Our peninsula has always had to deal with the effects of earthquakes that have hit its territory over the centuries. For this reason, Italy boasts one of the oldest traditions in this regard, think that the first anti-seismic house was designed by Pirro Ligorio back in 1570. On this topic we interviewed Graziano Ferrari, a researcher at the National Institute of Geophysics and Volcanology (INGV) which has reconstructed some of the fundamental stages of the "earthquake culture".
When does the first known seismic catalog in Italy date from?
The first seismic catalog of which we have traces is a manuscript produced following the earthquake in central-southern Italy, which occurred in December 1456. Various events took place on that occasion, of which an overall image remains. The catalog in question is that of Giannozzo Manetti, a manuscript of 1457.
Can we say that Italy has been the forerunner in the field of anti-seismic tradition?
Yes, absolutely. It was precisely in Italy that the first maps with the geography and frequency of destructive earthquakes were created, a sort of ante litteram hazard maps, and the first projects aimed at greater understanding and mitigation of the effects of earthquakes. In 1883, the first "seismic map" of Italy, published by Giuseppe Mercalli, where the areas most subject to destructive events were outlined, followed, in 1888, by the first Italian institutional seismic map, published by the geologist Torquato Taramelli. As regards the scales of macroseismic effects, already in the mid-sixteenth century we have a map with the effects of the earthquake that struck La Bollène-Vésubie, in France, in 1564, represented in the form of symbols of increasing damage, the work of an Italian cartographer no better identified. In their famous study of the earthquake of February 23, 1887, in western Liguria, Mercalli and Taramelli sketched a seismic scale at 10 degrees, modifying the De Rossi - Forel scale, born from the integration of the scales developed respectively by Michele Stefano de Rossi ( 1874) and by François Alphonse Forel.
And from a constructive point of view? When do you start planning taking into account the destructive effects of earthquakes on public and residential buildings?
The first anti-seismic house was designed by Pirro Ligorio, famous architect of Villa d'Este in Tivoli, who after Michelangelo directed the building of San Pietro in the Vatican and was invited to Ferrara in 1568 as court antiquarian. The project dates back to 1570, following the earthquake that struck Ferrara in November. It is a house built with stones and bricks, divided into six rooms, five of which are reinforced at the corners, with massive corner reinforcements on the outside and double brick arches with a stone keystone to protect the openings below. Furthermore, the additional double protection of a lowered brick archway was provided for the windows. Subsequently, following the series of 5 destructive earthquakes which devastated southern Calabria between February and March 1783, the reconstruction of entire towns was planned, with the relocation to areas deemed safer. In that period, the famous "shanty house" was designed, which provided wood as internal reinforcement capable of elastically resisting seismic stresses. Speaking of reconstructions and anti-seismic planning, it is important to remember what happened following the destructive event that struck Norcia on 22 August 1859, with a magnitude of 5.8. Pope Pius IX set up a scientific commission with the aim of establishing effective methods of intervention and reconstruction planning, while correcting the building distortions already present. Two eminent personalities of the time were called, the Modenese architect Luigi Poletti and the Jesuit father Angelo Secchi, then director of the Roman College Observatory. The two scholars elaborated a document on the effects that the earthquake had had on the buildings and on why the buildings had collapsed. Well, it was precisely from the results of this research that a new building law was drawn up consisting of 33 articles which would have bound all construction in the Norcia area. This law also provided for the demolition of the building or a heavy fine in the event of non-application. As part of the same provision, a further project was approved to build an entirely "anti-seismic" district which would take the name of Borgo Pio, in honor of the Pope. Due to the annexation of the city to the Kingdom of Italy, in 1860, this project was never fully realized. However, a whole series of good practices had been implemented, so much so that the city of Norcia, over time, has managed to preserve itself despite the earthquakes that have occurred even in recent times.
Finally, what is meant by seismic risk? What can we do today to make our homes safer?
Seismic risk is the product of three factors: hazard, which expresses the probability that an earthquake of a certain magnitude will occur in a given geographical area in a defined time interval; the exposed value, which indicates the value of the tangible and intangible assets present in a specific area that could potentially be damaged due to the occurrence of an earthquake and their vulnerability. The latter defines the propensity of a building to suffer damage in the event of an earthquake of a given magnitude and is the only factor on which man can act directly to reduce the risk. Today there are various ways to make our homes safer: from the most important and onerous structural reinforcement interventions to more contained but effective interventions for the protection of people such as wallpapers that manage to contain any collapse of the attic, or metal cells mounted inside the room to be protected, an "internal protective box". The latter are just a few examples of the many possible solutions that can protect human lives even when it is not possible to deal with overall interventions on buildings. When building or carrying out renovation works, it is extremely important to be aware of the seismic risk to which one is exposed and to intervene with reference to the seismic legislation in force, which is the result of the great tradition of Italian seismological and engineering studies.
