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The purpose of this paper is to emphasize the consequences of the ordinal and qualitative nature of seismic intensity regarding its recording. The classical way of recording by an integer value implies that on many occasions it can be difficult to associate only one intensity degree to an event. Therefore, we propose to record the intensity in a new way so that the expert is no longer restricted to indicating only one value, but can express his belief that the considered event belongs to any one of the intensity classes in the scale. Following this approach, as an example, we study the completeness of the Sannio-Matese catalogue and show how the degree of completeness changes according to the degree of uncertainty in intensity assessment. 相似文献
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A version of the restricted trigger model is used to analyse the temporal behaviour of some aftershock sequences. The conditional
intensity function of the model is similar to that of the Epidemic Type Aftershock-Sequence (ETAS) model with the restriction
that only the aftershocks of magnitude bigger than or equal to some threshold Mtr can trigger secondary events. For this reason we have named the model Restricted Epidemic Type Aftershock-Sequence (RETAS)
model. Varying the triggering threshold we examine the variants of the RETAS model which range from the Modified Omori Formula
(MOF) to the ETAS model, including such models as limit cases. In this way we have a quite large set of models in which to
seek the model that fits best an aftershock sequence bringing out the specific features of the seismotectonic region struck
by the crisis. We have applied the RETAS model to the analysis of two aftershock sequences: The first is formed by the events
which followed the strong earthquake of M=7.8 which occurred in Kresna, SW Bulgaria, in 1904. The second includes three main shocks and a large swarm of minor shocks
following the quake of 26 September 1997 in the Umbria-Marche region, central Italy. The MOF provides the best fit to the
sequence in Kresna; that leads to the thought that just the stress field changes due to the very strong main shock generate
the whole sequence. On the contrary, the complex behaviour of the seismic sequence in Umbria-Marche appears when we make the
threshold magnitude vary. Setting the cut-off magnitude M0=2.9 the best fit is provided by the ETAS model, while if we raise the threshold magnitude M0=3.6 and set Mtr=5.0, the RETAS model turns out to be the best model. In fact, observing the time distribution of this reduced data set, it
appears more evident that especially the strong secondary events are followed by a cluster of aftershocks. 相似文献
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The purpose of this article is to show how Bayesian belief networks can beused in analysis of the sequence of the earthquakes which have occurred in a region, to study the interaction among the variables characterizing eachevent. These relationships can be represented by means of graphs consistingof vertices and edges; the vertices correspond to random variables, whilethe edges express properties of conditional independence. We have examinedItalian seismicity as reported in two data bases, the NT4.1.1 catalogue and the ZS.4 zonation, and taken into account three variables: the size of thequake, the time elapsed since the previous event, and the time before the subsequent one. Assigning different independence relationships among these variables, first two couples of bivariate models, and then eight trivariatemodels have been defined. After presenting the main elements constituting a Bayesian belief network, we introduce the principal methodological aspects concerning estimation and model comparison. Following a fully Bayesian approach, prior distributions are assigned on both parameters and structuresby combining domain knowledge and available information on homogeneous seismogenic zones. Two case studies are used to illustrate in detail the procedure followed to evaluate the fitting of each model to the data sets andcompare the performance of alternative models. All eighty Italian seismogenic zones have been analysed in the same way; the results obtained are reportedbriefly. We also show how to account for model uncertainty in predicting a quantity of interest, such as the time of the next event. 相似文献
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Statistical Analysis of the Completeness of a Seismic Catalogue 总被引：1，自引：0，他引：1
Among the numerous issues that the study of seismic events presents, theincompleteness of catalogues is certainly one of the most important. It is also one that only the contribution of many and different skills canprovide with a valid solution. In this paper the search for the complete part of a catalogue is expressed in terms of identification of the changepoint in a hierarchical Bayesian model. Stochastic simulation methods, recently presented in the literature, have enabled us to overcome the computational issues that previously made this approach prohibitive. We have applied the method on data, drawn from the Italian NT4.1.1 catalogue,related to some seismogenetic zones of ZS.4 zonation within which we assumespatial incompleteness to be homogeneous. The results obtained are given inthe concluding sections of the paper. 相似文献
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Renata Rotondi Elisa Varini Carla Brambilla 《Bulletin of Earthquake Engineering》2016,14(7):1777-1796
According to the idea now widespread that macroseismic intensity should be expressed in probabilistic terms, a beta-binomial model has been proposed in the literature to estimate the probability of the intensity at site in the Bayesian framework and a clustering procedure has been adopted to define learning sets of macroseismic fields required to assign prior distributions of the model parameters. This article presents the results concerning the learning sets obtained by exploiting the large Italian macroseismic database DBM1I11 (Locati et al. in DBMI11, the 2011 version of the Italian Macroseismic Database, 2011. http://emidius.mi.ingv.it/DBMI11/) and discusses the problems related to their use in probabilistic modelling of the attenuation in seismic regions of the European countries partners of the UPStrat-MAFA project (2012), namely South Iceland, Portugal, SE Spain and Mt Etna volcano area (Italy). Anisotropy and the presence of offshore earthquakes are some of the problems faced. All the work has been carried out in the framework of the Task B of the project. 相似文献
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Renata Rotondi 《Natural Hazards》1999,19(2-3):139-150
Rotondi and Pagliano considered the problem of identifying periods with different seismicity levels as a multiple-changepoint problem: after having estimated the complete part of the historical catalog related to a seismic source zone, inference was made about the number and the location of k 1 changepoints of the occurrence rate in a sequence of n observations from a generalized Poisson process through a stepwise procedure. In this work, we extend such a method estimating the number of changepoints, their location, and other model parameters simultaneously. A fundamental role is played by new computational methods based on the simulation of Markov chains. In particular, we have applied a new version of the reversible jump Metropolis–Hastings algorithm to the data of some Italian seismic sources and we have identified periods with alternately higher and lower seismic activity levels. 相似文献
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F. Meroni G. Zonno R. Azzaro S. D’Amico T. Tuvè C. S. Oliveira M. A. Ferreira F. Mota de Sá C. Brambilla R. Rotondi E. Varini 《Bulletin of Earthquake Engineering》2016,14(7):1979-2008
A procedure for seismic risk assessment is applied to the Mt. Etna area (eastern Sicily, Italy) through assessment of urban system dysfunction following the occurrence of an earthquake. The tool used is based on the Disruption Index as a concept implemented in Simulator QuakeIST, which defines urban disruption following a natural disaster. The first element of the procedure is the definition of the seismic input, which is based on information about historical seismicity and seismogenic faults. The second element is computation of seismic impact on the building stock and infrastructure in the area considered. Information on urban-scale vulnerability was collected and a geographic information system was used to organise the data relating to buildings and network systems (e.g., building stock, schools, strategic structures, lifelines). The central idea underlying the definition of the Disruption Index is identification and evaluation of the impact on a target community through the physical elements that most contribute to severe disruption. The procedure applied in this study (i.e., software and data) constitutes a very useful operational tool to drive the development of strategies to minimise risks from earthquakes. 相似文献
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We consider point processes defined on the space–time domain which model physical processes characterized qualitatively by the gradual increase over time in some energy until a threshold is reached, after which, an event causing the loss of energy occurs. The risk function will, therefore, increase piecewise with sudden drops in correspondence to each event. This kind of behaviour is described by Reid's theory of elastic rebound in the earthquake generating process where the quantity that is accumulated is the strain energy or stress due to the relative movement of tectonic plates. The complexity and the intrinsic randomness of the phenomenon call for probabilistic models; in particular the stochastic translation of Reid's theory is given by stress release models. In this article we use such models to assess the time-dependent seismic hazard of the seismogenic zone of the Corinthos Gulf. For each event we consider the occurrence time and the magnitude, which is modelled by a probability distribution depending on the stress level present in the region at any instant. Hence we are dealing here with a marked point process. We perform the Bayesian analysis of this model by applying the stochastic simulation methods based on the generation of Markov chains, the so called Markov chain Monte Carlo (MCMC) methods, which allow one to reconcile the model's complexity with the computational burden of the inferential procedure. Stress release and Poisson models are compared on the basis of the Bayes factor. 相似文献
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