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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS003 Oral Presentation 1867
Can an Early Warning System in Northern Italy be Useful
Mrs. Paola Traversa
LGIT CNRS - UJF Grenoble - France IAVCEI
Lai Carlo, Strobbia Claudio
The aim of an Earthquake Early Warning System (EEWS) is to provide the community with a pre-alarm
of a few seconds before a potentially damaging ground motion strikes sensible objectives. In order to
make a EEWS effective and useful it is therefore essential to properly assess a) the expected prealarming
times for a given site and seismotectonic context and b) the intensity of ground motion
generated at the site by a possible earthquake scenario. An adequate consideration of these issues is
essential in the implementation of a feasibility study of an EEWS and this is particular relevant in areas
like Northern Italy characterized by low to medium seismicity. At the purpose of assessing the potential
usefulness and reliability of an EEWS in the hospitals of Lombardy Region, we have carried out a series
of numerical simulations of ground motion caused by two realistic earthquake scenarios corresponding
to fault ruptures along potentially active seismogenic structures. In order to validate the results of the
numerical simulations with real records, the earthquake scenarios have been chosen to correspond to
two seismic events recently occurred in Northern Italy. The synthetic seismograms have been calculated
using two computer programs based on an extended kinematic model of the source which fully solve
the inhomogeneous elastodynamic problem. The results of numerical simulations were compared in the
time domain with real recordings showing very good agreement in terms of amplitudes of ground
motion and its spatial decay. The synthetic seismograms also allowed to estimate the temporal
separation or phase delay between the first arrivals of P and S phases at given locations as a function of
distance from the seismic source. This is the basis for estimating the pre-alarm times that can be used
to automatically shut-down the functioning of sensitive equipments and prevent catastrophic chain
failures. Using a simple geometrical model, a sensitivity study was carried out to assess the influence of
relevant seismological parameters used in the numerical simulations. This study revealed a rather strong
correlation between the time separation of P and S first arrivals and the thickness of the layers of the
crustal model adopted in the analyses. More specifically the travel times-distances curves turned out to
be mainly affected by the characteristics of the two thickest layers of the crustal model. Finally a
preliminary investigation has been made with regard to the influence of possible site amplification
effects which may alter the intensity of simulated ground motion calculated for the standard stiff ground
(outcropping rock) conditions.
Keywords: early warning, italy, simulation