For decades it was thought that the seismic risk in the Strait of Messina had a single, large, culprit: a single, large fault capable of triggering the 1908 earthquake. But the reality, as often happens, seems more complicated. A study led by the National Institute of Geophysics and Volcanology (Ingv), recently published in the journal Tectonophysics in fact, it dismantles the old single fault model, in favor of a complex seismic system, formed by a mosaic of interconnected faults that runs throughout the Strait.
A clash between plates
The Strait of Messina is located at a meeting point between two large tectonic plates: the African one, which pushes north, and the Eurasian one, which resists and slides above it. The collision between the two plates deforms and breaks the earth’s crust, which moves along a series of active faults. It was believed that one of these, particularly large, crossed the Strait and was mainly responsible for the large seismic events that affected the area in the past.
New research changes this view today. The authors, who include researchers from INGV, CNR and several Italian universities, integrated seismological and geophysical data, analyzing over 2,400 earthquakes recorded between 1990 and 2019, of which they located the epicenter with precision techniques and also considering data recorded by monitoring systems placed on the seabed. The result is the most precise mapping ever made of the geological structure of the Strait of Messina, and of the potential seismic risks in the area.
A mosaic system
As we were saying, the work excludes the possibility that seismic activity in the strait area is dominated by a single, large fault that cuts the sea between Sicily and Calabria. And it indicates instead the presence of a complex system of interconnected faults, which extend both on land and under the sea and which move in a coordinated way, like a mosaic whose tiles slide and adapt to each other.
The seismic images acquired on the seabed revealed the presence of morphological scarps and dislocations in the recent sediments, unmistakable indications of constant geological activity, which until now had been masked by the action of strong currents and incessant underwater landslides. In short, the earth’s crust under the Strait is anything but stable.
The seismic risk
The new mapping also made it possible to identify two main layers of the Earth’s crust in which seismic activity is concentrated: a superficial one, between 6 and 20 km deep, where the most frequent earthquakes develop, and a second between 40 and 80 km. This double structure indicates that the deformation of the earth’s crust occurs on multiple levels and with different mechanisms: in the upper part, extensional forces dominate, which tend to lengthen and collapse the crust, while deeper down, compressive forces also appear, linked to the convergence between Africa and Europe.
Even if in the last 30 years the earthquakes in the area have always been of limited magnitude, the activity of the faults is consistent with that which triggered the great earthquake of 1908. This shows that the Strait, from a seismic point of view, is far from dead. And which will have to be studied with even greater precision in the future, to improve the current seismic risk prediction capabilities in an area that hosts several densely populated cities, is crossed annually by over 10 million passengers, and on which according to Government plans a bridge over three and a half kilometers long should be built.