A major earthquake struck southern Turkey early on Monday, causing extensive damage and killing thousands there and in neighboring Syria. Rescue workers have been searching the rubble of buildings for survivors, who face bitterly cold winter temperatures, as well as electricity and water outages—and the terror of continuing aftershocks.
The magnitude 7.8 temblor struck close to Nurdağı—not far from city of Gaziantep—at 4:17 A.M. local time, according to the U.S. Geological Survey. It was also felt in Lebanon, Israel and Cyprus. The quake was followed by a magnitude 7.5 aftershock several hours later, as well as numerous smaller aftershocks. (The earthquake magnitude scale is logarithmic, so an earthquake with a magnitude of 7.0 is 10 times larger than one with a magnitude of 6.0. The former also releases 32 times as much energy as the latter.)
Monday’s quake involved a fault rupture that was relatively shallow—about 18 kilometers (11 miles) below Earth’s surface—making surface movements more intense. According to the New York Times, this earthquake caused the collapse of nearly 3,000 buildings in Turkey and killed more than 3,000 people across that country and Syria. [Editor’s Note (2/13/23): The death toll has risen to more than 35,000 people.] The toll of those killed and injured is expected to rise because of the region’s high population density, particularly among the number of Syrian refugees who often live in makeshift or otherwise less robust structures.
To learn more about this notoriously seismically active region and why this earthquake was so damaging, Scientific American spoke with seismologist Ross Stein, CEO of the catastrophe modeling company Temblor.
[An edited transcript of the interview follows.]
Why is Turkey such a seismically active area?
Turkey is squeezed by a giant tectonic vise. The Arabian subcontinent is shoving northward, and it’s pushing Turkey north against basically a fixed boundary of northern Europe. And so what happens is Turkey is squeezed outward to the west, where it spills into the Mediterranean and ultimately gets shoved underneath Crete in a subduction zone like we see off Japan.
How common are earthquakes of this size and intensity in Turkey?
They’re rare—that’s the short answer. They are probably on the order of a once-a-century kind of event. We did have a magnitude 7.8 earthquake in 1939. That was the beginning of the most spectacular falling-domino sequence of earthquakes the world has ever known. That ruptured the North Anatolian Fault over 1,000 kilometers—almost from one end to the other—in a series of 12 very large earthquakes over 60 years. It’s a slo-mo car crash, where one earthquake is triggering the next and the next and the next. Although we know that the San Andreas and other faults of this kind are capable of something like that, this is the clearest, simplest example we’ve known.
What makes these stronger quakes so rare?
In the kind of weird math of earthquakes, every time you bounce up one magnitude unit, you get one tenth of the occurrence rate. So as you go to larger and larger sizes, they become less and less frequent. There are arguments about that. Some argue that you can identify the maximum size of an earthquake that characterizes a fault. But I don’t think the data show that. In 100 years, if we have 20 magnitude 7’s, we should have two magnitudes 8’s. Roughly speaking, that’s what we see.
And can they get still larger? Nobody knows. The hubris of the seismic community is to argue that we can divine how large an earthquake can be [on a given fault]. On the East Anatolian Fault [where the recent earthquake occurred], lots of researchers had kind of pegged the maximum magnitude in the neighborhood of 7.4.
This earthquake ruptured over a fairly long stretch, about 400 kilometers, and was followed by a magnitude 7.5 aftershock. Can you talk about these and any other interesting aspects of this quake?
So one of the things that we do, that Temblor does and a lot of scientists do, is try to calculate how one earthquake changes the conditions for failure around it. We call this “Coulomb stress triggering.” And we made a calculation last night, which we sent out to our clients, where we showed that this earthquake should light up parts of the East Anatolian Fault, farther to the north and to the south. And we had a magnitude 7.5 early this morning [ET] in, basically, that blowtorch zone. So it was kind of similar to what we saw in the falling-domino sequence along the North Anatolian Fault—which means this may not be over. Earthquakes are in a kind of chain reaction; they converse by the transfer of stress. One earthquake might drop the stress on the section that ruptured, but it transfers it to other sections. Aftershocks tell us that story. Aftershocks don’t just occur where their rupture took place. They occur around it over fairly large distances.
Why was this earthquake particularly damaging?
The number one factor is building quality. It just trumps everything else. Building quality is controlled by a building code and the enforcement of that code. Turkey went through the terrible 1999 Izmit earthquake, which killed [more than 15,000] people, so Turkey had modern building codes within a few years of that earthquake. So then you say, “Well, given that, why do buildings fail? Are these buildings older than 20 years ago? Or were the buildings built in a manner that was not properly reinforced?”
After that Izmit earthquake in 1999, I was there. We were inspecting a factory. You build a strong building with reinforced concrete, which is the standard building material the world over. What you do is: You have rebar—you have these steel rods that are inside the columns and beams. And you concentrate the strength and the density of those at any corners, any junctions, because that’s where the earthquake stress is going to be concentrated.
So we were inside this failed manufacturing plant, and I could see there was a big crack at one of these joints—big enough that I could get my hand in to see how many reinforcing rods were in there. I put my hand in, and I pulled out a hunk of Styrofoam. The world would be a safer place if concrete was translucent. This is the problem: it’s too easy to cheat.
I don’t know if the buildings that fell [in the recent quake] are older buildings or poorer buildings, so I’m not accusing anybody of anything. But this is the problem worldwide, not just in Turkey.
What other things would you like people to be aware of with the risk of earthquakes?
I think it’s a reminder. I think what’s happened over the past five years is: people willed themselves to believe that earthquakes don’t occur anymore, and it’s now just floods and wildfires. So that’s definitely the view in California. It’s kind of willful blindness. It’s understandable, because it’s been a long time in California [since a major earthquake]. So this is a reminder of what can happen in a very San Andreas–like setting, that big earthquakes do happen. This is our future. And the difference between a relatively harmless earthquake and a disaster is how well we build our buildings and how well we prepare.
If people want to do one thing—and it costs $1—to make themselves safer in earthquake country, put an international orange whistle on your keychain. And the reason is: if you’re trapped in a building, no one is ever going to try to dig you out unless they know you’re alive. You can’t yell for very long before you use up all your moisture, nor can you be heard very far. With this whistle, you can be really loud for a really long time.