Ten years after the L'Aquila earthquake, which deeply marked the lives of the citizens of Abruzzo and beyond, we went to see how a team of experts from the National Institute of Geophysics and Volcanology carries out a series of surveys at the base of the mountain slope del Morrone (Central Apennines) where, near the town of Roccacasale, an active fault emerges which is considered by the scientific community to be one of the main seismogenic sources in the Abruzzo Apennines.
Stefano Gori, an INGV researcher, has been engaged for months in geological activities on the ground, through excavations called "trenches", in order to discover the secrets of this "rock giant" and its fault.
What does the field work of INGV researchers in the trenches consist of?
The work consists in trying to clarify the activity of the faults in the last thousands of years, through the analysis of the walls of the trenches. Along these walls, in fact, it is possible to study the relationship between the movements of the fault and the sediments deposited along the slope of the mountain. Basically, every time a fault like that of Monte Morrone is activated, generating a high magnitude earthquake, the cosismic rupture propagates from the depth of the hypocenter of the earthquake up to the earth's surface, dislocating it and displacing what is along its trace. Obviously, this dislocation also affects the sediments that are deposited naturally along the mountain slope, as a product of the erosion of the limestone rocks that make up Monte Morrone. Therefore, these sediments allow the "geological recording" of past events defined, precisely, "paleo-events" of activation.
Why is it important to discover the history of the Monte Morrone fault?
The purpose of these studies, carried out in collaboration with the "Gabriele d'Annunzio" University of Chieti-Pescara and the University of Cassino and Southern Lazio, which are called "paleoseismological", is to investigate the recent geological history of movements of the fault to try to understand various fundamental elements such as, for example, how often the fault has been activated in the past millennia (called "recurrence time"), generating earthquakes of high magnitude (obviously, with uncertainties on the age of the order of a few centuries); how much time has passed since the last triggering event; the possibility of associating a strong historical earthquake known from Italian historical seismicity catalogs with the activation of the fault under study and, finally, what is the maximum expected magnitude of an earthquake generated by the studied fault. Obviously, this information is currently "uncertain" and cannot be used to predict future earthquakes, but it is nonetheless essential for having the most complete possible picture of the seismic hazard of the central Apennines.
What has been understood in recent years from the sequence of Central Italy (Amatrice, Norcia, Visso)?
The seismic sequence of 2016-2017 made it possible to verify the effectiveness of these geological studies conducted on active faults. In fact, investigations similar to those underway along the Monte Morrone fault were conducted just under twenty years ago along the Monte Vettore-Monte Bove fault. The results of these studies, combined with other types of geological investigations aimed at studying the activity of the fault in the last hundreds of thousands of years, had made it possible to define the Monte Vettore-Monte Bove fault as an active fault. Furthermore, the last activation event occurred before the last millennium and therefore potentially responsible for future seismic events of magnitude estimated around 6.5.
These studies were published about 13 years before the 2016 sequence but were only confirmed by the seismic sequence itself. In fact, it was actually caused by the activation of the Monte Vettore-Monte Bove fault and, in particular, the main shock of the sequence, which occurred on 30 October 2016, was of magnitude 6.5.
From a scientific point of view, the seismic sequence of 2016-2017 made it possible to verify that the geological approach used to study the Monte Vettore-Monte Bove fault is clearly useful. Its application to other active faults in the national territory is desirable, not only to improve in-depth knowledge of the territory but, above all, to plan the use of the territory itself in a more conscious way and to better carry out the activities aimed at reducing the risk seismic.