1,721,251 research outputs found
Extensive application of seismic microzoning in Italy: methodological approaches and socio-political implications
No full textItalian scientific and technical communities are developing an integrated feasible approach to seismic hazard assessment based on the strict cooperation with local authorities and trained practitioners also operating locally. This approach has a number of implications (technological, pedagogical, and political) and its potential effectiveness (or failure) will also depend on the capability of involved communities (be they small or large) to promote and support preventive actions, taking advantage of the experience acquired in these activities. Without this bottom-up approach involving local communities directly, it will be difficult for our society to cope with future potentially disastrous events
Design earthquake from site-oriented macroseismic hazard estimates
No full textA procedure is presented to determine design earthquakes that are compatible with seismic hazard estimates deduced in terms of macroseismic intensity from a distribution-free, site-oriented approach. Through this procedure it is possible to identify past earthquakes that were mostly responsible for the local hazard, as well as to identify representative magnitude distance pairs to be used for engineering purposes. An example applied to central Italy is discussed and reveals that a design earthquake provided by the approach described here is significantly different from that provided for the same site by the standard disaggregation analysis. This discrepancy is the effect of a different use of information available for hazard assessment at the site under study
Sulla Previsione
Full text linkLa modernità ha delineato il futuro come spazio di libertà. Questo spazio è garantito dalla coesistenza di modelli previsionali legittimati da procedure che ne garantiscono la coerenza interna e sono corroborati da dati osservativi. Ma la coesistenza di modelli potenzialmente efficaci richiede anche una valutazione comparata che attribuisca opportuni valori di verosimiglianza agli scenari alternativi che questi modelli delineano. Sulla base di queste valutazioni, la comunità è chiamata a decidere quali modelli adottare attraverso una pratica politica capace di implementare scelte consapevoli dei vincoli che il paradigma scientifico pone e tenga contestualmente conto dei valori e dei desideri di quella comunità.Modernity has outlined the future as a space of freedom. This space is guaranteed by the coexistence of forecast models legitimized by procedures that guarantee internal consistency and are corroborated by observational data. But the coexistence of potentially effective models also requires a comparative evaluation that attributes appropriate likelihood values to the alternative scenarios that these models outline. Based on these assessments, the community is called upon to decide which models to adopt through a political practice capable of implementing choices that are aware of the constraints that the scientific paradigm poses and jointly consider the values and desires of that community.KeywoRdSForecast, scientific paradigm, models, demonstration and argumentatio
La razionalizzazione della speranza
Full text linkThe rationalization of expectation, here considered as ‘hope’ regarding a possible future, has been declined not with the aim of eliminating uncertainty about the future (which is assumed as an immanent and ineliminable feature of the World) but as aimed at defining a rational behavior in deliberation in conditions of uncertainty. A ‘freely’ rational behavior, in that supported by coherent arguments. This coherency does ensure the success of the action chosen by the deliberating subject, but rather makes this action acceptable by the reference community in the light of its consequences.La razionalizzazione dell’attesa, intesa come aspettativa o ‘speranza’ riguardo ad un futuro possibile, è stata declinata non in funzione dell’eliminazione dell’incertezza sul futuro (che viene assunta come caratteristica immanente ed ineliminabile del mondo) ma come volta a definire il comportamento razionale di un soggetto deliberante a fronte dei possibili esiti delle sue azioni. Un comportamento che viene inteso come ‘liberamente’ razionale, non per le propensioni del soggetto responsabile della deliberazione, quanto piuttosto per la coerenza delle argomentazioni che la supportano. Queste argomentazioni non garantiscono il successo dell’azione scelta dal soggetto deliberante, quanto piuttosto la rendono accettabile da parte della comunità di riferimento alla luce delle sue possibili conseguenze.
The Role of Data Processing and Uncertainty Management in Seismic Hazard Evaluations: Insights from Estimates in the Garfagnana–Lunigiana Area (Northern Italy)
No full textSignificantly different estimates of seismic hazard may result for the same site as an effect of different methodological choices underlying the adopted procedures. In order to explore this aspect, two approaches devoted to probabilistic seismic hazard assessment are considered for the evaluation of hazard in a seismic area in Northern Italy. In particular, results of a standard procedure are compared with those obtained by an innovative approach. Fundamental features of this last methodology are the extensive use of intensity data relative to seismic effects observed at the site of interest during past earthquakes and the basic role attributed to the parameterisation of uncertainty which affects the considered pieces of information. The analysis indicates that the new approach supplies results significantly different from those obtained from standard methodology and that these differences strongly depend on strategies adopted for data processing and for the management of uncertainties which affect input parameters
Attenuation relationship of macroseismic intensity in Italy for probabilistic seismic hazard assessment
No full textA statistical analysis of macrosesmic intensity decay with distance has been conducted by using the most recent compilation of felt intensities relative to Italian earthquakes. An innovative aspect of the present study has been the attempt to define criteria for the validation of the attenuation relationships considered in their complete probabilistic form by a quantitative comparison with observed
macroseismic fields. From the results of our analyses, a new attenuation relationship is proposed for the Italian territory, based on two independent variables only: epicentral intensity and hypocentral distance. Preliminary indications on the existence of differentiated attenuation features of macroseismic intensity over the national territory were gained
Synthetic spectral structure of the seismic ambient vibrations generated by a distribution of superficial random sources with a finite extension
No full textA model of seismic ambient vibrations is presented in the form of a random wavefield generated by a uniform continuous distribution of correlated aleatory forces, located at the surface of a flat layered weakly-dissipative Earth. The frequency-dependent spatial correlation among these sources is assumed to be representative of their spatial extension and has been parametrized by considering the role played by sea-wave dynamics in generating ambient vibrations. This enables a realistic description of the average power spectral density function of ambient vibrations observed worldwide at reference soil conditions. Effectiveness of the model is tested by reproducing observed average Horizontal-to-Vertical Spectral Ratios obtained from ambient vibration measurements at a well documented site in Northern Italy
SASHA: a computer program to assess seismic hazard form intensity data
No full textThe SASHA program for the estimate of seismic hazard from a probabilistic analysis of macroseismic data is presented and made freely available (together with the user guide and sample input files) upon request to the authors. The program allows the computation of typical hazard outputs (hazard curve for different intensity thresholds, intensity or PGA value characterized by a fixed exceedance probability in a given exposure time) for a generic set of sites by fully exploiting information locally available about seismic effects (intensity data) of past earthquakes. This information can be integrated with “virtual” intensity values deduced from epicentral data and macroseismic observations available at neighboring sites. Uncertainties about intensity data and the actual reliability of local seismic histories are taken into account.
SASHA has been developed in the framework of a recent research project devoted to seismic hazard assessment in Italy (INGV-DPC Project S1; http://esse1.mi.ingv.it), where the program has been extensively applied. For this reason, region-dependent coefficients of the empirical relations presently implemented in the code (e.g., to compute intensity attenuation with source distance and to “convert” intensity hazard estimates to PGA) are the ones most recently proposed for the Italian territory. Relevant parameters can, however, be modified by the user to allow application to different countries
Mud volcanoes as natural strainmeters: a working hypothesis
No full textDue to the sub-critical status of the seismogenic crust, relatively small strain fluctuations (> 0.1 mu strain) induced by post-seismic stress redistribution could significantly affect the seismic hazard on a regional scale (tens to thousands of km) in the medium-term (months to tens of years). The physical feasibility of mud volcano monitoring for the detection of crustal strain field fluctuations is discussed. Simple physical arguments are considered to evaluate the response of the mud volcanic system, in terms liquid-outflow or gas discharge variations, to slow pore pressure changes in the reservoir. The application of a new remote sensing technique for large-scale/medium-term monitoring is also suggested
Combining horizontal ambient vibration components for H/V spectral ratio estimates
No full textIn the current literature, several procedures for computing average horizontal to vertical (H/V) spectral ratio of ambient vibrations are interchangeably adopted, whose possible equivalence has never been checked. To this purpose, expected sampling properties of average H/V spectral ratio relative to commonly adopted procedures are determined in the frame of a coherent physical–statistical model. This analysis reveals that all the considered estimators provide H/V estimates that are biased of amounts ranging from 46 per cent up to above 100 per cent of the true value. The amount of these biases is not reduced when H/V spectral ratio estimates are determined, as in the common practice, by averaging H/V spectral ratios computed over a number of time-windows extracted from the experimental record. On the other hand, these biases can be drastically reduced in the case that H/V spectral ratio is computed as the squared root of the ratio of horizontal (whatever the north/south–east/wes
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