2023-09-19 05:09:09
by Paolo Virtuani
Davide Piccinini (Ingv): «A fault several kilometers long has been activated in Mugello»
“A fault several kilometers long has been activated.” This is how Davide Piccinini, senior seismologist researcher at the National Institute of Geophysics and Volcanology section of Pisa, answers the question of what caused Monday’s earthquake. «The movement generated an earthquake of magnitude 4.9 at a depth of 8.4 kilometers».
What type of fault came into action and what type of movement did it trigger?
«It is a fault defined as “normal”, i.e. of the extensional type, frequent in the central-northern Apennines. Analyzes are underway to pinpoint specific movements. They are faults that cause an area to subside.”
The entire northern Apennines are extending in a north-eastern direction. Can we say that it is “stretching”?
«Yes, it depends on the movements of the Adriatic plate, which drags with it the external part of the Apennine chain. What happened yesterday is part of the normal dynamics of this part of the Apennines.”
What is the action of the Adriatic plate?
«It is a sort of promontory of the largest African plate that has insinuated itself into the Eurasian one. The Apennines are at the contact between the latter and the Adriatic. In the North, as in Friuli, there are compression movements, on the sides there are relaxation-stretching movements as in Mugello”.
Has the area of Monday’s earthquake had other episodes in the past?
«It is a seismic area where even very strong earthquakes have occurred. As in 1919 with magnitude 6.4 – one of the most important earthquakes of the 20th century in Italy – and in 1542 with magnitude 6.0″.
The main shock at 5.10 was preceded by another about 40 minutes earlier with a magnitude of 3.4. Was it a wake-up call?
«Every year in Italy several thousand earthquakes occur with a magnitude between 3.0 and 4.0 and a few dozen with a magnitude greater than 4.0. Sometimes mainshocks are preceded by what are called foreshocks, but there is no rule. The 1997 Colfiorito earthquake and the 2009 L’Aquila earthquake were preceded by foreshocks, while the 2016 Amatrice earthquake was not. In Mugello there were episodes of magnitude 4-4.5 not preceded by smaller intensity tremors.”
Can we talk about a seismic swarm regarding this event?
«Up until this evening – Monday for those reading this, ed. – there have been around 160 subsequent tremors, of which 25 with a magnitude greater than 2.0. At the moment it is impossible to say how long the earthquake swarm may last.”
Could there be even stronger tremors?
«We can’t rule it out, but we can’t take it for granted either. Every area and every earthquake has its own story.”
In the Adriatic off the coast of the Marche region another seismic swarm has been underway for months. Is there any connection?
«No, they are completely different earthquakes. The one in Mugello was a relaxing earthquake, those in the Adriatic, like the one in Emilia in 2012, are compressive earthquakes.”
Is what happened related to the 2016 earthquakes in Norcia and Amatrice?
«The origin is the same, that is, the movements of the Adriatic plate, but there are no cause-effect relationships. The Norcia and Amatrice earthquakes occurred on completely different faults, not connected to the one that was activated in Mugello. There is no connection even with the earthquakes in Turkey and Morocco.”
There is apprehension in Romagna over the landslides that occurred after the flood. Could the earthquake have mobilized them?
«The energy developed by Monday’s earthquake is low and should not trigger landslides in Romagna, but it is better to check carefully. However, we noticed that the energy did not propagate concentrically around the epicenter, but followed preferential directions, probably due to the characteristics of the fault where the rupture occurred.”
September 18, 2023 (modified September 18, 2023 | 10:12 pm)
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