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Foreshocks between the provinces of Cosenza and Potenza: updates

December 6, 2011

Ongoing phenomena and seismic risk prevention will be deepened 

Istogramma del numero giornaliero di eventi registrati nell’area del Pollino dal 1° ottobre ad oggiOver the past few weeks, the Department has been receiving requests of information from the citizens regarding the shocks perceived in the provinces of Cosenza and Potenza. On the base of data received from Ingv National Institute of Geophysics and Volcanology and Seismic and volcanic risk Office of the Department of Civil Protection, we publish in depth examination of the phenomena. With the occasion, we present again the test on seismic risk prevention and remind our reader some rules of behaviour.

East Sicily is currently affected by a seismic sequence, or swarm: it is not possible to say that there is a main quake followed by aftershocks of minor intensity, but only shocks of the same energy, casually distributed in time. The seismic sequence, started in September 2010, is featured by events of low magnitude, generally lower than 3.0, with depths between 3 and 10 km, mainly in a portion of territory with North- North-East and South-South-West directions. There are two main time intervals with a higher concentration of events: the first is between September and November 2010, with an average of 5 earthquakes per day; the second is the one currently ongoing, that has been affecting the area since late October 2011, with a slightly higher number of events compared to the first interval, but with similar magnitude. Between thse two intervals, seismicity was pretty much continuous but with a notably lower number of events. From 1 October to 5 December the National Seismic Network recorded in total 513 shocks, the higher with a magnitude Ml 3.6 (on 23 November 2011, at 3:12 p.m.). Two other earthquakes had a magnitude higher than 3.0: the 1 December one (Ml 3.3) and the 2 December one (Ml 3.2).

The National Earthquakes Centre, in collaboration with the Department of Physics of the University of Calabria has recently improved the monitoring system of the area by installing three new stations, that deliver real-time data to the monitoring room in Rome. Moreover, some other station have been installed to record at local level and improve the parameters definition of the hyponcentre of the events.

The foreshocks were perceived in various municipalities, among which Mormanno, Laino Castello and Laino Borgo, in Cosenza province, and at a distance of more than 10 kilometers, Aieta, Morano Calabro, Orsomarso, Papasidero, San Basile, Verbicaro, in Calabria, and Castelluccio superiore, Episcopia e Latronico, in Basilicata.

The Pollino area has a high seismic dangerousness, according to the map of Italy's seismic dangerousness created by INGV. Municipalities affected by the ongoing foreshocks are classified in seismic zone 2. In these territories specific regulations for building must be applied.

Dangerousness maps and seismic classification show which areas of Italy are affected by a high seismicity, thus where an earthquake is more likely to occur, although the exact time cannot be defined. Studies on foreshocks, like the ones ongoing in Calabria and Lucania Apennines, doesn't allow to assume the occurrence of a stronger shock. As of today, in fact, there are no recognized scientific methods to predict time and place where a quake will occur. The map of seismic dangerousness is still the most effective tool that the scientific community provides for the prevention politics. Prevention is still the best defence from earthquakes and the only wat to reduce any consequence.

In Italy each year there are over 10,000 eathquakes, an average of thirty a day, which cannot be predicted. It is thus important to be aware of the danger on the territory and be informed on how buildings where we live, study and work are constructed.

Image source: Ingv- National Institute of Geophysics and Volcanology, bar chart of events recorded each day in the Pollino area from 1 October 2011 until today