The earth shakes - whose fault is it?
Ramblings of a geologist after the Turkey/Syria earthquake of February 2023
And again a major earthquake fills the pages of the newspapers because of the many thousands deaths. Again no geologist, geophysicist or seismologist is surprised that there was such a strong earthquake in that area. Insiders are well aware of the most dangerous seismic areas in the world. The Anatolian Peninsula, mostly occupied by Turkey, is one of them, on a par with California and Mexico, Japan, Chile and Peru, to give a few examples of states on plate margins. By now we know well the different plates into which the Earth's lithosphere is divided and where they interact releasing large amounts of energy. So why so many deaths?
Of course, the history of man is far longer than that of geology. Great civilizations of the past built without regard to seismic or volcanic risk. They could not have known that. But we do know, and the buildings we saw being filmed as they collapsed are not ancient. It is possible to build earthquake-resistant structures that can withstand such strong earthquakes. It is challenging and expensive but it is possible. You can also secure pre-existing buildings but that is also challenging and expensive. Why is it not done? Why doesn't anyone bother before the carnage happens? Geology can tell us exactly where it needs to be done. But while when NASA or ESA ask for billion-dollar investments for space exploration something gets done, if the geological surveys of nations exposed to such dangerous seismogenic faults asked for investments to secure homes, what would happen?
Immediately I am reminded of the wiretap between two builders who were happy that there was a destructive earthquake in central Italy in 2006: they were rubbing their hands because they were going to make big money from the reconstruction! Is this the key takeaway? Is reconstruction more profitable than securing before an eventual disaster? Same dynamic as wars? The country that bombed then invests in reconstruction. Prevention is less profitable and is also less visible, it brings fewer votes than reconstruction after disaster.
So why listen to geologists bringing bad luck? Besides, geology is not even a real science, according to Sheldon from The Big Bang Theory. But if you also watch the Young Sheldon series you will understand that Sheldon's is just spitefulness toward a geology-loving young girl who rejected him as a child. No serious astrophysicist would dream of saying that geology is not a science. It is just younger, having developed its basic theory in the 1960s, Plate Tectonics. It satisfactorily frames the phenomena occurring on the planet, especially on its surface. It explains very well why earthquakes occur, which is why no geologist is surprised by them: they are a natural phenomenon, they are inevitable, that's how the Earth works. After all, if you think of a ball of magma immersed in space at -273°C whose surface is solidifying rapidly, you can imagine that this surface is not a single block but is broken up into many parts (the plates) and that these parts interacting with each other will make some mess…
Specifically, a large fraction of the Anatolian Peninsula is part of a plate of its own, which is compressed between the northward-moving African and Arabian plates and the immense Eurasian plate pushing southward. These movements force the Anatolian plate to slide westward by 2 mm per year along the two fault zones bordering it to the north and southeast (North Anatolian Fault Zone "NAFZ" and East Anatolian Fault Zone "EAFZ").
Here is a tectonic diagram from the article "Comparative PGA-driven probabilistic seismic hazard assessment (PSHA) of Turkey with a Bayesian perspective" by Nas et al. (2020) from Journal of Seismology (click here for the link). After all, just look at Turkey on Google Maps and select the "relief" option to see these two fault zones clearly from the surface morphology.
The earthquake in question was generated along the EAFZ near the Turkey-Syria border. These are fault zones similar to the better known San Andreas in California. The blocks they separate move laterally relative to each other: for example, if we stand to one side relative to the North Anatolian Fault (NAFZ) we would see the other block move to the right. If we do the same thing with the EAFZ we would instead see the other block shift to the left. In fact, they are called "right-lateral strike-slip fault" and "left-lateral strike-slip fault," respectively.
If you put a concrete block in a press and squeeze, when at some point the block will break it will do so mainly along two planes oriented less than 45° from the direction in which the press is squeezing. One will be right-moving like the North Anatolian fault, the other will be left-moving like the East Anatolian fault (which if you look at the map continues northeast with the NEAFZ fault zone). In short, these are two main, conjugate and antithetical (from opposite motion) slip surfaces that accommodate the deformation undergone by the concrete block in the press. They intersect with each other outlining a wedge that moves inward into the broken concrete block, while the rest of the block is pushed sideways, expanding with the two parts moving outward. Between Turkey and Syria it is the Arabian plate that is the wedge while the Anatolian plate is one of the sides moving laterally, "expanding."
Taking the wedge back to planetary scales and the press action time to geologic scales, imagine the enormous forces involved and the extremely long deformation times. In the press we would see the concrete block break suddenly, but in nature everything is extremely slower. Fault zones form bit by bit. Even the cracks in the concrete block if we looked at them in slow motion: a little crack here, another little crack there, and slowly a slip plane forms. The same happens between plates. The little cracks here and there are the individual earthquakes that happen as the fault plane carries out its movement. How could we predict when each one will happen? At the scale of a plate, the forces at play and the volumes of rock displaced are enormous, and there are those who think that man can trigger earthquakes by his drilling or by pumping gas underground. An earthquake is no one’s “fault” (pun intended). This is how our planet evolves. If we want to avoid damage, we can only study it properly, understand it, and build accordingly. We have the technologies to do that. But we won't and we will continue to count the dead. But be very careful of those who shift the blame to scientists who did not predict, to wells that have been drilled, or to other collateral activities. The deaths are not from the earthquake but from the collapsing buildings, remember that well....