Moroccan Earthquake Occurs Outside High Activity Zone, Yet Aftershocks Anticipated, Says Expert

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One French expert cautioned that the devastating earthquake in Morocco, which claimed over 2,000 lives, did not strike the region with the highest seismic activity. However, he issued a warning about the likelihood of aftershocks.

Philippe Vernant, a specialist in active tectonics, particularly in Morocco, at the University of Montpellier, addressed questions from AFP regarding the catastrophic earthquake.

Was the earthquake in Morocco unexpected?
Morocco is one of those nations where the question isn’t whether earthquakes will occur.

In 1960, the Agadir earthquake, with a magnitude of 5.7, annihilated the entire city and resulted in nearly 15,000 casualties. More recently, there was the Al Hoceima earthquake in 2004, with a magnitude of 6.4, farther out in the Mediterranean.

If we delve further into history, there were earthquakes in the 18th century, likely around magnitude 7 in the Fez region.

The recent earthquake’s epicenter was not located in the most seismically active region of Morocco. However, the High Atlas mountains are present, and this type of earthquake contributes to the uplift of the High Atlas range.

Was the Moroccan earthquake similar to the one in Turkey in February?
In Turkey, there was horizontal movement because Turkey is shifting westward, moving toward Greece. This resulted in horizontal sliding of the tectonic plates.

In contrast, in Morocco, we observe more of a convergence between Africa and Eurasia or Iberia, the Spanish part, along with overlapping faults. Nevertheless, we are still dealing with plate boundaries.

What accounts for the intensity of the Moroccan earthquake?
We need to consider the magnitude of the earthquake, which is estimated to be around 6.8 or 6.9, a fairly strong level.

This roughly corresponds to an average displacement along the fault line of approximately one meter in just a few seconds, over several kilometers. Naturally, this has a profound impact on the region.

Additionally, there is the issue of depth. Initially, it was estimated to be around 25-30 kilometers, but it seems to be shallower, closer to 10 kilometers. The closer the earthquake is to the surface, the greater its impact.

A similar situation occurred in France in 2019 in the Teil region in southern Ardeche. It was considered a “minor” earthquake, but because it occurred at a depth of just one kilometer, it had significant effects.

Should we anticipate aftershocks in Morocco?
Aftershocks are inevitable.

Even if they are less intense, they can result in the collapse of buildings already weakened by the initial earthquake.

Traditionally, we tend to believe that aftershocks decrease in intensity. However, in Turkey, one earthquake triggered another. The initial rupture can lead to the activation of another fault through a cascade effect, which is why there is sometimes a risk of a more powerful earthquake following the initial one.

Is it feasible to predict such events?
Regrettably, we cannot make predictions.

We attempt to estimate recurrence intervals based on the various magnitudes of earthquakes, but behavior can be erratic, with two strong earthquakes occurring within a short timeframe followed by an extended period of quietude.

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