31 luglio 2016

Italy's seismicity

Italy is a country with an ancient and long standing/written tradition; knowledge of seismicity is made possible by the large number of documents and information regarding the effects of earthquakes, which in the past have affected different geographical areas of the peninsula. For each area we know the quantity and intensity of the earthquakes, which have taken place in recorded history. This is the first step towards the definition of "seismic hazard", i.e. the definition of one of the elements necessary to evaluate the seismic risk of a territory.

Our country, in the last 2500 years, has been struck by over 30,000 earthquakes of medium and high intensity (greater than IV/V degree of the Mercalli scale), and approximately 560 of VIII intensity or more (approximately one every 4 ½ years).

The twentieth century, has been characterized by 7 earthquakes with a magnitude equal to or greater than 6.5 (classified between X and XI degrees of the Mercalli scale).
Italy is a country with a high seismic risk, characterized by areas more prone to earthquakes of low energy (for example: the Alban Hills south of Rome, Vesuvius area, Etna area), and other areas, where earthquakes occur less frequently but are of higher energy (e.g. Calabria Apennines and Eastern Sicily).

The entire Italian territory except for Sardinia has been struck at least once by an earthquake of I-VI degree on the Mercalli scale i.e. producing only minor damage. Quakes of higher intensity have never struck the Piedmont, a portion of Lombardy and Alto Adige, the Tyrrhenian coast from Versilia to the Volturno River the Adriatic coast south of Ancona (excluding Gargano) and Salento.

The highest seismicity is documented in the central-southern peninsula - along the Apennine ridge which has seen some of the strongest and most destructive events that Italy’s earthquake history has recorded. In the central Apennines, for example, the earthquakes of 1349 and 1703 caused damages to an extensive area including the city of Rome. Vivid memories still linger, not only in the Abruzzo region, but also in Marsica and a vast area of central Italy after the earthquake on 13 January 1915. In the Southern Apennines, the Irpinia region has witnessed, over the centuries, some of the strongest earthquakes in Italian seismic history, including the most recent on 23 November 1980 which left on the territory wounds that are still visible today.

In Calabria and Sicily, the consequences following the earthquakes of 1783, 1693 and 28 December 1908 - one of the strongest recorded seismic events (magnitude 7.2) ever recorded in Italy - are of historical significance, and altered the social fabric, economy and culture of the areas stuck by the earthquake.