Towards the new seismic hazard model of Italy (interview with Carlo Meletti)


In 2004 a small research group, coordinated by INGV, released the Map of Seismic hazard of the Italian territory (MPS04), compiled as required by the Ordinance n. 3274 of the President of the Council of Ministers (2003). The map was to serve as a reference for the Regions, whose task is to update the seismic classification of the respective territories. The map was then made “official” by the Ordinance n. 3519 of the President of the Council of Ministers (28 April 2006) and subsequently published on  the Official Gazette (No. 108 of 11 May 2006).
In the following, other elaborations were added to the map using the same conceptual structure. It  represents the first modern seismic hazard model for Italy. For the first time estimates for different return periods and for various spectral accelerations were released. This model has been then used as the basis for the building code contained in the 2008 Technical Regulations (NTC08), which became operational in 2008 and was also adopted by the 2018 Technical Regulations.
Features and events related to the success of MPS04 are described, among other things, in two posts of this blog:

https://terremotiegrandirischi.com/2016/09/26/che-cose-la-mappa-di-pericolosita-sismica-prima-parte-di-massimiliano-stucchi/
https://terremotiegrandirischi.com/2016/10/05/la-mappa-di-pericolosita-sismica-parte-seconda-usi-abusi-fraintendimenti-di-massimiliano-stucchi/

As usual in many seismic countries, since a few years a research group is compiling a new hazard model, which uses updated data and techniques.
Massimiliano Stucchi discusses about it with Carlo Meletti who, after its important contribution to MPS04, coordinates the new initiative through the INGV Seismic Hazard Center.

MPS04,  even if compiled  “in a hurry” in order to meet the State requirements, had a considerable success, both in the technical-administrative field and – after a few years – at the public level. What drives a new model to be built?

There is the awareness that after more than 10 years we are able to better describe the seismic hazard in Italy. A hazard model is the synthesis of knowledge and data  available at the time of its compilation. In the meantime, we have accumulated a lot of new or updated data (starting from an important revision of not only the historical catalog of earthquakes, but also of the fault and seismogenic sources database, as well as all the accelerometric records of the strong Italian earthquakes of the last 10 years).
Therefore, we decided to check how much the hazard assessment does change. It is a regular practice in the most developed countries (every 6 years in the United States, every 5 in Canada, every 10 in New Zealand). We were driven by a scientific need, but also the Civil Protection Department supported this initiative to verify the potential impact on the building code (seismic classification of municipalities and building regulations).

Can you briefly summarize the phases of this new initiative and anticipate, if possible, the release date of the new model?

Our project started in mid-2015 and we wanted to finish in 2 years. However, our intent was very ambitious: for instance, we involved a very large scientific community (about 150 researchers who, for various reasons, participated). Also the number of activities that we have foreseen was very wide, in how much we wanted to be sure not to neglect any fundamental aspect for the estimate of the hazard. Obviously the intention was to confirm that Italy stands at the same level as the most advanced countries in the world. Because of this reason, deadlines have been postponed respect to the initial project planning. The Department of Civil Protection itself gave priority to the quality of the model rather than to quantity of time necessary to obtain it, given that in the meanwhile the MPS04 model is still considered reliable.
In part,  the process was lengthened because of the continuous interaction with the Great Risks Commission, which assessed the first results during the course of work, suggested changes, and asked for further checks. To this day, we think we are really close to the project conclusion and we can finish by the end of 2018.

Can you anticipate, even without going into detail, if there are any important changes in the distribution of seismic hazard?

In general there is a tendency to have higher acceleration values today than the estimates of the past. Stations located near the faults have recorded accelerations never observed before, for all large earthquakes (also in Italy), due to the increase of number and density of seismic stations worldwide. As a consequence, the ground motion attenuation models have been updated: this now produces higher accelerations compared to the models used in past. This is one of the most important innovations produced by the improvement of available data, in this case the accelerometric recordings.
As for the geographical distribution, compared to the 2004 model, the high seismic hazard areas (Friuli, the entire Apennine chain up to Calabria) will be more restricted and concentrated on the seismogenic structures responsible for the strongest earthquakes. On the other hand, some areas, particularly in Southern Italy, may be a little less dangerous than previously known, thanks to the revision of many data on the seismicity of the past. It is an aspect that we are checking carefully in these weeks.

The new model follows the probabilistic approach like the previous one and like the vast majority of models worldwide. Can you summarize the reasons for this choice?

There is no “unique” seismic hazard but, depending on the use that you want to make, it may be appropriate to use different indicators. The probabilistic approach offers the estimation of expected shaking values from very high to very low probabilities (in other words, it is like saying from frequent to rare). The choice of the parameter to be used for buildings does not concern the hazard danger but the level of safety to be assured to citizens and buildings. The choice is up to the legislator since the size of the economic investment varies. In contrast, the deterministic approach, which defines shaking scenarios for maximum events, provides a single extreme parameter related to a certain event that may not even occur. therefore, the design of buildings could be too burdensome, as engineers have also well explained in this blog.

After each of the most recent earthquakes, rumors claiming that the “map” MPS04 “would underestimate” the seismic hazard for a variety of reasons (approach, models and data used, etc.) raised. Some of these rumors were clearly based on flawed arguments, for example, the type of soil was not taken into account; others just considered the classic “map”, while the MPS04 model offers a variety of seismic hazard assessments that lend themselves to more pondered analyzes. Is that true?

Criticisms might be the proof of the “success” of MPS04. It has become a popular document, very common on the web, and it is shown every time there is talk about earthquakes in Italy. Part of the criticism derives also from our lack of ability to communicate what the values exactly represent and therefore the colors on the map (horizontal acceleration on rigid and horizontal ground, with a certain probability of being exceeded in 10% of cases in 50 years is not the maximum value possible!). On the other side, there are commentators and colleagues who attack the MPS04 model just because they did not take part in its compilation. Unfortunately, most of the times critics are based on wrong or bad faith arguments, or arguments that show how people are not able to grasp the concept of probability. Moreover, when MPS04 came out, it was blasted because its values were considered as too high, whereas after the strong earthquakes of the last 10 years, it is criticized of underestimating data?. They should make up their mind!
It is also worth remembering that a probabilistic model is not evaluated after a single event, but after a significant period of time in which all the events occurred with the model estimates are compared. Finally, I also remember that the current model relies on over 2000 different parameters for each site, precisely to better describe the danger, but people look at only one data (10% in 50 years).

In short, it seems to me that sometimes someone tends to attribute the cause of some collapses to (wrong) seismic hazard assessments, when there should be a discussion on how to build and, perhaps adopt –  the classical reference parameters from an engineering point of view (10% probability of overcoming in 50 years, often assumed as a dogma and never sufficiently explained). Do you agree?

Actually, I am still waiting for someone to show me, a collapsed building that had been designed (correctly) with the NTC08 in Emilia or in central Italy. Then, as a completion to the previous answer, I would like to mention that the PGA parameter used to represent seismic hazard is not used directly to design buildings. It is not the eventual “low” estimated PGA that causes buildings collapse. The PGA is the “Peak Ground Acceleration” that is recorded during an earthquake and it is only one of the many parameters that can be used. For example, a much more significant parameter is the acceleration related to a period of oscillation close to the one of the building.
With reference to the parameters, it is common knowledge that one should always use only 10% of probability of exceeding in 50 years for ordinary buildings. The choice of the value of probability of overcoming is not up to the seismologists, but to the authors of the legislation. In the United States, for example, only the danger with a 2% probability of exceeding in 50 years is taken into consideration. In order to be more precautionary than in the past the code in Italy can decide to use a longer return period and therefore more stringent parameters. Furthermore, it should be remembered that the provisions of the legislation represent the minimum value according to which buildings must be designed: no one forbids the adoption of higher reference values.

The new model does not refer to a formal “normative” request. Can you make any predictions about its possible use?

It is essentially an updated scientific document and it represents what the scientific community can tell about the seismic hazard today in Italy. I insisted on starting this project to show that our knowledge is not blocked at 2004. We would have started much earlier if the model of danger had not been implemented by too little time in the construction regulations.
Its use will essentially depend on the results we will obtain; so it was agreed by the Great Risks Commission in 2015. The differences between the old and the new model will be weigh and if significant will justify changes in the input for the code. The requirements of the new model were however discussed and defined with DPC and the two centers of competence for seismic engineering, namely ReLuis and Eucentre, and with them the future use will be discussed.

The “classical” map MPS04 has been used by many as a “popular” description of the Italian seismic hazard: this has led – through the media but not only – to various exaggerated simplifications (eg: “in areas with low seismic hazard you cannot have very strong earthquakes “), which were the causes of many misunderstandings.
Personally, I have always maintained that the description of the seismic hazard for information purposes requires multiple maps, each dedicated to a different aspect (eg: maximum magnitude, maximum observed intensities etc.), accompanied by well-made explanations. It is also necessary that those who want to get information should devote time and patience to these aspects, avoiding the search for “spots”. Are we in the right direction, in your opinion?

I have always thought that representing the seismic hazard through a map is  an understatement of the complex articulation of the model. But it is also true that that the map is published in the Official Gazette.
When looking at a map, it is easy to misjudge. People tend to compare different places (L’Aquila is worse off than Milan, to give an example), or to think  that the areas we represented with green and light blue were exempt from the possibility of a strong earthquake. It is difficult for us too, but I think we should strive to describe the hazard with several representations at the same time. For example, by using more the seismic hazard curves for a single site, showing the different shaking values with the respective different frequency of exceedance, or with maps that represent the different probabilities of a certain level of shaking, in which it is possible to see that the zero probability of having an earthquake actually in Italy does not exist. In addition to that, the availability of other types of maps would help, such as the one of the maximum magnitude, which is one of the input elements for the seismic hazard.
But first of all we should commit ourselves to better describe this type of work even better and with simpler language. to change the degree of acceptance of the new model.

Come ridurre una volta per tutte il rischio sismico in Italia (di Patrizia Feletig e Enzo Boschi)

In un articolo sul Corriere della Sera lunedì 19 marzo, Milena Gabanelli scrive di copertura assicurativa contro i terremoti ipotizzando un intervento dello Stato come avviene in alcuni paesi esteri, quale alternativa finanziariamente più sostenibile rispetto al risarcimento finanziato con varie “tasse sulla disgrazia”.
Giusto, anche perché i costi per la ricostruzione inseguono una parabola incontrollabile considerato l’aumento della concentrazione di ricchezza per metro quadro. Ma soprattutto con la diffusione di un sistema di copertura assicurativa, gli edifici verrebbero per forza sottoposti a collaudi strutturali. Come dovrebbe essere per attuare la famosa “carta d’identità del fabbricato” rimasta lettera morta. Mentre negli altri paesi europei un fabbricato senza una validazione strutturale non ottiene l’allacciamento di luce, acqua, ecc. in Italia, ci si limita alla verifica formale della sola certificazione energetica del fabbricato in occasione di vendita o locazione!

Una polizza potrebbe allora diventare un incentivo alla prevenzione con la responsabilizzazione delle istituzioni come testimonia la copertura da rischio contro catastrofi naturali francese a partecipazione mista stato-mercato in vigore dal 1982 e incresciosamente non citato nell’articolo! Per non discriminare tra aree ad alto rischio e quelle poco esposte, il premio è fisso, varia invece la franchigia a secondo se il comune dove risiede il fabbricato ha adottato provvedimenti come dei lavori di contenimento di corsi d’acqua o adeguamenti alle norme antisismiche, per contenere la propria esposizione ad alluvioni, terremoti, eruzioni vulcaniche.
Considerando gli otto terremoti più forti che hanno colpito la Penisola negli ultimi 42 anni, non si può non convenire che una polizza contro il sisma sia una misura più che necessaria. Deplorevole che se ne discuta da un quarto di secolo (il primo disegno di legge risale al 1993) e sebbene a volte la proposta sia anche riuscita a spuntare in qualche Finanziaria, è stata velocemente stralciata come fosse l’ennesima gabella impossibile da fare ingoiare al popolo dei proprietari di case.

Ma proprio la politica è doppiamente colpevole.
Primo per il suo irresponsabile fatalismo a ritenere di poter continuare ribaltare sull’iniziativa del singolo la messa in sicurezza delle abitazioni recentemente “incentivata” con la detraibilità fiscale. Il sisma bonus è un lodevole strumento fortemente voluto da Ermete Realacci ma la cui efficacia si scontra con il cronico vizio dei lavori edili in nero.
Secondo, se il 70% del patrimonio immobiliare di un territorio sismico come l’Italia, risulta inadeguato a scosse di medie magnitudo, è anche grazie alla sconsideratezza con la quale gli amministratori locali spesso, non hanno vietato l’edificabilità in aree a rischio. Casamicciola è solo l’ultimo dei tanti casi. Lo stesso vale quando nelle nuove costruzioni o negli interventi di riqualificazione, non hanno fatto rispettare le leggi sulla prevenzione sismica.
Il sindaco di Amatrice è indagato proprio per il crollo di una palazzina che nel 2009 venne evacuata a seguito delle scosse dell’Aquila e, in seguito degli interventi di ripristino, dichiarata dal comune agibile salvo franare la notte del 24 agosto 2016 causando la morte dei suoi abitanti.

Decisamente scellerata poi è la piaga dei condoni, la cui madre di tutte le regolarizzazioni dell’abusivismo è la legge 47 del 1985 del governo Berlusconi. Una sanatoria per la quale grande fu la protesta affinché almeno i territori dichiarati sismici fossero esclusi da questa delittuosa fittizia idoneità assegnata per default all’edificazione precaria, fuori norma, illecita. Sì delittuoso, perché la natura è matrigna ma le vittime dei terremoti sono attribuibili all’abusivismo, alle irregolarità, alla sciatteria, che hanno molti corresponsabili. In un tragico intreccio dove i colpevoli magari finiscono anche per essere loro stessi vittime delle loro azioni o omissioni. Ma questa non è giustizia.

Masonry buildings to the test of Italian earthquakes (interview with Guido Magenes)

…..This comparison with medicine fits very well, there are really many similarities between the work of the technician who has to understand what to do with an existing building and that of the doctor who tries to make a diagnosis and to find a correct therapy for a patient…..


versione italiana qui: Gli edifici in muratura alla prova dei terremoti italiani (colloquio con Guido Magenes)


Guido Magenes is Professor of Structural Engineering at the University of Pavia and IUSS Pavia. He is also the coordinator of the Masonry Structures division of the EUCENTRE Foundation. His area of ​​greatest competence is the seismic behavior of masonry buildings and for this reason he has also participated and still participates in numerous Italian and European technical-regulatory committees.
We discussed with him the behavior of masonry buildings in Italy, with particular reference to what happened during the last earthquakes.

1. The earthquakes of 2016 have determined a sequence of shaking that has put a strain on the buildings of the affected area, especially those in masonry. The effects seen in the field are very different: next to the buildings already heavily damaged by the earthquake of August 24th, there are others that have seen their condition worsen after the shock in October, and others that seem not to have suffered serious damage in all the sequence. Do you have an explanation for this?

 The masonry buildings stock in our country has very variable characteristics and qualities, depending on the era of construction, the materials and construction criteria that were used, the type and architectural form (ordinary buildings or churches, palaces, towers, etc … ), any maintenance and reinforcement or tampering and weakening processes that may have occurred over time. Certainly there are recurrent types of problems, but the diversity of the behavior of masonry buildings, apart from the severity of the shaking (or the different ground motion in the various sites), is  essentially due to this great variability.
Therefore, in the specific case of the seismic sequence of central Italy, which involved a very large area and a considerable variety of buildings, we observed what you say: from the recently built building, of a few storeys, in great part or fully compliant with the modern design and construction criteria, which did not show significant damage, to historic buildings with large spans and heights, such as churches, which tend to be more vulnerable and have therefore suffered great damage and collapse because of their dimensions, geometric ratios and their structural organization. In many if not most cases, also the poor quality of the materials has further worsened the situation.

2. In all the municipalities affected, seismic regulations were in force, with various years of enforcement (the extremes are represented by Amatrice and Accumoli, 1927, and Arquata del Tronto, 1984). The distribution of the damage does not seem to be influenced by these differences; is there a reason?Schermata 2018-02-05 alle 20.44.50Not all regulations are equally effective: a 1927 standard is obviously very different, under many points of view, from a rule of the 1980s or the years 2000s and, as I mentioned above, the buildings built in compliance with the latest rules behaved generally well (constructed with artificial blocks and mortars of good strength, or even stone buildings demolished and rebuilt with good quality mortars). Therefore, I would not say that the distribution of damage is not at all influenced by the regulatory context. It depends on what was written in the norm and how many buildings were built or repaired or reinforced after the introduction of the norm (in the affected centers a significant percentage of the buildings had been built before the seismic regulations that you mentioned).

The rules and design criteria are not necessarily born perfect and they have to adjust, to evolve based on the experience of earthquakes. For example, it is only fifteen or twenty years that we began to recognize that certain types of interventions proposed and widely applied after the earthquakes of Friuli and Basilicata can be harmful or plainly ineffective (think of the infamous reinforced concrete ring beams “in breccia” inserted at intermediate floors in an existing building in stone masonry: in Umbria-Marche ’97 we have begun to see its shortcomings).
In the areas in which the presence of a regulation or a seismic classification seems to have had no effect, it must also be taken into account that the on-site control of the quality of construction and execution, in particular for masonry buildings, were inexistent or ineffective at least until the more recent regulations. The use of a very bad mortar is a recurrent element in many of the old masonry buildings collapsed or damaged in the last seismic sequence. In centers like Accumoli and Amatrice it seems that even where interventions had been carried out on buildings, replacing old floors, for example, or inserting some ties, the problem of poor quality of the masonry had been greatly overlooked, ultimately making the interventions ineffective. We can add that a large part of those areas suffered a considerable depopulation since the early 1900s, with inevitable consequences on the maintenance of buildings, which has led to an increase in widespread vulnerability.

Then there are some particular cases in which historical norms and more recent norms seem to have had a positive effect. Take Norcia’s example: without going into the details of the measurements of the characteristics of the ground motion, it is a fact that Norcia in the last sequence suffered strong shaking, comparable to those of Amatrice and Accumoli but with a much lower damage to buildings. In the history of Norcia there were two very significant events that may have affected  the response of the buildings in the 2016 sequence, one before and one following the 1962 regulations. In 1859 a strong earthquake caused numerous collapses and victims in some areas of the historical center, and following this the Papal State issued a quite effective regulation that gave a series of provisions for repairs and reconstructions: on geometry, in particular on the maximum height of the buildings (two floors), on the construction details, on the quality of materials. Then, in 1979 there was another earthquake in Valnerina, after which other parts of the historic center were damaged, followed by a series of systematic reinforcement measures on many buildings. In many of these buildings the reinforcement of the vertical walls (even with the controversial technique of the reinforced plaster) has remedied one of the main elements of vulnerability, i.e. the weakness/poor quality of the masonry walls. If for a moment we leave aside the elements that can go against the use of reinforced plaster (such as the durability of the intervention), and we see it simply as a technique that has remedied a factor of great vulnerability, we can say that for Norcia there has been a positive combined effect of pre-modern and more recent regional regulations, stemming from the direct experience of seismic events.

3. Let’s  talk about seismic regulations and in particular of their engineering aspects. We hear that they have changed a lot over time, and that perhaps the non-recent ones were not entirely effective. Is it true, and if so why?

As for the engineering component of the regulation, what we now know about the structural and seismic behavior of buildings, in masonry and other structural systems, is the result of a continuous evolution through the experience of earthquakes in Italy and in other parts of the world. In Italy the engineering study of masonry buildings has resumed life, after decades of almost total abandonment, after the 1976 earthquake in Friuli. The first norms/codes that give indications on how to “calculate” a masonry building in Italy date back to the early 80s (to “calculate” I mean “quantitatively assess the level of safety”). Although “calculation” is not the only component of the design, this fact gives the idea of ​​how only the very recent rules have a technical-scientific basis aligned with current knowledge. I would like to say that the absence of calculation in a project does not necessarily imply that the building is unsafe: in the past we followed geometric and constructive rules of an empirical type, based on the experience and intuition of the mechanical behavior, although not explicated in detailed calculations. Even today, for the design of a simple and regular masonry building, it is possible to follow codified geometrical and constructive rules that avoid detailed or complex calculations, but still achieve an adequate level of safety.
The experience of the earthquakes of Irpinia, Umbria-Marche, until the most recent in central Italy, have been a continuous test and a source of knowledge. For example, as mentioned in my answer to the previous question, the Umbria-Marche 1997 earthquake, besides highlighting the great vulnerability of churches and of certain historical structures, has been an important test for strengthening criteria and techniques on masonry buildings that were proposed and developed following the Italian earthquakes of the late ’70s, showing how some techniques are not very effective or can even be harmful if applied indiscriminately and without awareness

To conclude my answer with my opinion on current technical standards, I think that as regards the design of new buildings we are really at a very advanced state of progress, which effectively attains the levels of safety that today are considered adequate. I think there are more uncertainties on the assessment and strengthening of existing buildings, even if it is not so much a regulatory problem but rather of scientific knowledge and of the correct identification of strategies and techniques for the intervention. It is certainly easier to design and build a seismic-resistant building from scratch, than to assess and intervene on an existing building.

4. How much – and how – does the construction and detailing of a building affect its seismic safety, beyond the design?

The question gives me the opportunity to dwell a little more on what is meant by “design”, which is something different from the mere “calculation”. The design includes all aspects of overall conception, choice and organization of the structure, choice of materials and construction techniques (with the awareness of how they can and should be executed in situ), performance verification calculations in terms of safety against collapse and of satisfactory behavior in normal operation, prescriptions on construction details. In modern seismic design it is also necessary to take into account, when relevant, the seismic response of the non-structural parts of the construction. There must also be a check that what is prescribed in the design is actually implemented during construction.

The calculation is therefore only a component of the design. It is interesting to note that most of the existing masonry buildings were not calculated, at least as we understand structural calculations now. The first Italian national technical standard on masonry constructions with a sufficiently detailed description of the calculations for the structural verification dates back to 1987. Technical standards with indications for the seismic calculation, were issued after the earthquake of Friuli 1976 and in subsequent times. Before those norms, a technical literature and manuals existed, with reference to the principles of mechanics, as well as a building tradition. I would like to clarify that here I am talking about regulations/norms that tell how to calculate the resistance of a masonry building, subject to seismic or non-seismic actions. Just to give an example, the Royal Decree of 1909 (post earthquake of Messina), a historical milestone as regards seismic regulations, gives criteria to define the seismic action, gives constructive and geometric rules but does not tell how to calculate the resistance (the capacity, according to the modern technical language) of a masonry building.

The constructive tradition based on the respect of the “rule of art” always had in mind the importance of construction details, of the quality of the materials, of how the building is built, and this has allowed and allows well-constructed buildings (but not “calculated”, i.e. non-engineered) to withstand even very violent seismic shocks. In modern buildings, the compliance during construction site of the execution rules, the control of the quality of the materials, is equally important, although this holds for masonry as for the other types of construction. The sensitivity of the structure to constructional defects is a function of the level of robustness of the structural system. A masonry box-like construction, strongly hyperstatic (i.e. where the number of resistant elements is higher than the minimum necessary to ensure equilibrium under the applied loads) could in principle be less sensitive to construction defects than an isostatic prefabricated structure (i.e. where the number of resistant elements is just equal to the minimum necessary to ensure equilibrium under the applied loads, so that the failure of a single element is sufficient to generate a collapse). Obviously we are talking about local defects and not generalized over the whole construction. If all materials are poor quality throughout the construction, then it is a great problem, but not necessarily a masonry building is more sensitive to such problem than, say, a reinforced concrete frame, in which also defects in the reinforcement detailing are possible (for instance in beam-column joints or in lap splices or in anchorage of rebars and so forth).

5. Many surveyors in post-earthquake reconnaissance activities have found traces of interventions that have allegedly weakened the structures. Do you agree?

In post-earthquake surveys, carried out quickly in emergency conditions, it is not always possible to clearly understand the history of the building and what changes have been made, in what time and modalities, but sometimes it is clear that some modifications to the construction have been detrimental to safety. Often these are interventions that were made with total unawareness of the effects on structural safety and purely for the purpose of use and redistribution of space. In other cases, more rare, there are also interventions made with “structural” purposes, perhaps even with the idea of ​​achieving an increase in safety, but which in reality were harmful or ineffective. A classic example, often discussed in the literature also on the basis of the Italian post-earthquake recognitions from Umbria-Marche 1997 onwards, is the insertion of new, rigid and heavy structural elements (such as the replacement of a wooden floor with a reinforced concrete floor) in a building with very weak masonry (for example masonry made of irregular stones with poor mortar), without the masonry being properly consolidated. There was a period, following the earthquakes of Friuli and Irpinia, where much emphasis was given to the fact that rigid diaphragms (i.e. the floors and roofs) increase the hyperstaticity, hence the robustness of the construction and the so-called “box behaviour”, by which engineers tried to replicate in existing structures something that is relatively simple to implement, and whose effects are well controllable, in new constructions, but which in an existing construction has great problems of practical implementation (particularly in the connection between new elements and existing elements) and of potentially negative structural effects (increase of stresses in an already weak masonry). It is important to note that the effectiveness of the interventions is tested by earthquakes that take place in later times, and in some areas of central Italy it has been possible to draw indications of this kind. In the earthquake of Umbria-Marche in 1997 it was possible to observe various problematic situations in buildings where the existing floors had been replaced by heavier and more rigid slabs.

Allow me, however, to add a further comment. From the scientific point of view, the fact that an intervention is “harmful” or weakens the structure compared to the non-intervention is verifiable experimentally only if there is a confirmation of what would happen to the building without intervening and what would happen following the intervention . This type of comparison in the vast majority of practical cases  is not possible, except for very fortunate cases of almost identical buildings built on the same ground where one was reinforced and the other not, or that were reinforced with different methods. Or through laboratory experiments, comparing specimens tested on a “shaking table” (earthquake simulator). So, in general I am always rather skeptical of interpretations given on the basis of purely visual rapid surveys, without the necessary in-depth study of the details and without a quantitative analysis carried out in a competent and thorough manner.
I can say (and I know that many colleagues have a similar opinion) that in many cases seen in central Italy the collapse of the construction would have taken place regardless of the type of floor, light or heavy, rigid or flexible, by virtue of the bad quality of the masonry, which appeared to be the main problem.

6. How did the repetition of the strong shocks play in the aggravation of the damage (where it occurred)? Is it something that is implicitly foreseen, and taken care of, by the seismic norms? On the other hand, how do you explain the numerous cases of almost total absence of damage?

The repeated shaking aggravates the damage, the more the damage caused by the previous shock is serious. It seems a rather obvious statement, but essentially it is what happens. For example, if a first shock on a masonry building generates only a few cracks, not very wide and of a certain type (for example horizontal cracks, which close after the shock due to selfweight), the building has not lost much of its resistance; so if it is subjected to repeated shaking, less intense than the first shock, it is possible that the damage does not get too much worse, and if it is subjected to a shaking stronger than the first shock it will have a resistance equal to or slightly less than it would have if the first shock had not been there. On the other hand, if a shock leads to the development of diagonal cracks (so-called “shear cracks”) or vertical cracks with spalling, the damaged part has lost a significant portion of its ability to resist and subsequent repeated shaking can lead to progressive degradation and collapse, even if the subsequent shocks suffered by the building, individually, are perhaps less strong than the first one. This is something visible and reproducible also in the laboratory.

That said, there are types of constructions and structural elements that are more or less sensitive to the repetition of the seismic action. When seismic engineers speak of “ductility” of the structure or of a mechanism, they also refer to the ability of a structure to resist repeated loading cycles well beyond the threshold of the first crack or the first visible damage, without reaching collapse. A well-designed modern reinforced concrete construction is a structure of this type, for example. Unreinforced masonry, on the other hand, is more susceptible to damage induced by the repetition of loading cycles beyond cracking. As a consequence, existing masonry buildings, once damaged by a first shock, are more vulnerable to subsequent shocks. On the other hand, if the first shock does not cause significant damage, the safety of the building remains, in most cases, more or less unchanged and this accounts for the fact that numerous masonry constructions have also resisted repeated shocks. Unfortunately, sometimes the damage may not be clearly visible. Damage in masonry originates in the form of micro-cracks (not visible to the naked eye) which then develop into macro-cracks. If in a laboratory test a sample of masonry is pushed to a condition very close to the onset of the macro-cracks but the load is removed just before they develop, it may happen that in a subsequent loading phase the macro-cracks develop at a load level lower than that achieved in the first phase. It may therefore happen that a building that has resisted a violent shock without apparent damage is visibly damaged by a subsequent shock less violent than the first.

You ask me if the behavior of the structure under repeated shocks is implicitly considered in the seismic norms: the answer is yes, at least for certain aspects. For example, the respect of certain construction details in reinforced concrete and the application of certain rules in the sizing of the sections and of the reinforcement have this purpose: to make the structure less susceptible to damage under repeated actions. Moreover, less ductile structures, such as those in unreinforced masonry, are designed with higher seismic “loads” than the more ductile structures, also to compensate their greater susceptibility to degradation due to repeated action. However, there are some aspects of the problem of resistance and accumulation of damage under repeated shaking that remain to be explored and are still cutting-edge research topics. In particular, if it is true that theoretical models are becoming available to assess how the risk (i.e. the probability of collapse or damage) evolves in a building or a group of buildings as time passes and seismic shocks occur, these models must still be refined to give results that are quantitatively reliable.

7. It seems to me that the variety of masonry buildings, at least in Italy, is really large: so large that knowing them requires an approach similar to that of medicine, where each case has its own peculiarities. Therefore, there is perhaps no universal therapy, every case requires a specific care: is it correct? And if so, given that the building and construction techniques and quality of different areas of the Apennines (and others) are similar to those of the areas affected in 2016, should a similar destruction be expected to repeat again?

This comparison with medicine fits very well, there are really many similarities between the work of the technician who has to understand what to do with an existing building and that of the doctor who tries to make a diagnosis and to find a correct therapy for a patient. From the technical point of view there is no universal therapy and no (good) doctor would be able to apply a therapeutic protocol without the anamnesis, the objective examination, any necessary instrumental or laboratory tests and the formulation of a diagnosis (which tells us what is the patient’s disease / health status, and then defines what he needs, the therapy). The good technician follows a similar path to arrive at the evaluation of safety and possible hypotheses of intervention (or not intervention). Of course it is possible and necessary, as is the case for medicine and public health, to define strategies and policies for prioritization and allocation of resources to ensure that the overall seismic risk in our country decreases. Certainly, where the old buildings have not been subject to maintenance, or just to aesthetic and functional maintenance without structural reinforcement, we can expect destructions similar to those seen in 2016 on the occasion of future earthquakes of comparable magnitude. This applies to both public and private buildings.

Where instead we have intervened or will intervene in a conscious way, paying attention to the problem of seismic safety, the level of damage to be expected is  lower, as the experience of the past earthquakes teaches us.
Allow me to conclude this interview with some non-purely technical engineering comments. The possibility of reducing the seismic risk in Italy depends on many factors, ranging from how politics govern the problem of natural hazards, to how technicians, individually and collectively, interact and communicate with politics, to how the presence of risk is communicated to the population, to how, as a consequence,  the citizen makes his choices when he buys or takes decisions to maintain a property. In my opinion it is necessary to progressively evolve into a system in which the citizen recognizes that it is in his own interest to pursue a higher seismic safety, initially spending a little more, because he will have a return in the future not only in terms of safety but also of economic benefit, for example in the market value of his property. The “Sismabonus” initiative is certainly a first step in this direction, but other steps will have to be taken. The goal, certainly not easy to achieve, should be that the safety level of a building has a clear and recognized economic market value, and I think this would work for both the small owner and for real estate investors. I know that some are scared by this perspective, but personally I think that, at least for what concerns privately owned real estate and facilities, there are no other ways to achieve, within a few decades, a substantial and widespread reduction of seismic risk in Italy.

 

Sopra i nostri piedi – Above our feet (di M. Stucchi)

(english version below)

Questo titolo prende manifestamente spunto da quello del bellissimo volume di Alessandro Amato: “Sotto i nostri piedi”, arrivato alla seconda ristampa (con integrazione sulla sequenza sismica del 2016 in Centro Italia) e in distribuzione nelle edicole con “Le Scienze”, dopo che l’autore è stato finalista del Premio Letterario Galileo 2017.

Il volume di Amato tratta di sismologia, previsione dei terremoti, aspetti scientifici, culturali e politici. I sismologi si occupano di descrivere, nel miglior modo possibile, come si generano i terremoti e come le onde sismiche si propagano nella Terra; il tutto, appunto, sotto i nostri piedi. Alcuni sismologi si occupano, in una specie di terra di confine dove operano anche alcuni ingegneri, di descrivere come le onde sismiche interagiscono con la superficie del terreno e con gli edifici: quindi, di fornire la descrizione del moto del suolo nelle modalità più adatte all’ingegneria sismica. Questa terra di confine si chiama in inglese “engineering seismology”, le cui possibili traduzioni italiane suonano tutte male. Una Sezione dell’INGV, quella di Milano, si occupa in prevalenza di questi aspetti ed era denominata “Sismologia Applicata”; tempo fa aveva ricercato una collaborazione stretta, istituzionale, con la Fondazione Eucentre di Pavia, alla cui costituzione INGV aveva peraltro contribuito come socio fondatore, sia pure con poco merito e ancor meno investimento. Continua a leggere

Ischia, Torre Annunziata, perception of risk and magnitude (M. Stucchi)

This is a quick translation from the Italian version, with the help of Google. Sorry for the imperfect English. Thanks to Ina Cecic for her prompt review.

Italy was beginning to remember the anniversary of Amatrice’s earthquake (August 24, 2016) in different ways, of course, when the Ischia earthquake dramatically reopened the problem of so-called prevention, of which so much has been said and spoken about.
On the morning of the 21st, the day of the earthquake, Minister Del Rio had spoken at the Rimini (Comunione and Liberazione) meeting. Del Rio is a Minister of a couple of governments I do not like, but among the many is a person I trust. After (unfortunately) reproposing a “pearl” that must have remained in his pocket since the earthquakes of 2012 (“the area was not known as seismic“, ignoring the work done by the Emilia and Romagna Region to delay as much as possible the affiliation to a seismic zone of much of its territory), he recalled, illustrated and defended the so-called “sismabonus” and the initiatives of “Casa Italia”, also reminding that the solution of the problems is not for tomorrow. Stimulated by some interlocutors, he also pushed further on, talking about the necessity of the “building dossier” and of demolitions, where necessary. Ohibò! Continua a leggere

Earthquakes and Great Risks: a blog 2014-2015 (M. Stucchi)

https://terremotiegrandirischi.com/english/

“Earthquakes and Great Risks” è stato, a partire dall’ottobre 2014, il cugino di lingua inglese di questo blog. E’ nato soprattutto per fornire al lettore internazionale la versione “corretta” dei fatti legati al processo “Grandi Rischi”, a fronte di una diffusione impressionante di informazioni e interpretazioni che possiamo definire inesatte – nel migliore dei casi.
Il blog ha contenuto una ventina di post, parte dei quali – a cura di G. Cavallo e di M. Stucchi – dedicati a fare chiarezza su quanto sopra, e parte a fornire una cronaca, quasi in diretta, del processo d’Appello.
E’ stato letto da qualche migliaia di lettori provenienti da 98 nazioni (vedi  mappa).

Schermata 2017-08-02 alle 15.44.13

Rileggendolo oggi, a parte le imprecisioni e gli inevitabili errori di lingua, si ha l’impressione che abbia fornito una analisi attenta e circostanziata – forse più che in questo stesso blog – dei principali “pitfalls” riguardanti il processo sulla base dei quali sono stati costruiti numerosi articoli internazionali, anche su riviste “peer reviewed”, scritti anche da illustri colleghi. Questo sforzo è stato riconosciuto da diversi lettori.

Per non perdere questi contenuti il blog, che verrà chiuso a breve, è stato  salvato nella sezione “English material”.

La vicenda processuale alla prova del romanzo. Luci e ombre del volume “La causalità psichica nei reati colposi” di Marco Billi (di Cecilia Valbonesi)

Cecilia Valbonesi è Dottore di ricerca in Diritto penale presso l’Università degli Studi di Firenze e Avvocato del Foro di Firenze. Per motivi scientifici ha seguito e commentato il cosiddetto  processo Grandi Rischi. In ultimo si veda “Terremoti colposi e terremoto della colpa: riflessioni a margine  della sentenza “Grandi Rischi”, in Rivista Italiana di Diritto e Procedura Penale, 2016, n. 3, p. 1498.
Le abbiamo chiesto un commento al volume – uscito lo scorso marzo – del Giudice di primo grado del processo stesso, Marco Billi.

Di recente, il copioso panorama letterario sulla vicenda giudiziaria relativa alle responsabilità della c.d. Commissione Grandi Rischi si è arricchito di un nuovo volume dal titolo “La causalità psichica nei reati colposi”.
L’ambizioso progetto reca la firma del Giudice estensore della prima sentenza di merito (Tribunale di L’Aquila, 22/10/2012, n. 380) che, accogliendo pienamente le prospettazioni accusatorie, ha condannato per omicidio colposo plurimo e lesioni colpose i sette scienziati i quali, a suo giudizio, “componevano la Commissione Grandi Rischi” della Protezione civile nella riunione del 31 marzo 2009. The L’Aquila Seven  furono ritenuti responsabili di quella scorretta valutazione e informazione sul rischio sismico che avrebbe cagionato la morte ed il ferimento di 29 cittadini (13 secondo la Corte d’Appello e la Corte di Cassazione)  rimasti schiacciati sotto le macerie delle proprie case. Continua a leggere

Terremoti, esposizione e assicurazioni (di P. Feletig e A. Boschi)

Di tutti paesi dell’Europa l’Italia è il paese più esposto alle catastrofi. Terremoti, alluvioni, frane, maremoti, avversità atmosferiche eccezionali di ogni sorta, colpiscono regolarmente il Belpaese che deve mettere in conto dai 3-3,5 miliardi annui  di danni materiali. In media, perché se succede “the Big One”, ovvero l’evento con ricorrenza ogni 200 anni allora le perdite economiche causate da calamità schizzano molto in alto.

Per esempio, incrociando la storia sismica nazionale con gli strumenti parametrici di sofisticati modelli si ricavano proiezioni da brivido. Secondo una simulazione della società svizzera di riassicurazione Swiss Re, un terremoto di magnitudo 6.2 (come quello di Amatrice) nell’area di Parma potrebbe causare perdite per 53 miliardi di euro. A titolo di confronto, considerate che gli 8 rilevanti terremoti (escluso quello dell’ultima settimana) avvenuti negli ultimi 40 anni sulla Penisola hanno totalizzato danni per 60 miliardi di euro circa.
Per completare queste fosche statistiche bisogna sapere che, dal 1970 ad oggi, 7 dei 10 terremoti  più costosi d’Europa si sono verificati in Italia paese doppiamente esposto sia per la vulnerabilità del suo patrimonio artistico che per le costruzioni edificate in assenza o in barba alla normativa antisisimica. Aspetto che dovrebbe far riflettere sulla concessione  del governo di assicurare il risarcimento a tutti, comunque e nonostante le responsabilità precise di taluni, pubblico o privato che siano.

L’indesiderabile primato italiano di esposizione alle catastrofi naturali si accompagna di un’aggravante: risarcire costerà sempre di più. Si accresce il valore concentrato su ogni metro quadro. E’ un trend in accelerazione confermano nel settore assicurativo. Del resto basta paragonare i macchinari di una filanda con quelli di una fabbrica 4.0 di oggi; ma più semplicemente, basta il confronto tra la concentrazione edilizia ai tempi dei nostri nonni e quella di adesso o, ancora, tra gli elettrodomestici contenuti nella casa dei genitori e le apparecchiature elettroniche mediamente possedute oggi.
E’ evidente che con questo aumento vertiginoso dell’esposizione, indennizzare con il solo intervento dello Stato non può reggere alla lunga. Non sono solo le casse pubbliche a non farcela ma finisce per azzopparsi l’intero sistema paese con ripercussioni sulle valutazioni delle società di rating. Si calcola che un evento catastrofale con ritorno, ossia che avviene statisticamente ogni 250 anni può arrivare a produrre una retrocessione di quasi un punto.

C’è poi una prospettiva macro che va tenuta in considerazione. “Le misure di prevenzione e gli interventi strutturali antisismici sono fondamentali e imprescindibili ma neppure così il rischio può essere completamente annullato, in particolare quello di natura economico-finanziaria. Una grande calamità catastrofale, inoltre, sconvolge il sistema economico produttivo del Paese, mette a dura prova la sua resilienza, impatta sul PIL. Magari salviamo la vita ma perdiamo casa e lavoro: di qui l’importanza di una gestione del rischio ex-ante combinando prevenzione anti-sismica e copertura finanziaria-assicurativa” spiega Marco Coletta a capo di una compagnia di riassicurazione con 150 anni di attività alle spalle, sottolineando il deficit di protezione assicurativa in Italia.
Le PMI (Piccole e Medie Imprese) sono largamente sottoassicurate contro catastrofi naturali e poco più di 1% degli immobili residenziali è coperto. La penetrazione assicurativa del ramo danni non-auto misurata in volume dei premi danni non auto in rapporto al PIL in Italia è pari a 0,9%, in Francia a 2,4%, in Germania a 2,5% e mediamente sopra 2% in tutti gli altri paesi europei dove il meccanismo di mutualità permette di correggere l’incidenza economica del premio sul portatore di rischio più alto. Pagando tutti, pagheremmo molto meno.
“Con una penetrazione superiore a 90% si avrebbero premi medi di 100 euro l’anno. Ma c’è un problema culturale” riconoscono alcuni assicuratori che non nascondono la difficoltà di far accettare un concetto di obbligatorietà a consumatori già guardinghi con l’obbligo del RC auto e professionali e auspica una campagna di sensibilizzazione promossa dal governo. Singolare la modesta attenzione del legislatore alla funzione sociale della copertura assicurativa contro inondazioni e terremoti in un paese come l’Italia. Non godono di nessun incentivo fiscale: non sono deducibili nella dichiarazione dei redditi (come invece avviene per le polizze vita) e l’Iva è alta ( 22,25%). Gli schemi di copertura potrebbero prevedere una cooperazione tra pubblico e privato. Lo Stato potrebbe assumere il ruolo di riassicuratore in ultima istanza, dove per esempio le compagnie private coprono fino a concorrenza di un importo alto, oltre a quella soglia (caso meno probabile) interverrebbe lo Stato che potrebbe, per esempio, coprirsi con operazioni di cartolarizzazione di immobili pubblici.

Se il terremoto dell’Irpinia dove i primi soccorritori ad arrivare sul posto furono operai specializzati inviati dal sindacato, ha portato alla nascita della Protezione Civile, possiamo sperare che questi ultimi sismi in Centro Italia, portino a soluzioni efficienti e finanziariamente sostenibili di risarcimento dei danni economici da calamità naturali?

Continua a leggere

Il fatto che non sussiste non è stato commesso (di Giacomo Cavallo)

Con l’assoluzione del Dott. Bertolaso, anche in attesa delle motovazioni, spero che finalmente si possa dire conclusa la vicenda “processuale” della riunione di esperti che ha preceduto il Terremoto dell’Aquila – a meno che i colpevolisti non si ostinino a buttare via tempo e denaro per creare processi che non hanno ragion d’essere, con il compito di giudicare reati inesistenti, dimenticando le sentenze della Corte di Cassazione e soprattutto d’Appello, ma anche parte della sentenza di primo grado. Continua a leggere