The study by a team of researchers from the universities of Catania and Bologna, from the INGV-Osservatorio Etneo and from the GFZ German Research Center for Geosciences in Potsdam, was published in the journal "Communications Earth & Environment" of the Nature group
The eastern flank of Etna undergoes a continuous "slip" towards the east.
One of the "rails that guide" the movement is the Pernicana fault system which represents the northern limit of the unstable portion of the volcano.
This is revealed by a research titled “Repeating earthquakes and ground deformation reveal the structure and triggering mechanisms of the Pernicana fault, Mt. Etna” published in the journal 'Communications Earth & Environment' of the Nature group.
The study was developed by a team of researchers from the University of Catania (Andrea Cannata, Adriana Iozzia, Stefano Gresta), from the INGV-Osservatorio Etneo (Salvatore Alparone, Alessandro Bonforte, Flavio Cannavò, Andrea Ursino), from the Bologna (Eleonora Rivalta) and of the GFZ German Research Center for Geosciences in Potsdam (Simone Cesca).
The team of researchers studied the seismicity generated by the fault system over the course of 20 years (from 2000 to 2019) and discovered how the Pernicana generates a large number of "multiplets" (also called repeating earthquakes), i.e. earthquakes that repeat , even after many years, identical to themselves in terms of location, source mechanism and seismogram.
A feature common to very active fault systems such as the San Andreas fault in California which allows the dynamics of the faults to be reconstructed in detail and, therefore, to understand how, when and by how much they move.
«Through the study of multiplets and thanks to the integration of seismic data with ground deformation data, which are acquired by GPS antennas distributed along the sides of the volcano and measure the variations in the shape of the volcano, it was possible to divide the Pernicana fault into different portions showing different behaviors in terms of seismicity and ground deformation – explain the researchers -. In particular, it has been noted that the western portion of the fault, close to the summit eruptive centres, shows considerable depth "segmentation". The central portion, on the other hand, is characterized by a single clear fault surface, the seismicity of which is mainly associated with multiplets. The eastern portion of the fault, on the other hand, is almost aseismic, showing practically no seismicity.".
«The study of the recurrence times of the multiplets has shown a lack of periodicity and a low degree of regularity in terms of the temporal occurrence of the earthquakes – add the researchers -, this suggests how the movement of the fault, and therefore the sliding of the eastern flank of Etna, does not derive from a constant and permanent stress (as instead occurs along the San Andreas fault following the relative displacement between the tectonic plates), but rather by triggering phenomena of an episodic nature, linked for example to the ascent of magmas.
The ascent pressurizes the feeding system of the volcano with consequent thrust on the eastern flank and sliding, as macroscopically occurred, for example, during the eruption of 2002-2003».
"I study – conclude the researchers - shows how the identification of multiple earthquakes and their integration with ground deformation measurements can help to investigate fault dynamics and structure in detail, not only on Etna but in any active fault system in both volcanic and tectonic areas».
Link to the scientific article
Figure 1- In the photo you can see the cut just made during an earthquake.
Also, on the right you can see a low wall that no longer exists in photo 2.
Figure 2- The photo shows the restoration of the road surface and the retracing of the centerline.
Furthermore, the dislocation that took place near the wall can be seen, clearly visible in photo 1.
