Earthquake: What seismic threat is facing Istanbul, located near a very active fault ?

Jacques Malavieille est directeur de recherches au CNRS, à Montpellier. DR – DR

Ce sujet a fait l’objet d’une conférence par un directeur de recherches du CNRS, invité par le centre d’études et de recherches Benjamin-Bardy.

Jacques Malavieille, CNRS research director in Montpellier, gave a conference on the oceanographic campaign in the Sea of ​​Marmara (near Turkey). The oceans cover 75% of the Earth's surface. Their average depth is around 4,000 meters, which explains why a very small surface area of ​​the ocean floor has been explored to date.

However, knowledge of them is fundamental to understanding the dynamics of our planet. The means of exploration and study are numerous, but too costly to be applied systematically. However, the location of geological structures responsible for certain natural disasters is not limited to continental areas.

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In the Sea of ​​Marmara

Very large fractures cross the oceans and their study is complex because direct observation is almost impossible. In 2002, an oceanographic campaign took place in the Sea of ​​Marmara. Its aim was to better understand the seismic risk in the vicinity of Istanbul, a vast metropolis of 10 million inhabitants.

For the first time, scientists aboard the Atalante (a French ship from Ifremer) studied one of the largest faults on the planet, the North Anatolian Fault (NAF). Under the effect of the “punching” of Anatolia (Turkey) by the Arabian plate which is moving up towards the north, the “Anatolian block” is expelled towards the Aegean domain (Aegean Sea) to the east.

Un robot sous-marine

Lateral movement along the highly active FNA generates very large, destructive earthquakes. One of its segments, which has so far been little studied because it cuts into the Earth's crust at the bottom of the Sea of ​​Marmara, threatens Istanbul. The resources deployed during the Marmarascarps campaign, including the use of an underwater robot piloted from the ship (the Victor 6000), enabled a detailed study of the seabed at a depth of more than 1,000 meters.

At sea, precise mapping of the rupture zone associated with the latest large earthquakes shows that the loaded (under stress) fault segment is shorter than previously estimated. The magnitude of the future earthquake likely to affect Istanbul has therefore been revised downwards. However, it remains impossible to predict when this earthquake will occur and what its impact on the city will be.

To conclude the conference, a possible cause for the Flood, a catastrophe recounted in the Bible, is discussed in light of modern scientific data. Jacques Malavieille's presentation raised many questions from the audience.

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