Search

Il terremoto del 20 maggio 2012, in Emilia, ha evidenziato un problema comune nelle mappe di pericolosità sismica definite secondo il classico approccio probabilistico (probabilistic seismic hazard assessment, PSHA). L’evento si è verificato in un’area classificata a “bassa pericolosità sismica” nella attuale mappa nazionale, pubblicata nel 2004 (Gruppo di Lavoro, Redazione della mappa di pericolosità sismica, rapporto conclusivo, 2004, http://zonesismiche.mi.ingv.it/mappa_ps_apr04/italia.html). L’ultima revisione della classificazione sismica era stata motivata dal terremoto di S. Giuliano di Puglia (31 ottobre 2002), avvenuto anch’esso in un’area precedentemente definita a bassa pericolosità sismica. La precedente classificazione era stata aggiornata nel 1981-1984, dopo che le precedenti mappe avevano mancato il terremoto dell’Irpinia del 1980. Dunque, sebbene le mappe di pericolosità abbiano l’intento di “prevedere” la pericolosità associata ai possibili terremoti futuri, tali mappe hanno dovuto essere sistematicamente aggiornate dopo aver mancato un forte terremoto. Questo equivale a chiudere il recinto dopo che i buoi sono fuggiti. Alla luce dei limiti evidenziati dal terremoto dell’Emilia, cosa ne sarà delle attuali mappe di pericolosità sismica e delle relative norme recentemente entrate in vigore? Prima di procedere a modifiche ed aggiornamenti è essenziale capire che cosa non ha funzionato e soprattutto perchè.

In precedenti articoli 1,2 è stato trattato il problema degli effetti di sito dal punto di vista teorico, ovve- ro sulla base della teoria della propagazione delle perturbazioni ondose. Qui vengono presentate e di- scusse molteplici conferme sperimentali del problema, già definito in modo formale, relativo all’utilizzo dei così detti effetti di sito nella quantificazione della peri- colosità sismica. L’effetto di sito è solitamente associa- to alle condizioni geologiche locali, che aumentano (+) o riducono (-) il livello di scuotimento, rispetto a con- dizioni standard di attenuazione dell’energia sismica.

The mechanism of the disruption, both lithospheric thinning and oceanization of the commonly accepted long-term-stable Archaean craton, is still an open question. The available models, all imply a bottom to top process. With the construc- tion of a 1660-km-long transect across the eastern North China Craton (NCC), we demonstrate that both the P-wave velocity and density in the lowermost crust beneath the central section are significantly higher than in the corresponding parts of the south and north sections on the transect. These features are interpreted as geophysical signature of lower crustal under- plating, which supplies sufficiently high gravitational potential energy to trigger lateral flow of the lower crust. This magma underplating-triggered bilateral lower crust flow may facilitate the lithospheric thinning by means of asthenosphere upwelling and decompression melting, which infill the gap produced by the lower crust flow. The underplating-triggered lower crustal flow can provide an alternative mechanism to explain the NCC lithosphere disruption, which highlights the crustal feedback to Archaean lithosphere disruption, from top to bottom.

The crust and upper mantle structure of the Eastern Mediter- ranean is investigated through the nonlinear inversion of Raleigh wave dispersion curves extracted from broadband records in the region along two profiles crossing the Hellenic and Cyprian arcs. Corresponding density models are con- structed, consistent with the observed gravity anomalies. The modelled profiles exhibit a continental crust type overlain by a thick sedimentary cover and underlain by a thick lithospheric mantle. The lithosphere-asthenosphere system exhibits fea- tures, which suggest the presence of upducted asthenosphere exhumed to the north of the Hellenic arc, where the slab extension is limited to depths of about 220 km.

Following a procedure similar to that developed and applied in the Rhone Valley, France (Gorshkov and Gaudemer, 2012), a preliminary identification of the areas prone to earthquakes with magnitude larger or equal to 5.0 (referred as M5+ hereinafter) has been carried out for the Po plain.

Lessons learnt from the destructive earthquakes occurred during the new millennium provide new opportunities to take action, revise and improve the procedure for seismic hazard assessment. When dealing with cultural heritage and critical structures (e.g. nuclear power plants), where it is necessary to consider extremely long time intervals, the standard hazard estimates are by far unsuitable, due to their basic heuristic limitations. A viable alternative to traditional seismic hazard assessment is represented by the use of the scenario earthquakes, characterized at least in terms of magnitude, distance and faulting style, and by the treatment of complex source processes. The scenario-based methods (NDSHA) for seismic hazard analysis, where realistic and duly validated synthetic time series, accounting for source, propagation and site effects, are used to construct earthquake scenarios. The NDSHA procedure provides strong ground motion parameters based on the seismic waves propagation modeling at different scales accounting for a wide set of possible seismic sources and for the available information about structural models. Actually, the proposed method can be applied at regional (national) scale, computing seismograms at the nodes of a grid with the desired spacing, also integrated with time dependent scenarios, or at local (metropolitan) scale, taking into account detailed source characteristics, the path and local geological and geotechnical conditions by means of 3D laterally heterogeneous anelastic models. The relevance of the realistic modeling, which permits the generalization of empirical observations by means of physically sound theoretical considerations, is evident, as it allows for the optimization of the structural design with respect to the site of interest.

A new analytical methodology for computing synthetic seismograms in 3-D anelastic media is applied to the modelling of the local records of the 2003 Bam Mw 6.6 earthquake, Southeastern Iran. The method is based on the combination of the modal summation technique with the asymptotic ray theory. The 3-D models are determined by a set of vertically heterogeneous sections (1-D structures) that are juxtaposed on a regular grid. The distribution of these sections in the grid is done in such a way to satisfy the condition of applicability of the WKBJ approximation, that is, the lateral variation of all the elastic parameters has to be small with respect to the prevailing wavelength. The procedure, described very briefly, has been applied for the area of the destructive 2003 December 26 Bam earthquake Mw 6.6, with a maximum cut-off frequency of 6 Hz. Synthetic seismograms show fine agreement with recorded signals when comparing shapes, amplitudes and spectra and evidence the relevance of 3-D effects.

Recent advances in the physical knowledge of seismic waves generation and propagation processes, along with the improving computational tools, make it feasible the realistic modeling of the ground shaking caused by an earthquake, taking into due consideration the complexities of the source and of the propagation path. A neo- deterministic scenario based approach to seismic hazard assessment (NDSHA) has been developed that naturally supplies realistic time series of ground shaking, including reliable estimates of ground displacement readily applicable to seismic isolation techniques. The NDSHA procedure permits incorporating, as they become available, new geophysical and geological data, as well as the information from the different pattern recognition techniques developed for the space-time identification of strong earthquakes. All this leads to the natural definition of a set of scenarios of expected ground shaking at the bedrock. At the local scale, further investigations can be performed taking into account the local soil conditions, in order to compute the seismic input (realistic synthetic seismograms) for engineering analysis of relevant structures, such as historical and strategic buildings. The NDSHA approach has been already applied in several regions worldwide, including a number of local scale studies accounting for two-dimensional and three-dimensional lateral heterogeneities in inelastic media. A pilot application of the approach, including the detailed evaluation of the expected ground motion accounting for site effects and seismic engineering analysis, has been carried out at a site located in the Friuli Venezia Giulia Region (NE Italy). Further some applications worldwide of a new, highly efficient analytical methodology, developed for modeling the propagation of the seismic wavefield in three-dimensional inelastic media, are presented. This procedure, based on computer codes developed from a detailed knowledge of the seismic source process and the propagation of seismic waves in heterogeneous media, allows not only the detailed study of instrumental and macroseismic data but also the realistic estimate of the seismic hazard, in those areas for which scarce (or no) historical or instrumental information is available, and the relevant parametric analyses: different source and structural models can be taken into account to create a wide range of possible groundshaking scenarios from which to extract essential information, including uncertainty ranges, for decision making.

Una valutazione attendibile dello scuotimento del suolo, eventualmente comprendente indicazioni temporali, è essenziale per pianificare azioni efficaci di mitigazione del rischio sismico. La capacità di anticipare lo scuotimento associato ai terremoti futuri, in ogni caso, deve essere provata mediante un rigoroso processo di validazione. Il terremoto del 20 maggio 2012, in Emilia, ha evidenziato un problema generale nelle mappe di pericolosità sismica (Peresan & Panza, 2012) definite secondo il classico approccio probabilistico (probabilistic seismic hazard assessment, PSHA). L’evento si è verificato in un’area classificata a “bassa pericolosità sismica” nella attuale mappa nazionale, pubblicata nel 2004 (Gruppo di Lavoro, 2004). L’ultima revisione della classificazione sismica era stata motivata dal terremoto di S. Giuliano di Puglia del 31/10/2002, avvenuto anch’esso in un’area precedentemente definita a bassa pericolosità sismica. La precedente classificazione era stata a sua volta aggiornata nel 1981-1984, dopo che le precedenti mappe avevano mancato il terremoto dell’Irpinia del 1980. Dunque, sebbene le mappe di pericolosità abbiano l’intento di “prevedere” la pericolosità associata ai possibili terremoti futuri, tali mappe hanno dovuto essere sistematicamente aggiornate dopo aver mancato un forte terremoto. Questo equivale a chiudere il recinto dopo che i buoi sono fuggiti. E’ quindi doveroso chiedersi: a cosa servono tali mappe?

International audience; S U M M A R Y The goal of this study is to investigate the spatial variability of the seismic radiation spectral content of the Sumatra-Andaman 2004 earthquake. We determine the integral estimates of source geometry, duration and rupture propagation given by the stress glut moments of total degree 2 of different source models. These models are constructed from a single or a joint use of different observations including seismology, geodesy, altimetry and tide gauge data. The comparative analysis shows coherency among the different models and no strong contradictions are found between the integral estimates of geodetic and altimetric models, and those retrieved from very long period seismic records (up to 2000-3000 s). The comparison between these results and the integral estimates derived from observed surface wave spectra in period band from 500 to 650 s suggests that the northern part of the fault (to the north of 8 • N near Nicobar Islands) did not radiate long period seismic waves, that is, period shorter than 650 s at least. This conclusion is consistent with the existing composite short and long rise time tsunami model: with short rise time of slip in the southern part of the fault and very long rise time of slip at the northern part. This complex space-time slip evolution can be reproduced by a simple dynamic model of the rupture assuming a crude phenomenological mechanical behaviour of the rupture interface at the fault scales combining an effective slip-controlled exponential weakening effect, related to possible friction and damage breakdown processes of the fault zone, and an effective linear viscous strengthening effect, related to possible interface lubrication processes. While the rupture front speed remains unperturbed with initial short slip duration, a slow creep wave propagates behind the rupture front in the case of viscous effects accounting for the long slip duration and the radiation characteristics in the northern segment.

The joint inversion of Rayleigh wave group velocity dispersion and receiver functions has been used to study the crust and upper mantle structure at eight seismic stations in Cuba. Re- ceiver functions have been computed from teleseismic recordings of earthquakes at epicentral (angular) distances in the range from 30◦ to 90◦ and Rayleigh wave group velocity dispersion relations have been taken from earlier surface wave tomographic studies in the Caribbean area. The thickest crust (∼30 km) below Cuban stations is found at Cascorro (CCC) and Mais ́ı (MAS) whereas the thinnest crust (∼18 km) is found at stations R ́ıo Carpintero (RCC) and Guanta ́namo Bay (GTBY), in the southeastern part of Cuba; this result is in agreement with the southward gradual thinning of the crust revealed by previous studies. In the crystalline crust, the S-wave velocity varies between ∼2.8 and ∼3.9 km s–1 and, at the crust–mantle transition zone, the shear wave velocity varies from ∼4.0 and ∼4.3 km s–1. The lithospheric thickness varies from ∼65 km, in the youngest lithosphere, to ∼150 km in the northeastern part of the Cuban island, below Mais ́ı (MAS) and Moa (MOA) stations. Evidence of a subducted slab possibly belonging to the Caribbean plate is present below the stations Las Mercedes (LMG), RCC and GTBY whereas earlier subducted slabs could explain the results obtained below the Soroa (SOR), Manicaragua (MGV) and Cascorro (CCC) station.

Lessons learnt from the destructive earthquakes occurred during the new millennium provide new opportunities to take action, revise, and improve the procedure for seismic hazard assessment (SHA). A single hazard map cannot meet the requirements from different end-users; the mapping of the expected earthquake ground motion that accounts for events’ recurrence may be suitable for insurances. When dealing with cultural heritage and critical structures (e.g., nuclear power plants), where it is necessary to consider extremely long time intervals, the standard hazard estimates are by far unsuitable, due to their basic heuristic limitations. While time-dependent SHA may be suitable to increase earthquake preparedness, by planning adequate mitigation actions, for critical structures (i.e., those for which the consequences of failure are intolerable) the maximum possible seismic input is relevant. Therefore the need for an appropriate estimate of the seismic hazard, aimed not only at the seismic classification of the national territory, but also at the capability of properly accounting for the local ampli␣cations of ground shaking, as well as for the fault properties, is a pressing concern for seismic engineers. A viable alternative to traditional SHA is represented by the use of the scenario earthquakes, characterized at least in terms of magnitude, distance, and faulting style, and by the treatment of complex source processes. The relevance of the realistic modeling, which permits the generalization of empirical observations by means of physically sound theoretical considerations, is evident, as it allows the optimization of the structural design with respect to the site of interest. The time information associated with the scenarios of ground motion, given by the intermediate-term middle-range earthquake predictions, can be useful to public authorities in assigning priorities for timely mitigation actions. Therefore, the approach we have developed naturally supplies realistic time series of ground motion useful to preserve urban settings, historical monuments, and relevant man-made structures.

The Vrancea region of the south-eastern Carpathians is a remarkable site of intra-continental intermediate- depth seismicity. A large set of geological, geophysical, and geodetic observations has been accumulated for the last few decades and utilised to improve our knowledge of the shallow and deep structures beneath Vran- cea, the crustal and mantle dynamics, and the linkage between deep and surface processes in the region. In this article we review geology and tectonics of the Vrancea region including post-collisional to recent deforma- tions, syn- to post-collisional magmatism, and orogenic exhumation along the East and South Carpathians. The regional seismicity is analysed, and the recent seismic studies including reflection, refraction, body and surface wave tomography are reviewed. We discuss new geodetic measurements of horizontal and vertical movements in the region, geoelectric studies, density/gravity and thermal modelling. Qualitative and quanti- tative (including retrospective) geodynamic models developed for Vrancea are analysed. The knowledge of re- gional tectonics, geodynamics, seismicity, lithospheric deformation, and stress regime in the Vrancea earthquake-prone region assists in an assessment of strong ground motion, seismic hazard and risk. The earth- quake simulation, seismic hazard, and earthquake forecasting models have also been reviewed providing a link between deep geodynamic processes and their manifestation on the surface. Finally we discuss unre- solved problems in Vrancea in order to improve our understanding of the regional evolution, present tecton- ics, mantle dynamics, intermediate-depth seismicity, and surface manifestations of the lithosphere dynamics and to enhance our ability to forecast strong earthquakes in the Vrancea region. The problems to be solved in- clude: (i) the origin of the high-velocity body revealed by seismic tomography studies (oceanic versus conti- nental); (ii) the lithospheric scale mechanism driving the Miocene subsidence of the Transylvania basin; (iii) sub-crustal structure between 40 and 70 km; (iv) contemporary regional horizontal and vertical move- ments; and (v) a comprehensive seismic hazard assessment in the region.

Neo-deterministic seismic hazard assessment. Operational issues are a pressing concern in seismic hazard assessment (SHA), as fatally evidenced by the most destructive recent events worldwide, including the Tohoku (2011) and Haiti (2010) earthquakes (Wyss et al., 2012). A reliable and comprehensive characterization of expected seismic ground shaking, eventually including the related time information, is essential in order to develop effective mitigation strategies and to increase earthquake preparedness (Peresan et al., 2012). Nowadays it is well recognized by the engineering community that standard hazard indicator estimates (e.g. seismic PGA) alone are not sufficient for the adequate design, mainly for special buildings and infrastructures (Field et al., 2000; Zuccolo et al., 2008). Moreover, any effective tool for SHA must demonstrate its capability in anticipating the ground shaking related with large earthquake occurrences, a result that can be attained only through rigorous verification and validation process (Stein et al., 2011, 2012; Peresan and Panza, 2012).

A new methodology for computing synthetic seismograms, complete of the main direct, refracted, converted phases and surface waves, in three – dimensional anelastic lateral heterogeneous media is applied to the modeling of the local records of the 2003 Bam Mw 6.6 Earthquake, South-Eastern Iran. The method is based on the combination of the Modal Summation (MS) technique with the Asymptotic Ray Theory (ART). The three – dimensional models are determined by a set of vertically heterogeneous sections (1D structures) that are juxtaposed on a regular grid. The distribution of these sections in the grid is done in such a way to satisfy the condition of applicability of the WKBJ approximation, i.e. the lateral variation of all the elastic parameters has to be small with respect to the prevailing wavelength. The procedure, described very briefly, has been applied for the area of destructive 26 December 2003 Bam earthquake Mw= 6.6.

The Greater Tehran area is the most important city of Iran and hosts about 20% of the country population. Despite the presence of major faults and the occurrence of historical earthquakes, nowadays the seismicity is relatively quite low and this enhances the use of simulation methods for microzonation and seismic hazard assessment. To simulate the ground motion caused by the 2009, Mw 4 earthquake, occurred south-east of the city, a hybrid technique is used. It combines two methods: the analytical modal summation and the numerical finite difference, taking advantage of the merits of both. The modal summation is applied to simulate wave propagation from the source to the sedimentary basin and finite differences to propagate the incoming wavefield in the laterally heterogeneous part of the structural model that contains the sedimentary basin. Time and frequency domain parameters are simulated along 2 (E-W and SE-NW) profiles for various stations.

The systematic observations of seismic activity on the territory of the Republic of Moldova the influence of strong seismic events generated in Vrancea zone (south-eastern Carpathian Mts.). This fact is used for hazard and risk estimation, which involves show (probabilistic approach, at local and regional scales). The probabilistic approach uses attenuation law as an approximation of the seismic field, and does not consider all source and site effects, therefore, a detailed deterministic analysis is required to fix corrections and gaps for more realistic seismic risk assessment of the territory of the Republic of Moldova. With this purpose as a starting point, we perform a full parametric study for the city of Cahul, located in the southern part of the country, and its surrounding area. The analysis is done in the framework of 1D approximation, i.e. the analyzed region is modeled with a stack of isotropic, homogeneous and inelastic layers. The parametric test shows that the local structure has primary influence on local seismic impact, and geological, tectonic and geophysical data are the key factors, which distinguish the seismic field from site to site. At the regional scale, the seismic wave-field is different from site to site due to the directivity effects of the source. This aspect can be extended in order to perform a more realistic scenario for the entire territory of the Republic of Moldova.

The Vrancea region of the south-eastern Carpathians is a remarkable site of intra-continental intermediate- depth seismicity. A large set of geological, geophysical, and geodetic observations has been accumulated for the last few decades and utilised to improve our knowledge of the shallow and deep structures beneath Vran- cea, the crustal and mantle dynamics, and the linkage between deep and surface processes in the region. In this article we review geology and tectonics of the Vrancea region including post-collisional to recent deforma- tions, syn- to post-collisional magmatism, and orogenic exhumation along the East and South Carpathians. The regional seismicity is analysed, and the recent seismic studies including reflection, refraction, body and surface wave tomography are reviewed. We discuss new geodetic measurements of horizontal and vertical movements in the region, geoelectric studies, density/gravity and thermal modelling. Qualitative and quanti- tative (including retrospective) geodynamic models developed for Vrancea are analysed. The knowledge of re- gional tectonics, geodynamics, seismicity, lithospheric deformation, and stress regime in the Vrancea earthquake-prone region assists in an assessment of strong ground motion, seismic hazard and risk. The earth- quake simulation, seismic hazard, and earthquake forecasting models have also been reviewed providing a link between deep geodynamic processes and their manifestation on the surface. Finally we discuss unre- solved problems in Vrancea in order to improve our understanding of the regional evolution, present tecton- ics, mantle dynamics, intermediate-depth seismicity, and surface manifestations of the lithosphere dynamics and to enhance our ability to forecast strong earthquakes in the Vrancea region. The problems to be solved in- clude: (i) the origin of the high-velocity body revealed by seismic tomography studies (oceanic versus conti- nental); (ii) the lithospheric scale mechanism driving the Miocene subsidence of the Transylvania basin; (iii) sub-crustal structure between 40 and 70 km; (iv) contemporary regional horizontal and vertical move- ments; and (v) a comprehensive seismic hazard assessment in the region.

The coupling/decoupling between the lithosphere and asthenosphere has significant implications for understanding many important aspects of plate tectonics and geodynamics. To drive plate motion, man- tle convection requires coupling at the lithosphere–asthenosphere (LA) interface. Meanwhile a low viscosity layer in the asthenosphere is indicative of possible LA decoupling. Here we present an analytical model of a stratified uppermost mantle structure disturbed by a long-wavelength perturbation (such as the body tide) to analyse the influence of LA viscosity contrast on the growth (or decay) rates of the perturbation. We show that the viscosity contrast of 8–10 orders of magnitude would allow a relative motion of the lithosphere over the asthenosphere due to the long-wavelength perturbations at the rate of about 10 cm yr-1. These constrains on the viscosity contrast can allow to discriminate between the LA coupling and decoupling. The growing seismic and mineralogical evidences of a possible ultra low viscos- ity asthenospheric layer may be indicative of the LA decoupling and their relative motions due to long- wavelength perturbations, and a contribution of the tidal drag on the plate motion should not be neglected in the regions of high viscosity contrasts.

For the protection of cultural heritage and the design of strategic buildings and critical infrastructures, when it is necessary to consider extremely long time intervals, the standard probabilistic estimates of seismic hazard (PSHA) are by far not applicable. The heuristic limitations are, indeed, a major limit of PSHA, whose results, extrapolating ground motion with an infinitely long return period from a few hundreds years of the available earthquake catalogues, may turn out to be a purely numerical artefact. A viable alternative, capable of minimizing the drawbacks of PSHA is represented by the use of a scenario-based methodology, named neo-deterministic approach (NDSHA), which relies on observable data and is based on the physical modelling of seismic waves generation and propagation processes. The NDSHA naturally supplies realistic time series of ground motion, which represent also reliable estimates of ground displacement readily applicable to seismic isolation techniques, useful to preserve historical monuments and relevant man made structures. In addition, an integrated NDSHA approach has been developed that allows for the operational definition of time-dependent scenarios of ground shaking, through the routine updating of formally defined earthquake predictions. The integrated NDSHA procedure, which is currently applied to the Italian territory, combines different pattern recognition techniques, designed for the space-time identification of strong earthquakes, with algorithms for the realistic modelling of ground motion. Accordingly, when an alarm is declared, a set of scenarios of expected ground shaking at bedrock, associated with the alarmed areas identified by means of the algorithms CN and M8S, can be readily computed by means of full waveform modelling, both at regional and local scale, considering all of the possible earthquake sources within the alerted areas. For the relevant sites, further investigations can be performed taking into account the local soil conditions, in order to compute the seismic input (realistic synthetic seismograms) for engineering analysis. The practical application of seismic input modelling for seismic isolation purposes, and particularly for the protection of historical buildings, has been already carried out for example for several sites, including the cities of Trieste (NE Italy) and Valparaiso (Chile) and the towns of Marigliano and Ercolano (Naples, Italy). A recent example of the practical advantages that can be provided by the time-dependent definition of ground-shaking scenarios is given by the Cathedral of Santa Maria di Collemaggio, which was severely damaged during the L’Aquila earthquake (6 April 2009). Based on the ongoing alert for the nearby CN region and the relevant ground shaking expected at the site, the restoration and isolation of the cathedral could have been timely completed, possibly limiting if not preventing the occurred damage. The relevance of the realistic modelling, which permits the generalization of empirical observations by means of physically sound theoretical considerations, is evident, as it allows for the optimisation of the structural design with respect to the site of interest. Moreover, the time information given by the intermediate-term middle-range earthquake prediction can enhance preparedness and planning of risk mitigation actions.

Il seminario annuale del 2011 e l’incontro con la popolazione, tenutisi all’Aquila il 10 e l’11 giugno; la risoluzione «in materia di isolamento sismico delle costruzioni civili e industriali» approvata dall’VIII Commissione della Camera dei Deputati l’8 giugno; l’informazione sul terremoto e maremoto di Tohoku e sull’incidente di Fukushima.

La nuova carta nazionale di pericolosità, caratterizzata da un dettaglio ben superiore a quello consistente coi dati, ed il relativo codice sismico sono basati su metodologie e relativi codici di calcolo che hanno oltre 20 anni e quindi non tengono in debi- to conto i grandi progressi fatti dalla Sismologia.

Il 2011 inizia con due violenti eventi sismici, il primo il 21 febbraio in Nuova Zelanda ed il secondo, ancora più forte e seguito da un devastante tsunami, l’11 marzo in Giappone. Gravi i danni e le distruzioni causate dai due eventi, ma nuove dimostrazioni dell’efficacia dell’isolamento sismico – Le attività già effettuate dal GLIS nel 2011 e quelle previste, anche a seguito degli eventi suddetti.

The lithosphere–asthenosphere system of the Italic region in terms of shear-velocity and density distribution with depth is suitable to investigate the geodynamic context of the region. The velocity structure is obtained through nonlinear inversion of dispersion curves compiled from surface wave tomography on cells 1° × 1° and a smoothing optimization method to choose the representative cellular model, whose layering is used as fixed (a priori) information to obtain a density model by means of linear inversion of gravimetric data. Seismicity and heat flow are used as independent constraints in outlining both the crustal and the seismic lid thickness; the nonlinear moment tensor inversion of recent damaging earthquakes allows some insight in the ongoing kinematic processes. Asymmetry between west-directed (Apennines) and east-directed (Alps, Dinarides) subductions is a robust feature of the velocity model, while density model reveals that slabs are not denser than the ambient mantle, thus supplies no evidence for slab pull.

Ground motion has been computed for the 6 April 2009 earthquake (Mw=6.3) by using a hybrid method (modal summation and finite difference techniques) along a geological section crossing L'Aquilla. Sources have been simulated both as point and extended, with unilateral and bilateral ruptures. Spectral amplifications of about 10 have been found in correspondence of the cover of the Aterno river alluvial deposits and span a wide range of frequencies, that is various typologies of structures. In addition, the modelling has evidenced that whereas strong heterogeneitiies are present, for the same set of synthetic seismograms, the H/V spectral ratios are not able to evidence the spectral amplifications obtained with the 2D/1D response spectra ratios. Possible nonlinear soil effects have been evaluated for PGA values higher than 0.1-0.2 g, depending on the strain-dependent soil properties, with the linear equivalent approach, by using literature variations of shear moduli and damping with strain.

Earth’s CO2 emission in Italy includes both volcanic and non-volcanic degassing, with measured CO2 fluxes of about 35 - 60 Mt/y. Zones of non-volcanic CO2 emission include Tuscany, Latium, Campania, the Apennines, Sicily, and Sardinia. Volcanic emissions are particularly abundant at Mt. Etna in Sicily, but also at Vesuvio, Campi Flegrei, Ischia, Vulcano, and Stromboli, in Central-Southern Italy. The anomalous CO2 emission in Italy is related to the complex geodynamic evolution of this area, in which upper crustal rocks, including carbonate sediments, have been introduced into the upper mantle by Oligocene to present subduction processes. Integrated petrological, geochemical and geophysical data allow us to work out a model for the generation of anomalously high lithospheric CO2 fluxes. Melting of sediments and/or continental crust of the subducted Adriatic-Ionian (African) lithosphere at pressure greater than 4 GPa (130 km) is proposed to represent an efficient mean for deep carbon cycling into the upper mantle and into the exosphere in the Western Mediterranean area. Melting of carbonated lithologies, induced by the progressive rise of mantle temperatures behind the eastward retreating Adriatic-Ionian subducting plate formed a carbonated partially molten CO2-rich mantle in the depth range from 130 km to 70 km. Further upwelling of carbonate-rich melts induces massive outgassing of CO2. Buoyancy forces, probably favored by fluid overpressures, are able to allow migration of CO2 from the mantle to the surface, through deep lithospheric faults, and its accumulation beneath the Moho, and within the lower crust.

Giuliano Panza ha ricevuto la medaglia Beno Gutenberg dalla European Union of Geosciences per “outstanding contributions to Seismology”, la Laurea honoris causa in Fisica dall’Università di Bucarest, la medal of honour della Central European Initiative per gli eccezionali risultati raggiunti dall’Earth Sciences Committee ed è honorary professor presso l’Institute of Geophysics della China Earthquake Administration. Membro eletto della Accademia Nazionale dei Lincei, Academia Europaea, Russian Academy of Sciences, Academy of Sciences for the Developing World e Accademia Nazionale delle Scienze detta dei XL, è autore/coautore di oltre 450 pubblicazio- ni scientifiche nelle più prestigiose riviste internazionali e di oltre 10 libri. È Editor-in-Chief di Earth Sciences Review e Co-Editor di Journal of Seismology and Earthquake Engineering. Qui si riproduce, per il suo interesse sempre attuale e per la chiarez- za dell’esposizione, il testo della Prolusione tenuta in occasione del- l’inaugurazione dell’Anno Accademico 2009-2010 dell’Università di Trieste.

A significant seasonal modulation of seismicity, with a peak in spring and summer, is evidenced in the Himalaya and the Alps, two regions characterized by present day mountain building and glacial retreat. In addition, a secular modulation of seismicity, which can be correlated with surface atmospheric temperature changes in the Northern Hemisphere, is found over the last ten centuries. Therefore, secular variations in permanent glacial dimensions, naturally associated with long-term average surface atmospheric temperature changes, and seasonal snow load may cause crustal deformations that modulate seismicity.

The countries in Central and East Europe are periodically affected by strong earthquakes originating from Vrancea zone and significant seismic effects are recorded all over Romania, Moldova, Ukraine, Bulgaria, Serbia, Hungary, etc. Vrancea earthquakes are of practical and theoretical interest due to the social and economical influence on a vast territory. The main result of this study is the unique collection of intensity data for the Vrancea events of 1940, 1977, 1986, and 1990, which represents a real step forward that overcomes the inherent differences affecting the present-day maps, hampered by political boundaries. This is done adopting a unique modelling procedure and processing the available data in an integrated way. As a result, unified macroseismic maps of the relevant portion of the CEI region are produced using two new procedures, Modified Polynomial Filtering and Diffused Boundary

Una strategia efficace per la mitigazione del rischio sismico richiede la risposta ai seguenti quesiti: a) dove, quando e quanto forte un terremoto può colpire la regione in esame?, b) quali conseguenze ci si deve attendere qualora esso avvenga? La risposta alla prima domanda riguarda la previsione dei terremoti, mentre la seconda è oggetto degli studi di rischio sismico.

Scenari di pericolosità sismica per l' applicazione dell'isolamento sismico.

An integrated neo-deterministic approach to seismic hazard assessment has been developed that combines different pattern recognition techniques, designed for the space-time identification of strong earthquakes, with the procedure for the neo-deterministic assessment of seismic hazard. The integrated approach allows for a time dependent definition of the seismic input (realistic synthetic seismograms), through the routine updating of earthquake predictions. The time information given by the intermediate-term middle-range earthquake prediction can be used to enhance and optimize preparedness actions. Accordingly, when an alarm is declared, ground shaking scenarios at bedrock can be readily computed for the entire alerted area, as well as for the individual areas prone to strong earthquakes included in it, thus providing a reliable and reproducible picture of what should be expected when a strong earthquake occurs. For those sites where intensity values greater than VI (MCS) are estimated at bedrock, further investigations can be performed taking into account the local soil conditions, in order to compute the seismic input (realistic synthetic seismograms) for engineering analysis of relevant structures, such as historical and strategic buildings. A pilot application of the proposed approach, including a detailed evaluation of the expected ground mo-tion accounting for site effects, has been carried out, among others, for the city of Trieste. Attention has been focused on Palazzo Carciotti, a masonry neoclassical palace, which has a prominent artistic relevance within the city. The palace is located in the ancient part of Trieste, where soft superficial sediments of poor geotech-nical characteristics are present. Ground motion modeling shows that these site conditions may lead to a peak ground acceleration value of 0.2 g, greater than the value obtained at bedrock. The computed synthetic seis-mograms have been used as seismic input for the engineering seismic safety appraisal of the building. Three kind of dynamic analysis have been carried out: a) a modal analysis, using response spectrums calculated both from synthetic seismograms and according to Eurocode 8, b) a push-over analysis, c) a dynamic push-over analysis, which have evidenced that a strong earthquake (M=6.5) occurring in the proximity of Trieste (21 km far from the considered site) could seriously compromise the stability of the structure. The realistic computation of the seismic input, taking in account the local soil conditions, combined with the evaluation of the seismic response of buildings provides an effective approach to the assessment seismic risk.

Dalle previsioni a medio termine agli scenari di scuotimento: metodologie di avanguardia per difendersi dai terremoti

The study presents and solves the 2-D elastodynamic model for seismic in-plane wave propagation in laterally inhomogeneous geological profiles imbedded in a vertically inhomogeneous half-space in which an earthquake source is buried. To this end, an efficient hybrid modal summation- boundary integral equation method (MSM-BIEM) is developed and applied. The MSM is used as a tool for simulating wave propagation from the source position to the multilayered laterally inhomogeneous geological profile where the BIEM is applied. The proposed model and the hybrid tool are used to investigate the phenomena of site effects. In fact, such a methodology has the potential to investigate the combined effects of different physical phenomena like surface topography, lateral inhomogeneity and the existence of water saturation in soils on the estimation of site effects. The model and hybrid computational tool developed are applied to contribute to the seismic risk analysis of the Bulgarian capital Sofia.

This paper deals with the neo-deterministic definition of the seismic input in the municipality of Nimis (Italy), aimed at the design of residential seismically isolated buildings. The seismic input is defined by the computation of realistic synthetic seismograms considering different levels of detail for the earthquake source, both for a bedrock model and taking into account the specific site conditions. The horizontal response spectrum, calculated in the centre of the municipality by modelling the most dangerous source, advises against the construction of a building with a fixed base, but it is compatible with the seismic isolation, and it has been, therefore, used for the design of a residential seismically isolated building. The maximum displacement for the isolation system has been estimated about 17 cm, a value much lower than that provided by the code design response spectrum (28 cm). The importance of the realistic modelling, which permits the generalization of empirical observations by means of, physically sound, theoretical considera- tions, is evident, as it allows for the optimisation of the structural design with respect to the site of interest

The main issue of this paper is to show that contrary to many examples of monitored strong earthquakes in different urban areas, the intensity and spectral characteristics of the strong ground motion induced in Bucharest area, by Vrancea intermediate-depth earthquakes, is controlled by the coupled source-site properties rather than by the local site conditions alone. Our results have important implications on the strategy to follow when assessing the seismic microzoning for Bucharest city: we recommend the application of deterministic approaches rather than empirical techniques, like H/V spectral ratios. However, when applied to noise data, the H/V spectral technique succeeds to reproduce the predominant frequency response characteristic for the sedimentary cover beneath the city and the relatively uniform distribution of this structure over the city area. The same technique is clearly inadequate when small earthquakes are considered and our results strongly disagree with any strategy of extrapolation from small and moderate earthquakes to strong earth- quakes for microzoning purposes.

Nimis (Udine) has been included in seismic zone I by the new Italian seismic code, which specifies criteria for the design and construction of new buildings. The study presented in this paper deals with the deterministic definition of the seismic input in the municipality of Nimis, aimed at the design of residential seismic isolated buildings. The seismic input is defined by the computation of synthetic seismograms at different level of detail. In the first approximation a deterministic zoning at national scale has been defined to characterize the ground motion (in terms of displacement, velocity and DGA) at the bedrock. In this way a DGA value consistent with that one provided by the new Italian seismic code is obtained. In a second approximation the detailed modelling of seismic ground motion in Nimis has been performed considering selected scenario earthquakes and the specific local conditions at the site of Nimis. The most dangerous scenario considered, which corresponds to the source of the 1976 Friuli earthquake, leads to a peak ground acceleration al least twice than that obtained at national scale. This demonstrates the relevance of taking into account local geological conditions for a detailed modelling of ground motion. The corresponding horizontal response spectrum, calculated in the centre of the municipality using this source, has been used for the design of a residential seismic isolated building. This spectrum advises against the construction of a building with a fixed base, but it is compatible with the seismic isolation: the maximum displacement for the isolation system has been estimated about 15 cm, a value much lower than that provided by the code design response spectrum (28 cm). The importance of the realistic modelling is evident, as it allows for the optimisation of the structural design with respect to the site of interest.

È stato affrontato il problema della definizione della pericolosità sismica (input sismico) tramite la modellazione dei possibili scenari compatibili con la storia sismica e la sismotettonica della zona di Nimis. I sismogrammi sintetici, che tengono conto dei principi fondamentali della fisica relativi alla generazione e propagazione delle onde sismiche, consentono di colmare le lacune nei dati, inevitabilmente incompleti a causa della limitata finestra temporale coperta dalle osservazioni, rispetto ai tempi dei processi geologici causa dei terremoti. L’elevata sismicità della zona rende complessa la realizzazione di strutture resi- denziali utilizzando tecniche antisismiche tradizionali, mentre risulta particolarmente vantaggioso l’impiego di tecniche avanzate, quali l’isolamento sismico, che consente, nell’ambito della normativa vigente, la realizzazione di costruzioni con interessanti soluzioni architettoniche.