“It’s a rarity to have such big earthquakes in this area”

5 mins

Pain and shock in Morocco. A powerful earthquake occurred on Friday September 8 in the High Atlas mountain range, in Morocco, causing hundreds of victims, destroying numerous buildings and forcing residents to flee their homes.

The National Center for Scientific and Technical Research (CNRST) based in Rabat indicated that the earthquake had a magnitude of 7 degrees on the Richter scale and that its epicenter was located in the province of Al-Haouz, in southwest of the city of Marrakech.

This is the strongest earthquake to hit the kingdom to date. A “surprising” phenomenon, according to Florent Brenguier, seismologist at the Institute of Earth Sciences at the University of Grenoble, because the area where the epicenter is located is not located “at the interface between two tectonic plates” .

France 24: In Morocco, the seismic risk is rather concentrated in the north of the country. How then can we explain such a powerful earthquake in the center? ?

Florent Brenguier: Firstly, you should know that all of Morocco and generally the entire Mediterranean area is likely to suffer major earthquakes. However, it is actually around the border of the African and European plates in the north of the country that the majority of earthquakes are concentrated, particularly around the Strait of Gibraltar.

On the other hand, there is the entire Atlas zone which, despite everything, is a risk zone. Even though earthquakes are less frequent, their magnitude can be significant. The most striking example is the Agadir earthquake in 1960 which caused the death of 12,000 people and almost destroyed the entire city.

There are significant faults in this area which have developed over geological time, that is to say thousands, tens, even hundreds of thousands of years. However, it is a rarity to have such large earthquakes in an area that is not located at the interface between tectonic plates.

This is what happened last February in Turkiye and Syria…

Yes this earthquake took place at the border between the Anatolian plate and the Arabian plate. We knew that in this area, there could be very large earthquakes because we are at the border of two major plates. There in the case of Morocco, it is true that it is surprising because it is rare to have such large earthquakes inside the plates.

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The magnitude of the earthquake in Morocco is 7 on the Richter scale, against 7.8 in Turkey and Syria. What does this represent in terms of the difference in power generated ?

The best representation is undoubtedly to evoke the length of the fault: around 30 kilometers for the earthquake in Morocco, it was 300 kilometers in Turkey. It’s ten times smaller. The energy sent underground is therefore much lower and the earthquake more localized. If we had had an equivalent earthquake in Morocco, we can imagine that a large part of the city of Marrakech would have been destroyed.

After this earthquake, the inhabitants are now worried about possible aftershocks. Is this the next danger that awaits Moroccans ?

You should know that the intensity of aftershocks decreases over time. There has already been one of 4.5 on the Richter scale so we now have less chance of having big aftershocks.

On the other hand, it was realized that the initial shock caused by an earthquake could trigger another earthquake. In this case, it is no longer a replica. This is what happened in Turkiye. There were two earthquakes with a magnitude of 7.8 for the first and 7.5 for the second. This is a phenomenon that has already been observed in Japan and California.

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This possibility now exists in Morocco. It is not impossible that there will be a second big earthquake which is not necessarily on this fault. It could be a little further north or a little further south. This most often occurs within hours or days of an earthquake, but it can also be weeks or even months later.

Why can’t we predict earthquakes? ?

For the moment, what we are able to do is to determine the seismic zones. This was the case in this area where magnitude 4 earthquakes have been recorded in recent years, which have been felt by the population. So, we are able to map areas where there is potentially a risk.

However, the real difficulty is knowing what is the maximum magnitude that these potential earthquakes can reach. Here is the problem. Moreover, if we have identified a major fault, where there could be a great earthquake, we cannot predict when the next great earthquake will occur.

Scientists have not yet found reliable warning signs that allow us to detect an anomaly. But this is a field of research that is evolving and perhaps in the future, we will be able to find signs that will be used to anticipate an earthquake.