In the first half of May this year, the Florentine Chianti and the city of Florence itself were affected by a seismic sequence with events up to magnitude 3.7, which alarmed the population. Although it is always thought that the greatest risk for Florence is represented by the floods of the Arno river, it must be said that the Florentine area is not new to seismic phenomena, and in the past it has been hit by even stronger events than those of this year .
On 18 May 1895, in fact, a strong earthquake struck almost the entire province of Florence, causing widespread damage, even serious in some areas. It was one of the strongest earthquakes in Florentine history and also the most recent and documented. To find out what happened that day, and to learn about the characteristics of the event, we interviewed Filippo Bernardini, a geologist at the Bologna branch of INGV, where he deals with macroseismology and historical seismology.
Filippo, what happened on May 18 in Florence?
It was a spring evening and there were many people crowding cafés, taverns and taverns in Florence, a culturally very lively city. At 20:55 there was a very strong earthquake and terrified citizens poured into the street. Rubble fell everywhere and the bells of some churches rang. The newspapers of the time documented the incident and the testimonies were numerous; among these, there were those who claimed to have had the impression of being on a ship in a storm.
In the city the damage was very extensive, but not very serious. There were no great destructions, but almost all the monuments, churches and historic buildings were damaged, including many works of art kept there.
What were the characteristics of this earthquake?
In the context of Italian seismicity, it was a moderate earthquake which, on the basis of the distribution of the effects on the territory, is reported in the historical seismic catalog with a moment magnitude Mw equal to 5.5. It was therefore a smaller event than others that hit our country, such as those in L'Aquila in 2009 or central Italy in 2016. However, the earthquake in Florence represents an emblematic case of what happens when a dangerous average seismic, like that of the area, is combined with a high value of very vulnerable exposed assets: let's think of the building, monumental and artistic heritage of the city. The macroseismic studies carried out in recent decades have led to an evaluation of the overall effects on the city of Florence equal to the seventh degree of the MCS scale (Mercalli-Cancani-Sieberg), while in some areas, such as the hills immediately south of the capital, the damages were major and also reached the eighth degree of the same scale.
How far did the damage extend?
The epicenter seems to be located exactly in the same area of the Florentine Chianti affected by the recent seismic sequence. However, several municipalities and towns in the Florentine district suffered damage, including Lastra a Signa, Signa, San Casciano in Val di Pesa, Impruneta, Bagno a Ripoli and Scandicci. The greatest damage occurred in Grassina, in the municipality of Bagno a Ripoli. In Lappeggi numerous farmhouses collapsed, so much so that they were unusable, as well as a farm near San Martino a Strada. Particularly affected were the churches and historic villas, among these we remember the church of SS. Stefano and Caterina in Pozzolatico, whose bell tower was later demolished as unsafe. Even today, a plaque commemorating the earthquake can be seen inside the church, placed under the altar of the votive chapel dedicated to the Madonna of Loreto. Collapses and upheavals also occurred north of Florence, affecting churches and historic villas throughout the Fiesole hills, from Settignano to the villa-castle of Poggio Gherardo in San Domenico up to the Badia Fiesolana, which was seriously damaged. In Fiesole, on the other hand, minor damage was reported.
The second half of early nineteenth century it was a period marked by great scientific ferment. How was this event studied by the scientific community?
The science that studies earthquakes, Seismology, was in its infancy at the time and there was growing interest in it. The Florentine earthquake of May 1895 occurred precisely in the year of foundation of the Italian Seismological Society, which until 1948 published the "Bulletin of the Italian Seismological Society" annually with a list of all the earthquakes that occurred in our country.
At that time the very first, rudimentary seismographs invented only a few years earlier were already in operation. At the time of the earthquake, around fifty meteorological observatories were active throughout Italy, which at the time were also involved in the study of seismic phenomena, and four of these were located in Florence; all the Florentine observers and many of those scattered throughout the country recorded the earthquake of May 1895 and its aftermaths which, it is estimated, were around fifty.
What are the sources of this earthquake that have come down to us?
The sources are numerous; at the time there were already newspapers, including some titles that are still operational today. The envoys went on site to carry out reconnaissance, which was followed by correspondence full of details and information, which has survived to this day.
Then we have the scientific sources, drawn up by those who studied the seismic phenomenon, and the private ones, such as the reports of damages suffered by the buildings kept in the city archives.
There is no shortage of iconographic sources: some images that have become famous are part of the rich photographic documentation, such as those of the damage suffered by the church of San Martino a Strada (locality of San Martino).
Let's not forget the "traces" still visible today in the area, such as the votive effigies: that of the Madonna del Carmelo, accompanied by a small epigraph in memory of the earthquake, which is located in the historic center of Florence near the Firenze Santa Maria Novella station, and more exactly in via De' Canacci, on the corner with via della Scala; and that of the Madonna di Loreto, located inside the church of Pozzolatico, a small town on the outskirts of Florence, a hamlet in the municipality of Impruneta.
Also in order to illustrate the traces of the 1895 earthquake to the population, in recent years Florence has organized, on the occasion of the day of the national campaign I don't risk an urban trek to discover the signs left by this earthquake and other natural events, such as floods. Transmitting the historical memory of these events to the population is important and helps society to have greater awareness of the natural risks that characterize the area.
Finally, what has this earthquake taught us?
The event of May 18, 1895 reminds us that in Florence, however rare, earthquakes of this kind can occur. It then becomes important to defend the fragility of the city, characterized by an inestimable value of the present artistic heritage and by hundreds of thousands of inhabitants. Although the seismic hazard of the area is medium-low, in fact, the exposed value and vulnerability are very high, and this considerably increases the seismic risk of the whole area; this is an element that both the institutions and administrations (national and local), and the citizens themselves, must know.
To learn more:
Cioppi E. (1995). May 18, 1895: History of a Florentine earthquake. Ximenian Observatory, Florence 1995, 306 pp.