Other eighteen-shock over magnitude 4 in the twenty four hours after the main. And a possible lowering of the soil "up to 70 cm", as announced by the Ingv at'Ansa, and is visible by looking at two shots of the mount Carrier appeared on the site geologists.en a few hours after the earthquake. The earthquake and the consequence of an event, which, he says Alessandro Amato, seismologist of theNew, "has surprised us". A first analysis of the data by the national Institute of geophysics and volcanology (ingv), however, bodes well, because it is not a question of the ' awakening' new fault but the detachment of a piece of that already attivatasi at the end of August. A scenario comforting under the scientific but that does not exclude the options that there is still energy to unleash in a short period of time. It’s all the fault of the removal of the tyrrhenian coast from the adriatic sea, a phenomenon which is slow, but constant, source of the 70 days that have devastated the lands on the border between Lazio, Brands and Umbria.
Alessandro Amato, what is happening along the Apennines?
You have to start from a remote cause. There is a geological process that lasts up to several hundreds of thousands of years: the stretching of the earth’s crust. The Apennines are extending from the Adriatic to the Tyrrhenian sea. We see from the gps. The two parts separate at an average speed of about 5 millimeters every year. This is the engine, the effects were the earthquakes of the last two months, likely related to the rotation of the microplacca of the adriatic which pushes against the Alps and the southern part of this that rotates counter-clockwise. We are still in the field of hypothesis, this is the most probable.
What happened in the last two months?
The deformation process is continuous. Let’s take an example: five millimeters per year, involving over two centuries, a deformation of a meter. The faults, which are branched, and the complex between the Calabria and the Plain of the Po, resist this 'stretching', because they have an friction. When, however, the enlargement 'beats' the resistance, these moving in just a few seconds of space that had not covered in the previous two centuries. The length of the piece of the fault that moves depends on the magnitude of the earthquake. In August and in the past few days we speak about a fault of about 20 miles. In Irpinia, in 1980 and in Avezzano at the beginning of '900 and moves in a normal fault of about 40 km, generating earthquakes of magnitude 7.
Why is the border between Lazio, Umbria and Marche there have been four earthquakes so strong in so little time?
The first earthquake of magnitude 6 has caused a shift in the order of a maximum of one meter in the direction south-south-east and north-north-west. The system was followed by many aftershock (earthquakes smaller in the following days, ed.). The movement of this fault has disrupted the parts of the fault around. It is as if the displacement of the August 24, had whetted the fault nearest. This then it is probably move on before would have done.
let’s Talk about the two earthquakes of last Wednesday?
Yes, the two earthquakes of magnitude 5.4 and 5.9 can be explained as well. Why are the past two months, is unknown: these activations subsequent to a fault – and we know many, historically, have variable times. We go from minutes to days to months, as in the case of the apennines. All we thought at that point that the stored energy from the 'remote cause' of which we spoke at the beginning it had been completely unloaded.
The take place, however, is back to shake the 30th of October, with a shock more powerful than all the others. Why?
We are waiting for the data of the satellites, which are likely to be decisive because we will see exactly the horizontal and vertical movements. Stress where it begins and where it ends in the rupture of the fault that occurred on Sunday morning. What is certain is that we were amazed. We already know, indeed, that the rupture of the October 30, reprises that of 24 August – which occurred from the town of Amatrice, Accumoli and Norcia – Norcia-Visso of the previous days. The last earthquake had its origin in the middle of the other two and it has activated a fault of 20-25 km, nearly 30, ranging from a little to the north of the epicenter to the south, towards the town of Amatrice. At the moment, the most plausible explanation is that the part of the fault that moved on the 24th of August it had not slipped completely, continuing in the last few hours of his landslide. The data processing seismological us has already allowed us to understand that the last event has the same direction of the other faults. And if this is not the same, we’re still talking about a parallel.
This means that the movement has ended?
we don’t know, because you can calculate how much energy has been loaded during the geological process that we spoke of at the beginning. We do not know all the faults that there are, and how much resistance they have to the efforts or how they interact between them. The uncertainties from this point of view, are still many. The fact that the earthquake of 30 October has 'traced' the part of the two faults already active may not be negative. If he 'woke up' another fault would have been more worrying. This does not mean that the recent events may have caused the activation of another piece of the same fault or a contiguous.
