Carlo Doglioni, president of Ingv: "It is an area at risk, the fault of the Apennines that extend"

What is the origin of the Mugello quake? The swarm could go on? Carlo Doglioni, president of the National Institute of Geophysics and Volcanology (Ingv), replies.What caused the earthquake?
The extension of the Apennines, which widens by 3-4 millimeters per year, opening in faults and causing the mountain range to lower. It is the same mechanism that caused the L'Aquila earthquake in 2009 (magnitude 6.3) and the 2016-17 Amatrice-Norcia sequence (magnitude 6.5). Faults are inclined planes that plunge into the earth's crust, in this case to the north-east. One of them moved, causing the earthquake.

There have been over a hundred replies. Is the break in the fault spreading?
So far, the hypocentres of the replicas – ie the breaking points from which the shocks start – have remained confined to a narrow area. When they migrate to a larger surface, they could also involve nearby faults.What does the history of earthquakes in this area teach us?
The magnitude 6.4 earthquake of 1919 had a similar trend: a series of relatively low shocks, which however were followed by a stronger earthquake after one day.

Would a high magnitude like that of 1919 be repeated?
The Mugello is a seismic zone and has potential for an earthquake of magnitude above 6, but we do not know when such a strong shock will be repeated. Nor can we predict how long this sequence will last. In the last 35 years we have had 4 events similar to today, with a magnitude between 4 and 5, and the sequence ended without damage. Not far away, in Garfagnana, we arrived at 6.5, even in that case with minor tremors that preceded the stronger one.

Sometimes the damage is related to the type of soil, not just the energy of the shock. Is this the case with Mugello?
In part of the Mugello the nature of the soil amplifies the shock. It is a basin filled with sediments in quite recent times, in the Plio-Pleistocene, that is, starting from the last 5 million years. They are sandy deposits, of alluvial and lake origin, which accentuate the shocks.

How do you know the layout of the faults?
In Mugello we have little information on the subsoil. The updated geological map is still missing in the area between Barberino and Prato.

So how do you classify that area as at risk?
Based on the history of earthquakes of the past. Then we have the stations of the seismic network. The gps measure how much the ground moves and what are the tectonic deformations of the soil. On the other hand, we cannot afford experiments that are called reflection seismic: a sort of terrain echo that costs about 30 thousand euros per kilometer. Too much for a research institution.

Have you measured the composition of gases or water pressure before and after the earthquake?
Not before. We have no fixed instruments in the area. Then the teams from Florence, Bologna, Pisa and Arezzo started with mobile stations. We have placed 9 extra seismographs and we measure the geochemical signals, including a mud volcano that emits carbon dioxide and methane.

Satellite images do not help you?
Show surface deformations. They only help us indirectly to understand what is happening underground.

Has the cause of the earthquake been the recent shock in Albania?
No, no connection. They are completely different tectonic areas.

Is there a link with the Aquila sequence of the past few days?
Not even. They are independent phenomena, even if linked by the same movement of extension of the Apennines. Faults can be some tens of kilometers long, they certainly cannot be activated at such great distances.

How strong was the Mugello earthquake?
In Italy there are about twenty earthquakes per year of magnitude between 4 and 5. Similar shocks are defined as read. It is unacceptable that today buildings are damaged by such low magnitudes.