ALBERT

Description: L’importanza di un terremoto non dipende solo dalla sua intensità epicentrale. Quello del 26 maggio 1798 (Io VII MCS secondo CPTI04) non si può dire una catastrofe ma è di certo un evento «strategico». Si tratta, infatti, del massimo terremoto storico conosciuto per Siena, che è una delle maggiori attrazioni turistiche e quindi uno dei luoghi più frequentati di questo paese. Nell’ultimo ventennio il terremoto del 1798 è stato più volte studiato, sia da sismologi storici nell’ambito delle attività di revisione del catalogo PFG promosse dal GNDT e dall’ING/INGV (Castelli e Camassi, 1995; Castelli et al., 1996; Boschi et al., 1997; Boschi et al., 2000), sia da storici dell’architettura (Gennari, 2005). Siamo ancora lontani dall’aver completamente esplorato la copiosissima documentazione storica potenzialmente utile per una ricostruzione degli effetti di questo terremoto nel centro urbano senese. Tuttavia il campione reso disponibile dagli studi fatti finora è abbastanza significativo da rendere possibile l’avvio di un progetto di microzonazione del centro storico senese e di una serie di indagini miranti a comprendere cosa realmente successe a Siena il 26 maggio 1798 e, per conseguenza, quali effetti ci si possa attendere in occasione di un futuro terremoto di analoga portata. Il centro storico senese ha infatti conservato, almeno nelle grandi linee, una fisionomia molto simile a quella che aveva del 1798 e questa circostanza offre l’opportunità di attualizzare l’esperienza del terremoto del 1798 contribuendo alla identificazione delle eventuali criticità attese in caso di terremoti futuri. Si è perciò creato un gruppo di studio interdisciplinare (geofisica, architettura, sismologia storica, ingegneria sismica, geologia, ecc.) che ha cominciato a predisporre gli elementi necessari per questa ricostruzione. La base di dati storici di cui si dispone comprende descrizioni di danno più o meno dettagliate per circa seicento edifici senesi, su un migliaio da cui era composto il centro urbano nel 1798. Questo campione comprende sia edifici monumentali o comunque di vaste proporzioni (palazzi gentilizi e case di abitazione multipla, chiese, conventi, opifici) sia edifici non monumentali. Il nostro primo scopo è una ricostruzione dettagliata della distribuzione del danno del terremoto del 1798 nell’area urbana. Utilizzando cartografia storica pressoché coeva al terremoto (cfr. Gennari, 2005) e grazie all’impiego di un GIS, è stato possibile trasporre le informazioni storiche sottoforma di carte tematiche (Danno, Vulnerabilità, Interventi richiesti, eccetera). Le Figg. 1 e 2 presentano due esempi di tematismi derivati da dati archivistici. In parallelo a questa analisi verrà svolta una indagine a campione su una ventina di edifici rappresentativi per i quali si eseguiranno stime di comportamento dinamico con la tecnica del tremore sismico ambientale. A completamento della caratterizzazione della risposta sismica dei terreni nell’area del centro storico saranno svolte analisi geologiche e sismiche per definire le aree in cui l’assetto del sottosuolo rende ipotizzabili fenomeni di amplificazione del moto sismico del suolo. Tutti i risultati verranno raccolti in una base dati comune e implementati nel GIS (Figura 2) L’analisi congiunta dei dati di danno (opportunamente interpretati in termini di risposta sismica locale utilizzando il metodo proposto da Goretti e Dolce, 2004; Goretti, 2006) e delle analisi geofisiche e geologiche permetterà di individuare quelle parti del patrimonio edilizio storico più esposte a danno in caso di futuri eventi sismici.

Description: Published

Description: Roma

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: open

Description: The ATIC balloon-born experiment measures the energy spectra of elements from H to Fe in primary cosmic rays from about 100 GeV to 100 TeV. ATIC is comprised of a fully active bismuth germinate calorimeter, a carbon target with embedded scintillator hodoscopes, and a silicon matrix that is used as a main charge detector. The silicon matrix produces good charge resolution for the protons and helium but only a partial resolution for heavier nuclei. In the present paper a charge resolution of ATIC device was improved and backgrounds were reduced in the region from Be to Si by means of the upper layer of the scintillator hodoscope that was used as charge detector together with silicon matrix. Relative fluxes of nuclei B, C, N, O in the energy region from about 20 GeV/nucleon to 200 GeV/nucleon that were obtained from new high-resolution and high-quality charge spectra of nuclei are presented.

Description: The Advanced Thin Ionization Calorimeter (ATIC), a balloon-borne experiment, is designed to investigate the composition and energy spectra of cosmic rays of charge Z = 1 to 26 over the energy range - 10(exp 11) - 10(exp 14) ev. The instrument consists of a silicon matrix charge detector, plastic-scintillator strip hodoscopes interleaved with graphite interaction targets, and an 18 radiation length deep, fully active bismuth germanate (BGO) calorimeter. ATIC has had two successful long duration balloon (LDB) flights launched from McMurdo Station, Antarc't'ica in 2000 and 2002. In this paper, we present the all-particle spectrum extracted from data collected during the ATIC flights, and compare it with results from other experiments at both lower and higher energies.

Description: The highest energy measurements of cosmic ray electrons extend just beyond 1 TeV. High energy electrons are of particular interest because energy losses during interstellar propagation insure that they arrive primarily from nearby sources. This may produce observable structure in their spectrum. Further, it is predicted that electrons and positrons result from the annihilation of many exotic particles deposited as dark matter candidates. These electrons may appear as excesses in the cosmic ray electron spectrum from 200 GeV to 1000 GeV. A new long duration balloon experiment, ECAL, is being planned to provide direct cosmic ray electron measurements from approx.50 GeV to 〉1 TeV. To make these measurements ECAL must discriminate strongly against showers from protons and heavier ions. One of the techniques used to make this discrimination may be based on measuring the secondary neutrons produced by events in the instrument. The neutron detector configuration and technique will be discussed along with its expected performance based on Monte Carlo simulations.

Description: The Advanced Thin Ionization Calorimeter (ATIC) long duration balloon experiment had a successful science flight accumulating 18 days of data (12/02 - 1/03) during a single circumnavigation in Antarctica. ATIC measures the energy spectra of elements from H to Fe in primary cosmic rays using a fully active Bismuth Germanate calorimeter preceded by a carbon target, with embedded scintillator hodoscopes, and a silicon matrix charge detector at the top. Preliminary results from ATIC have been reported in previous conferences. The revised results reported here are derived from a new analysis of the data with improved charge resolution, lower background and revised energy calibration. The raw energy deposit spectra are de-convolved into primary energy spectra and extrapolated to the top of the atmosphere. We compare these revised results to previous data and comment upon the astrophysical interpretation of the results.

Description: Electromagnetic ion cyclotron (EMIC) waves are an important magnetospheric emission, which is excited near the magnetic equator with frequencies below the proton gyro-frequency. The source of bee energy for wave growth is provided by temperature anisotropy of ring current (RC) ions, which develops naturally during inward convection from the plasma sheet These waves strongly affect the dynamic s of resonant RC ions, thermal electrons and ions, and the outer radiation belt relativistic electrons, leading to non-adiabatic particle heating and/or pitch-angle scattering and loss to the atmosphere. The rate of ion and electron scattering/heating is strongly controlled by the Wave power spectral and spatial distributions, but unfortunately, the currently available observational information regarding EMIC wave power spectral density is poor. So combinations of reliable data and theoretical models should be utilized in order to obtain the power spectral density of EMIC waves over the entire magnetosphere throughout the different storm phases. In this study, we present the simulation results, which are based on two coupled RC models that our group has developed. The first model deals with the large-scale magnetosphere-ionosphere electrodynamic coupling, and provides a self-consistent description of RC ions/electrons and the magnetospheric electric field. The second model is based on a coupled system of two kinetic equations, one equation describes the RC ion dynamics and another equation describes the power spectral density evolution of EMIC waves, and self-consistently treats a micro-scale electrodynamic coupling of RC and EMIC waves. So far, these two models have been applied independently. However, the large-scale magnetosphere-ionosphere electrodynamics controls the convective patterns of both the RC ions and plasmasphere altering conditions for EMIC wave-particle interaction. In turn, the wave induced RC precipitation Changes the local field-aligned current distributions and the ionospheric conductances, which are crucial for a large-scale electrodynamics. The initial results from this new self-consistent model of the magnetospheric electric field, RC and EMIC waves will be shown in this presentation.

Description: Earthquake early warning systems (EEWS), based on real-time prediction of ground motion or structural response measures, may play a role in re- ducing vulnerability and/or exposure of buildings and lifelines. Indeed, seismologists have recently developed efficient methods for real-time es- timation of an event’s magnitude and location based on limited informa- tion of the P-waves. Therefore, when an event occurs, estimates of magni- tude and source-to-site distance are available, and the prediction of the structural demand at the site may be performed by Probabilistic Seismic Hazard Analysis (PSHA) and then by Probabilistic Seismic Demand Analysis (PSDA) depending upon EEWS measures. Such an approach contains a higher level of information with respect to traditional seismic risk analysis and may be used for real-time risk management. However, this kind of prediction is performed in very uncertain conditions which may affect the effectiveness of the system and therefore have to be taken into due account. In the present study the performance of the EWWS under development in the Campania region (southern Italy) is assessed by simu- lation. The earthquake localization is formulated in a Voronoi cells ap- proach, while a Bayesian method is used for magnitude estimation. Simu- lation has an empirical basis but requires no recorded signals. Our results, in terms of hazard analysis and false/missed alarm probabilities, lead us to conclude that the PSHA depending upon the EEWS significantly improves seismic risk prediction at the site and is close to what could be produced if magnitude and distance were deterministically known.

Description: Published

Description: 211-232

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: reserved

Description: The city of Palermo (southern Italy) was severely damaged in the past by moderate-magnitude earthquakes located tens of kilometres offshore. The historical monumental heritage and the high density of population motivated large efforts for the seismic risk assessment. We present the geological and seismological studies performed in downtown Palermo as a study case to show how the complexity of an urban environment can be approached with multidisciplinary investigations. Downtown Palermo is characterized by sea deposits in the coastal zone and the alluvial deposits of two rivers (Papireto and Kemonia) of about 150 m width, which were buried and filled during the XVII century. The difficulty of surface geological surveys was compensated through an analysis of aerial photos and more than 2000 borehole data organized in the City-GIS of the Department of Geology and Geodesy of the University of Palermo. A previous study on the well-documented historical damage indicated the major role played by the two river valleys and the sea deposits in controlling the damage distribution, above the assumption of a fairly homogeneous vulnerability of the existing buildings in downtown. To test the feasibility of using ambient noise for recognizing the presence of alluvial deposits in a densely urbanized environment, a large microtremor measurement campaign was performed in Palermo across several profiles. The frequency peaks inferred from the horizontal-to-vertical spectral ratio were compared with numerical simulations to assess the seismic velocity profile and the soil stratigraphy. Moreover, noise data were analyzed through a statistical approach to establish a possible correlation between damage, resonance frequency and amplitude, and geology. After the moderate earthquake of September 6, 2002 (Mw=5.9, 50 km far away), the analysis of the aftershock sequence provided a well documented estimate of the variation of ground motion within the city in the case of linear soil response. Using these aftershocks we computed also synthetic accelerograms of the main shock through Empirical Green’s Functions that provided ground accelerations as large as 50 gals, consistently with the documented EMS-98 intensity. Synthetic accelerograms showed a large variability of horizontal ground motion within the city (a factor of 3 – 4) that confirms the role of local geology in causing an increase of the seismic hazard on sea and alluvial deposits. Finally, we discuss the comparison between the acceleration response spectra calculated for different soil categories and the design elastic spectra provided by EC8.

Description: Unpublished

Description: Lisbon, Portugal

Description: open

Description: The West side of lake of Garda, in Northern Italy, was struck by a ML=5.2 earthquake on November 24, 2004. The felt area is rather large (from Venice to Milan) and the damaged area consists of 66 municipalities, with a number of homeless of about 2200 and estimated direct damages of 215 millions of euros. Most of the damaged structures are old masonry buildings and churches, while there were almost no damage to reinforced concrete structures. The observed distribution of macroseismic intensity shows a strong azimuthal dependence, with high intensity level in a 10x10 km2 area located SW to the epicentre and rather large dispersion of values (ranging from V to VII-VIII) in the first 10 km epicentral distance. Taking into account the vulnerability level of the damaged structures and the features of the geological formations, we tried to explain the observed damage distribution in terms of finite fault properties of the source, despite the moderate magnitude of the event. Thus we hypothesised a fault geometry from seismotectonic considerations and we simulated the event by a high frequency simulation technique (Deterministic Stochastic Method, DSM). The synthetic ground motion parameters were converted into intensity values by empirical relationships and local geological conditions were considered to explain some discrepancies between simulated and observed intensities. It was possible to adequately reproduce both the observed distribution of macroseismic intensity and the ground motion recorded by an accelerometric station located at about 13 km epicentral distance.

Description: Unpublished

Description: Geneva, Switzerland

Description: open

Description: For early-warning applications in particular, the reliability and efficiency of rapid scenario generation strongly depend on the availability of reliable strong ground-motion prediction tools. If shake maps are used to represent patterns of potential damage as a consequence of large earthquakes, attenuation relations are used as a tool for predicting peak ground-motion parameters and intensities. One of the limitations in the use of attenuation relations is that these have only rarely been retrieved from data collected in the same tectonic environment in which the prediction has to be performed. As a consequence, strong ground motion can result in underestimations or overestimations with respect to the recorded data. This also holds for Italy, and in particular for the Southern Apennines, due to limitations in the available databases, both in terms of distances and magnitude. Moreover, for “real-time” early-warning applications, it is important to have attenuation models for which the parameters can be easily upgraded when new data are collected, whether this has to be done during the earthquake rupture occurrence or in the post-event, when all the strong motion waveforms are available. Here we present a strong-motion attenuation relation for early-warning applications in the Campania region (Southern Apennines), Italy. The model has a classical analytical formulation, and its coefficients were retrieved from a synthetic strong-motion database created by using a stochastic approach. The input parameters for the simulation technique were obtained through the spectral analysis of waveforms of earthquakes recorded by the Istituto Nazionale di Geofisica e Vulcanologia (INGV) network for a magnitude range Md (1.5,5.0) in the last fifteen years, and they have been extrapolated to cover a larger range. To validate the inferred relation, comparisons with two existing attenuation relations are presented. The results show that the calibration of the attenuation parameters, i.e., geometric spreading, quality factor Q, static stress drop values along with their uncertainties, are the main concern.

Description: Published

Description: 133-152

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: reserved