakes: peak ground acceleration and velocity; Arias intensity; strong motion duration; and the pseudovelocity and pseudoacceleration spectral values at 14 fixed frequencies both for the vertical and the largest horizontal component. A Poissonian model of earthquake occurrence is assumed as a default and the hazard maps are presented in terms of ground motion values expected to be exceeded at a 10% probability level in 50 years (return period 475 years) according to the requirement of Eurocode 8 for the seismic classification of national territories, as well as in terms of exceedance probabilities of selected ground motion values. Finally, as a tentative study, the use of hybrid methods (implementing both seismogenic zones and structures), renewal processes (including earthquake forecasting) and the influence of site effects (as the basis for the planning of earthquake scenarios) were explored. 相似文献
318.
319.
Roberto De Propris 《Monthly notices of the Royal Astronomical Society》2000,316(1):L9-L12
We calculate the contribution to Balmer line indices from far ultraviolet component sources. We find that this is significant, and may lead to identification of spurious age differences of the order of a total span of ∼6 Gyr or ∼15 per cent size bursts observed a few Gyr after star formation stops. We suggest that claims for intermediate-age populations in early-type galaxies may need to be reconsidered in the light of this new evidence. 相似文献
320.
Roberto Danovaro Norberto Della Croce Antonio Dell'Anno Mauro Fabiano Daniela Marrale Daniela Martorano 《Progress in Oceanography》2000,46(2-4)
Downward fluxes of labile organic matter (lipids, proteins and carbohydrates) at 200 (trap A) and 1515 m depth (trap B), measured during a 12 months sediment trap experiment, are presented, together with estimates of the bacterial and cyanobacterial biomasses associated to the particles. The biochemical composition of the settling particles was determined in order to provide qualitative and quantitative information on the flux of readily available organic carbon supplying the deep-sea benthic communities of the Cretan Sea. Total mass flux and labile carbon fluxes were characterised by a clear seasonality. Higher labile organic fluxes were reported in trap B, indicating the presence of resuspended particles coming from lateral inputs. Particulate carbohydrates were the major component of the flux of labile compounds (on annual average about 66% of the total labile organic flux) followed by lipids (20%) and proteins (13%). The biopolymeric carbon flux was very low (on annual average 0.9 and 1.2 gC m−2 y−1, at trap A and B). Labile carbon accounted for most of the OC flux (on annual average 84% and 74% in trap A and B respectively). In trap A, highest carbohydrate and protein fluxes in April and September, corresponded to high faecal pellet fluxes. The qualitative composition of the organic fluxes indicated a strong protein depletion in trap B and a decrease of the bioavailability of the settling particles as a result of a higher degree of dilution with inorganic material. Quantity and quality of the food supply to the benthos displayed different temporal patterns. Bacterial biomass in the sediment traps (on average 122 and 229 μgC m−2 d−1 in trap A and B, respectively) was significantly correlated to the flux of labile organic carbon, and particularly to the protein and carbohydrate fluxes. Cyanobacterial flux (on average, 1.1 and 0.4 μgC m−2 d−1, in trap A and B, respectively) was significantly correlated with total mass and protein fluxes only in trap A. Bacterial carbon flux, equivalent to 84.2 and 156 mgC m−2 y−1, accounted for 5–6.5% of the labile carbon flux (in trap A and B respectively) and for 22–41% protein pool of the settling particles. These results suggest that in the Cretan Sea, bacteria attached to the settling particles represent a potential food source of primary importance for deep-sea benthic communities. 相似文献