The eastern flank of Etna undergoes a continuous “sliding” towards the east. And one of the “guiding tracks” of the movement is the Pernicana fault system which represents the northern limit of the unstable portion of the volcano.
This was revealed by a research entitled “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- Etneo Observatory (Salvatore Alparone, Alessandro Bonforte, Flavio Cannavò, Andrea Ursino), from the University of Bologna (Eleonora Rivalta) and 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), that is repeating earthquakes. , even years later, 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 that allows to reconstruct in detail the dynamics of the faults 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 soil deformation data, which are acquired by GPS antennas distributed along the flanks of the volcano and measure the variations in the shape of the volcano, it was possible to subdivide the Pernicana fault in different portions that show different behaviors in terms of seismicity and soil deformation – explain the researchers -. In particular, it was noted that the western portion of the fault, close to the summit eruptive centers, shows a notable “segmentation” in depth. The central portion, on the other hand, is characterized by a single clear fault surface, whose seismicity is mainly associated with multiplets. The eastern portion of the fault, on the other hand, is almost asismic, practically showing no seismicity ».
“The study of the recurrence times of multiplets showed a lack of periodicity and a low degree of regularity in terms of the temporal occurrence of earthquakes – add the researchers -, this suggests that 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 occurs instead along the San Andreas fault following the relative displacement between the tectonic plates), but rather from triggering phenomena of an episodic nature, linked for example to the upwelling of magmas.
The ascent pressurizes the volcano’s feeding system with consequent thrust on the eastern flank and sliding, as macroscopically occurred, for example, during the 2002-2003 eruption ».
“The study – the researchers conclude – shows how the identification of multiplet earthquakes and their integration with soil deformation measurements can help investigate the dynamics and structure of faults in detail, not only on Etna but in any system of active faults in both volcanic and tectonic areas ».