The study conducted by the University of Catania, the Center for Ocean and Society - Institute of Geosciences of the University of Kiel in Germany and the INGV-Osservatorio Etneo of Catania was published in the prestigious international journal Earth-Science Reviews
The fault that more than 100 years ago caused the most serious seismic catastrophe in Europe, the Messina-Reggio di Calabria earthquake of 28 December 1908, has been discovered in the seabed between Sicily and Calabria.
A new study conducted on the seabed of the Strait of Messina and on the seismo-tectonics of the area - the result of an international collaboration between the Department of Biological, Geological and Environmental Sciences of the University of Catania (Giovanni Barreca and Carmelo Monaco), the Center for Ocean and Society- Institute of Geosciences of the University of Kiel in Germany (Felix Gross and Sebastian Krastel) and the Etna Observatory of the National Institute of Geophysics and Volcanology (Luciano Scarfì and Marco Aloisi) - unveils, for the first time, the location and geometric characteristics of the possible fault from which the devastating earthquake originated.
Title search “The Messina Strait: Seismotectonic and the Source of the 1908 Earthquake” has just been published in the prestigious international journal 'Earth-Science Reviews'.
A scientific answer that comes almost 113 years after that morning of 28 December 1908 when, at 5:20 local time, a devastating earthquake measuring XI on the Mercalli scale (estimated magnitude 7.1) caused destruction and death between Sicily and Calabria (Fig 1).
The telluric movement, which today is remembered in seismic catalogs as the most powerful ever recorded in Europe in the instrumental era, made the earth vibrate for more than 30 seconds and led to the complete destruction of the cities of Messina and Reggio Calabria and numerous other smaller towns causing the death of 100 thousand people (Fig. 2). The shaking was distinctly felt throughout southern Italy, in Montenegro, in Albania, but also in Greece and Malta and was followed, in less than 10 minutes, by a tidal wave (tsunami) which locally exceeded 10 meters height.
The wave hit the coasts of the Strait impetuous, adding devastation and death along the coastal areas already seriously damaged and where many frightened inhabitants had taken refuge (Fig. 3). Although at the dawn of instrumental seismology, the earthquake was recorded by numerous seismic stations around the world which placed its epicenter in the sea along the axis of the Strait of Messina.
Since that disastrous event, numerous scientific studies carried out by researchers from all over the world have tried to identify and characterize the tectonic structure responsible for the earthquake (the so-called fault or seismogenic source). However, the numerous geological models proposed, often conflicting, have fueled a heated debate in the scientific community over the years without however reaching a scientifically acceptable solution.
The study was mainly based on the interpretation of 35 high resolution seismic reflection profiles (a sort of ultrasound of the seabed) as well as on the analysis of seismological and geomorphological data examined in a multidisciplinary manner.
«The "ultrasound" of the seabed has made it possible to unequivocally identify a deep crack in the seabed of the Strait of Messina – explain the researchers -. The fault shows evidence of recent activity as it displaces the seabed with scarps up to 80 meters high (Fig. 4). Seismic analysis in a 3D environment and geomorphological studies on the ground then made it possible to follow the fault throughout its development, thus obtaining valuable information on its length, a fundamental parameter for estimating the maximum expected magnitude in the event of its reactivation but also a comparison with the 1908 event».
«The structure runs along the axis of the Strait and can be identified about 3 km from the coasts of Sicily (Fig. 5) – adds Barreca, research coordinator. At the latitude of Messina, the rift curves eastwards penetrating the Calabrian hinterland to then continue along the fluvial branch of the Catona torrent, a fluvial incision between Villa S. Giovanni to the north and Reggio Calabria to the south. The fault is inclined towards the east and reaches the maximum length of 34,5 km.
According to the length-magnitude relationships, the fault is capable of triggering earthquakes of magnitude 6.9, an energy very similar to that released during the 1908 earthquake. This data, together with the critical analysis of historical sources (for example the distribution of the and ground fracturing, the breaking of a telephone cable between Gallico and Gazzi) and the development of mathematical models of dislocation, suggests in fact that the tectonic structure identified is probably precisely the one which more than 100 years ago caused the most serious seismic disaster of the 900s».
The research also deals with the controversial issue of the mechanism at the origin of the separation taking place between Sicily and Calabria (about 3,5 mm per year), identifying the engine in the crustal depths where a further discontinuity is suspected of favoring the movement towards the east of an extensive block of crust including the area of the Strait and part of southern Calabria. This movement would occur under the effect of gravity and in an almost aseismic manner (ie not generating high-energy earthquakes) but would encourage the brittle rupture of some more superficial faults, including the cosismic rupture identified in the study, with the release of elastic energy.
The study therefore led to a critical review of the existing literature providing new constraints on the seismo-tectonics of the Strait of Messina, one of the areas with the highest seismic risk in Italy, and above all adds a significant element in the identification of the fault responsible for the earthquake of December 28, 1908. The updated seismo-tectonic model and the location of the possible fault responsible for the great earthquake could finally represent a useful basic tool for the safe design of future infrastructures in the area.
Link to scientific article: https://www.sciencedirect.com/science/article/abs/pii/S0012825221001860?via%3Dihub
Fig 1 - Map of the isoseisms (degree of damage) of the earthquake of 28 December 1908, drawn by G. Mercalli (1909). The epicentral isoseism reaches degree XI, defined as Catastrophic by Mercalli.
Fig. 2 - The first page of “il Telegrafo” with the news of the 1908 earthquake in Messina and Reggio Calabria (from the WEB). Victims at the port of Messina.
Fig 3 – Devastation at the port of Messina after the arrival of the tsunami wave (from the WEB).
Fig 4 – Seismic line (“ultrasound”) from Messina to Reggio Calabria showing the fault responsible for the earthquake (red line) which clearly deforms the sediments under the seabed and the seabed itself.
Fig 5 - The fault responsible for the 1908 earthquake mapped along the axis of the Strait of Messina and in southern Calabria.