On April 22, shortly after 23 pm, a strong earthquake that occurred in Bosnia Herzegovina was distinctly felt in our country. To understand what happened and the characteristics of this seismic event, we interviewed Rita Di Giovambattista, Director of the INGV Earthquake Department.
What characteristics did the earthquake have?
The main event had a local magnitude ML 6 and took place around 10 kilometers deep, with its epicenter about 60 km south of Mostar.
After 2 minutes from the seismic event it is possible to have a first automatic estimate of the position of the epicenter and of the magnitude of the earthquake based on the data sent by the INGV seismic stations
This event was followed by aftershocks, the strongest to date of magnitude ML 5.1.
What type of mechanism, from a seismic point of view, distinguishes the area?
The mechanism of the seismicity of the affected area is due to the northward convergence of the African plate towards the Eurasian plate.
In the past, the same region has been affected by other events of significant magnitude: the earthquake of September 5, 1996 with a magnitude of 5.8 about 15 kilometers southwest of today's epicenter and that of February 14, 1927 with a magnitude of 6.0 about 15 kilometers to the north . The most devastating seismic event that hit Bosnia and Herzegovina was the 6.4 magnitude Banja Luka earthquake, which occurred in October 1969.
The northward convergence of the African plate with respect to the Eurasian plate makes the Mediterranean region seismically active. Where are the highest seismicity rates found?
The highest seismicity rates are found along the Hellenic subduction zone of southern Greece, along the northern Anatolian fault zone, western Turkey, and the Calabrian subduction zone of southern Italy.
According to the official estimates of the European Community (Pesaresi et al, 2017) the global exposure of the population and the built area to natural hazards has increased in the last 40 years and earthquakes are the main cause of exposure for the population.
In particular, in Europe more than one hundred and seventy million people are exposed to a significant danger of earthquakes and Italy is one of the regions with the highest seismic risk together with Turkey, Romania, Greece and other states of the southern Balkans.
The quake of April 22 was also distinctly felt in Italy. Where exactly?
The earthquake was felt distinctly on the Italian territory, particularly on the Adriatic coast and in the central-southern regions. These resentments are confirmed by the preliminary map of the effects of the earthquake obtained from over 6000 questionnaires collected on the INGV website. The questionnaires are filled in by citizens who, in this way, can give valuable information on how the earthquake was perceived by them.
From the data collected, we have estimated that the macro-seismic impact in our country has reached the fourth degree of the Mercalli Scale.
Why was it so strongly felt in Italy?
It was also strongly felt in Italy because a magnitude 6 earthquake is capable of releasing enough energy to be felt up to hundreds of kilometres. There have been hundreds of reports on the Italian Adriatic side: the shock is part of the eastern edge of the Adriatic where the Adriatic lithosphere, i.e. the crust plus the earth's mantle, descends under the Dinarides, a mountain range that crosses all of former Yugoslavia, as well as descends below the Apennines.
The Tsunami Alert Center of the National Institute of Geophysics and Volcanology (CAT – INGV), was set up in response to the need to provide Italy with a control system for tsunamis potentially harmful to its coasts. Has an alarm been issued for the earthquake of April 22?
The CAT-INGV operates as a Tsunami Service Provider certified by the ICG / NEAMTWS (Intergovernmental Coordination Group for the Tsunami Early Warning and Mitigation System in the North-Eastern Atlantic, the Mediterranean and connected seas) which is an integral part of the global warning and Tsunami Risk Mitigation, established and coordinated by the Intergovernmental Oceanographic Commission (IOC) of UNESCO.
On the occasion of the strong earthquake that occurred on April 22, the CAT issued an information message in just 6 minutes, therefore not an alert, in which it communicated that a significant impact on the territory would have been unlikely due to the tsunami possibly generated by the event seismic.
Finally, INGV participates in SHARE, a project that aims to overcome political boundaries, unknown to earthquakes. What exactly is it about?
SHARE (Seismic Hazard Harmonization in Europe), has as its objective the elaboration of a seismic hazard map extended to the whole of Community Europe and to North Africa through the sharing of data and methodologies between nations in which seismological disciplines have reached a different level of development.
Projects like this serve to highlight that seismic hazard calculations cannot only consider earthquakes that occur in our area but must also include those generated in surrounding seismic areas, as in the case of the recent event in Bosnia and Herzegovina. As we have seen, there can be resentments even at great distances and, in some cases, events can generate potentially dangerous tsunamis for our coasts.