[Forum SIS] avviso seminario R. Rotondi 12/6 Venezia

[romanaz a unive.it]

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AVVISO DI SEMINARIO
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Martedi' 12 GIUGNO 2012 alle ore 10, nell'aula E del plesso di Santa
Marta, Dipartimento di Scienze Ambientali, Informatica e
Statistica, Universita' Ca' Foscari, Venezia

*Renata Rotondi*
Senior Researcher
Istituto di Matematica Applicata e Tecnologie Informatiche, CNR, Milano

terra' un seminario dal titolo:

*Bayesian inference in seismic risk analysis:
nonparametric estimation of earthquake recurrence time density*

Abstract:
The knowledge of a physical model able to explain in its entirety the
generation of earthquakes at the various time-space scales involved in the
process is still, and will be for long time, a challenging goal.
Consequently, the stochastic model development is grounded on the
combination of widely shared physical hypotheses and powerful statistical
tools. Among the formers there is the idea that the time elapsed since the
last strong shock affects the occurrence of a future event, that is, that
after a large earthquake the stress accumulation process restarts so as
the times between consecutive large seismic events can be considered as
realizations of independent, identically distributed random variables.

Various probability distributions F have been proposed for the intervent
times in the literature but the results are not completely satisfactory,
also because the data, generally sparse and irregular, are difficult to
fit through parametric models. The proposed solution consists in assuming
that F is a random distribution modelled by a mixture of Polya tree
processes which, under mild assumptions, assigns probability one to the
space of the continuous distributions. The estimation technique is based
on a MCMC sampler using Metropolis-Hastings within Gibbs sampling and on
data simulation.

The  model is applied to the Italian earthquakes with (moment) magnitude
greater han 5.3 drawn from the CPTI04 catalogue and having epicenter into
the seismogenic areas of the database DISS, subdivided into eight
tectonically-coherent macro-regions.

Retrospective validation on the events recorded in some decades of the
past century is used: (1) to test the model; (2) to support changes of the
geological database, (3) to inspire guidelines of a national protocol for
the operational use of long-term forecasts by Civil Protection.