The magnitude 7.3 earthquake on the Richter scale also left thousands injured on Sunday evening, November 12, 2017. This is the deadliest earthquake of the year in the world.


 

The magnitude 7.3 earthquake on the Richter scale also left thousands injured on Sunday evening, November 12, 2017. This is the deadliest earthquake of the year in the world.

The assessment of the magnitude 7.3 earthquake that struck northeastern Iraq and border areas in Iran and Turkey on Sunday night is getting worse. At least 421 people were killed and more than 7,000 blessings, according to a new count on Monday. Most of the victims were counted in Iran. This is the deadliest earthquake since the beginning of 2017 but not the most powerful, which remains that of 8 September in Mexico, a magnitude 8.2.

After initially placing the epicenter of the border earthquake, the US National Geological Institute (USGS) placed it on Monday - just like its Iranian counterpart - in Iran, close to the border, about fifty kilometers north of Sar Pol-e Zahab, the city most affected by the disaster, with more than 280 dead.

According to the Institute of Geophysics of the University of Tehran, tracking a follow-up of more than 150 seconds, including a duration greater than 4, with a maximum of 4.7 on the Richter scale. The public media have called for calm.

 

Earthquake in Iran: decryption of a geologist from UPMC



Responsible for the research directorate of UPMC, Bertrand Meyer is a geologist and professor at the Institute of Earth Sciences in Paris (iSTeP, CNRS / UPMC). He is interested in the deformation mechanisms of the continental lithosphere, the geology of earthquakes and knows Iran well, a field of exploration favored by many researchers of ISTeP. A magnitude 6.3 earthquake occurred in Iran on Tuesday, April 9, 2013. Are earthquakes predictable? Bertrand Meyer's answers.



An earthquake has just occurred in the region of Zagros in Iran, earthquakes are recurring in this country?



Bertrand Meyer: Zagros, mountain range at the front of the collision between Arabia and Eurasia, is a region of Iran characterized by a very important seismic activity. Earthquakes occur daily but not all are perceptible by humans. The earthquake of April 9, with a magnitude of 6.3, is an important earthquake for Zagros but it is a medium-sized earthquake. A magnitude of 6.3 corresponds to an average displacement of 40 to 50 centimeters on fault plane 10 kilometers long and 10 kilometers wide.

This earthquake occurred in a zone of convergence marked by the mountainous links of Zagros. Colliding with the Eurasian plate, the edge of the Arabic plate was shortened and thickened, forming the folds of Zagros (see photo). Some of these folds measure up to 100 km long, 10-20 km wide, 2 km high and are observable from space. These folds affect a series of sedimentary thick several kilometers with at its base a layer of salt, deposited in Cambrian about 550 million years ago. As the salt deforms very easily, the sedimentary cover is more easily shortened than the Precambrian basement under the salt layer.

It is likely that the reverse fault associated with this earthquake is responsible for wrinkle formation. However, it is difficult to reject the hypothesis of the reactivation of a basement fault, located under the salt layer, without further investigation.

 

What are the consequences of an earthquake on the Iranian landscape?



B.M: There are many faults in Iran: overlapping in the Alborz, staggering on the Iranian plateau and straddling the Zagros. In the case of the Zagros, a difficult question arises during each earthquake: did the earthquake occur on a fault affecting the sedimentary cover or on a deeper fault involving a shorter rigid base?

Given the sediment layer about 10 km thick and the hypocenter of the earthquake 10 km deep, it is difficult to conclude a priori. And this, especially since the break rarely reaches the surface of the soil in this region for such magnitudes.

Thanks to the seismic stations installed in the region, our Iranian colleagues will record the aftershocks that occur in the weeks following the main shock. Their distribution can bring us light on the area that has just deformed. A useful way to discriminate a fault that is in the sedimentary cover of a fault that affects the basement, would be to look at the deformation of the ground surface with the help of satellites. If the fault is close to the surface, there will be a larger amplitude deformation and wavelength than if the fault is deeper. We will therefore know more when the information transmitted by the satellites has been analyzed.

When an earthquake of magnitude 8 occurs, the landscape changes and there are offsets of the ground surface of up to ten meters. In the case of this earthquake of moderate magnitude, if the fault in question is in the sedimentary cover, the associated fold may have grown a few centimeters. Whether located in the sedimentary cover or in the basement, this earthquake is the most recent testimony of a geological history that has been going on for tens of millions of years. The Zagros will continue to shorten and the deformation will spread to the south. In a few million years, the Persian Gulf, whose depth is less than 100 meters, will surely have disappeared!



Is it possible to predict earthquakes?



B.M: The geological and paleoseismological studies informing us about the functioning of the faults that produce earthquakes at more or less regular intervals. They also tell us about the size of the earthquake that could occur in a region. Personally, I think earthquakes can never be predicted. Even if we succeed, no one could prevent the earthquake from occurring. It is therefore better to know the size of earthquakes that may occur in a given region to guard against their effects by building buildings that will withstand the jolts, than to expect to predict the very precise moment when they will strike. Seismic risk is also a function of gross domestic product (GDP): this is the reason why a moderate magnitude earthquake causes many more casualties in Armenia than in California or Japan.