With thousands dead and injured and many buildings and infrastructure destroyed, the 7.8 magnitude earthquake that struck Turkey and Syria early Monday morning It was one of the most devastating in recent years.
A confluence of factors triggered the disaster.
The combination of the intensity of the earthquake, its depth, its geographical location, the type of fault that generated it, its length or the power of the aftershocks magnified the tragedy.
Here we tell you what factors multiplied the destructive capacity of the earthquake.
1. Magnitude 7.8
The first quake, registered in the early hours of Monday near Gaziantep (Turkey), when people were sleeping, was of magnitude 7.8, which is considered “major”.
The magnitude quantifies “the energy that is released in the earthquake” and, globally, “there are usually about two earthquakes of a similar magnitude per year, although most occur under the ocean or in unpopulated areas,” explains Stephen Hicks , seismologist at University College London (UCL).
The largest magnitude recorded since earthquakes have been measured was the one that took place in Chile in 1960, which reached 9.5.
As the Chilean geophysicist Cristian Farías points out, “the magnitude is as if you go to a concert and the band is playing with a fixed volume. Obviously it is the volume that they set and it is one, just as the earthquake only has one magnitude.”
However, depending on where you are in the room, “you are going to have a different experience of the concert. The same thing happens with the intensity. If you are in different places with respect to where the earthquake occurred, you are going to feel different effects,” adds the Professor at the Catholic University of Temuco.
This is where a new factor comes into play: intensity.
2. IX degree
The effect of an earthquake on the earth’s surface is what we call the intensity, which is measured with what is known as the “Mercalli seismological scale”.
This scale “estimates the intensity of an earthquake based on things like how much the ground moved, with what acceleration it moved, if there are buildings that fell or not… the level of destruction,” explains Farías.
The scale is measured in Roman numerals and goes from I to XII.
In the case of the first earthquake on Monday, several points in Turkey, around the cities of Osmaniye, Kahramanmaras, Adiyaman or Malatya, registered an intensity IX, which is considered “very destructive” and it implies, for example, a severe destruction of buildings and collapses, as unfortunately it has been possible to observe.
3. Powerful subsequent earthquake
Although earthquakes are usually followed by smaller aftershocks, the second quake felt on Monday was of a very similar magnitude, 7.5.
This is something that only usually happens in 10% of cases, explains Stephen Hicks, who recalls that it is impossible to know when or where the next earthquake will occur.
In fact, Monday’s second quake occurred on a different branch of the Eastern Anatolian Fault, which runs from the southwest to the northeast.
“This highlights the complexity of trying to make predictions, because you may not have known the flaw existed until something finally happened with it,” says the UCL professor.
The fragile state in which many buildings had been left contributed to new landslides with the next earthquake, increasing the tragedy.
4. 18 kilometers deep
The earthquake was, scientists agree, very superficial since it occurred only 18 kilometers deep in the earth’s crust.
What happened then is that “the vibrations that came out of the earthquake did not lose enough energy before reaching the surface, and that caused extreme shaking in the area that many buildings, especially traditional Middle Eastern ones, were not prepared to withstand.” Hicks says.
5. 150 kilometer failure
The size of the fault, 150 kilometers long by 25 kilometers thick, was another factor that contributed to the destruction.
“One tends to think that the longer the fault is, the wider it is also going to be. [el radio afectado]but in this case we had a very, very long and very thin one, which means that all the energy was really concentrated in the superficial parts, and that is always very complicated for any construction”, explains Cristian Farías.
6. Transcurrent failure (strike-slip)
The type of fault that was generated in the earthquake in Turkey and Syria, known as strike-slip faulting, also contributed to the destruction.
To have large intensities, Farías points out, “you don’t necessarily need an earthquake with a very large magnitude.”
Indeed, the one on Monday, measuring 7.8, is not so big compared to other large earthquakes that have occurred in the world, such as the one in Japan in 2011, measuring 9; that of Alaska of 1964, of 9.2; or that of Chile in 1960, of 9.5.
“Since the scale that measures them is logarithmic, they are much larger earthquakes, but they do not always have the intensity in some areas that this one did generate,” adds the Chilean specialist.
The manner in which this quake occurred, with transient faulting, added to its devastation.
To explain this type of failure, Hicks proposes to imagine a paper that is torn: “it is a horizontal movement, like what you do when tearing a paper. Imagine tearing that paper 400 kilometers, that tear produces vibrations that are felt very far away. from the epicenter in a very intense way”.
Farias uses the simile of bread dough: “to break a bread dough, basically, we take a piece and move it here and there, right? The same thing happens with the crust, only you have large pieces of rock and if you move one relative to the other, you will generate this rupture within the crust,” he explains.
The problem, the geophysicist points out, is that “not only does the earthquake start superficially, but the entire movement is superficial, reaching almost even to the ground. And, then, if someone lives nearby, as happened in Turkey, the acceleration “It produces on the ground is very large. The effect you feel is as if you received all the energy of the waves, but immediately, almost like being in the front row at a heavy metal concert.”
7. Type of constructions
And here, the experts agree, the second part of the destruction arrives: the capacity of the buildings to resist the earthquakes.
While in countries like Japan or Chile the construction regulations are very strict due to the recurrence of strong earthquakes, it is possible that in Turkey and Syria many buildings did not conform to the regulations.
“In the images that have come down to us from the earthquake, you can see buildings that are completely on the ground and, next to them, others that have remained standing. This happens because, surely, those that are standing were built considering the norm, contemplating all the scenarios, and not the others”, ventures Farías.
There is a constant challenge in countries that have major earthquakes to understand these scenarios and prepare for them “because we pay the cost with lives.”
“Disasters are not natural,” concludes Farías, “they depend on how one prepares for the threat.”
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BBC-NEWS-SRC: https://www.bbc.com/mundo/noticias-internacional-64561968, IMPORTING DATE: 2023-02-07 21:40:07
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