A recent discovery has given today’s seismologists a deeper look into the history of earthquakes—specifically, those that took place in Italy during the 15th century.
Paolo Galli discovered a 15th-century note in a Hebrew prayer book at the Apostolic Vatican Library while searching for information on a separate earthquake from the same period. There are just 450 documented earthquake site observations from Italy from around this time, and about half of those are based on a significant earthquake sequence in 1456 in the south-central Apennines.
According to the study which Galli leads, the note---which is from 1446---describes a previously unknown swarm of earthquakes that had struck the Marche region in the central Apennines and carried on for several months between March and September.
The note, which was written on the leaf of the prayer book, describes how an earthquake around the town of Camerino had knocked down houses, the governor’s courtyard and even destroyed complete cities and villages leaving them as “mound[s] of stone”.
Based on these written observations, Galli believes the earthquake may have measured at about an 8 on the Mercalli-Cancani-Sieberg intensity scale.
“The earthquake of 1456, or rather, the earthquakes of 1456, represent the most catastrophic seismic sequence that occurred in the late Middle Ages in central-southern Italy,” he explained. “Despite the abundance of historical sources, particularly a specific treatise on the earthquake written by the famous humanist Giannozzo Manetti, we still do not have certainties about the different epicentral areas and, therefore, the parameters of individual mainshocks—magnitude and epicenter—and their seismic sources.”
The note added that survivors "come here in Camerino dressed in white pale dresses with their horses and mules and donkeys loaded with bread and food and wine, in order to hold the hand of the poor.”
Galli also found a petition from 1446 asking for funds to restore the city walls and a castle in Petrino, a settlement that is located 20 kilometers (12.5 miles) from Camerino. Galli believes this note may be the only other form of proof to corroborate an earthquake in the area.
"The wealth of historical sources in Italy is undoubtedly one of the richest, but it is equally subject to gaps both in terms of time and in places,” says Galli. “Unlike the Kingdom of Naples, for example, the production of documentation related to earthquakes has certainly been poorer in the Papal States, of which the Marche Region was a part in the 15th century.”
The discovered note, says Galli, “not only helps us partially fill a gap in the seismic history of Italy but also prompts us to reflect on how we still do not know about seismogenesis even in times covered by written sources.”
"Even a single new entry in the catalog, like this one, helps us to understand the seismic cycle occurring in each different region," says Galli, who believes the note will help researchers predict the region's future seismic activity.