The Anatolian and Arabian plates meet in southern Turkey. In an interview, the geophysicist Krawczyk explains how such violent earthquakes occur and why they are so difficult to predict.
tagesschau.de: What exactly happened in southern Turkey?
Charlotte Krawczyk: We have two plates there that are moving horizontally past each other, the Anatolian and the Arabian plates. They’ve been doing this for a long time and quite regularly, at around two centimeters a year.
Such strong earthquakes occur when part of this movement is not directly converted into movement and dissipated, but when the plates get stuck and tension is built up as a result. At some point, a threshold value is reached and when this is exceeded, the big event occurs, where the pent-up tension is then discharged.
Geophysicist Charlotte Krawczyk works on earthquakes at the German Research Center for Geosciences in Potsdam. Her main research areas include seismic methods and technical developments in applied geophysics.
tagesschau.de: It has been relatively quiet at precisely this interface in recent years. What is currently happening?
Krawczyk: In fact, it was quiet there for almost 900 years – and scientifically too quiet for geodynamics. Nothing happened there for a long time. This is an area where many small earthquakes occur again and again. And last night the whole thing probably got triggered and then escalated. After the big event, we were able to measure many aftershocks, some with large magnitudes of four to five.
Later, another event occurred with a magnitude of about 7.4 – that is, the plates have not yet come to rest there. But we can’t say when that happened or why it happened that way. We have not observed any precursor phenomena in this case.
There were numerous earthquakes in the Turkish-Syrian border area. The main event took place at a depth of 10 kilometers.
tagesschau.de: How can you even measure what’s happening down there?
Krawczyk: The magnitudes and evaluations are what the GEOFON network in the Geoforschungszentrum in Potsdam measures worldwide every day and makes available online at any time. We have an international earthquake catalog and many sensors that are set up worldwide and constantly provide us with data. If there is a big event, it can be localized.
And then we not only look at the automatically detected signal, but also manually rework it. To be absolutely sure: Where is the location and above all at what depth did the event probably take place? In this case from last night, the depth is given as ten to 15 kilometers below the earth’s surface.
tagesschau.de: How does depth affect earthquake severity?
Krawczyk: The flatter and denser it is under the surface of the earth, the closer it takes place to our feet, the faster it is with us, of course, and the more of this pent-up energy is then converted into destructive energy, so that buildings, infrastructures, for example, collapse be destroyed or something like that. If an earthquake of magnitude 7.7 had occurred 50 to 100 kilometers below the earth’s surface, for example, we would have felt the effects, but not nearly as severely.
In this case, there is also the fact that the plates slide past each other horizontally. We’re not too far from the surface of the earth and that causes the surface of the earth to vibrate, which then leads to these damage cases.
tagesschau24 2:00 p.m., 6.2.2023
tagesschau.de: How do you have to imagine these vibrations?
Krawczyk: There is a great rift, that is, what we describe as our solid earth is being torn open over a great length. If I tear something open, then of course I have to move it somewhere. That is, for one, I have the propagation of the crack itself. On the other hand, the rock is also torn down there, so to speak, and thus set in motion. As a result, the earth’s body also begins to vibrate.
And these seismic waves propagate through the Earth’s body, and that’s why we can measure them here in Potsdam, for example. If that energy wasn’t propagating, we wouldn’t even know this earthquake happened. This means that the earth begins to vibrate. We can measure all of this worldwide. And maybe to give an example of what happened with this earthquake: It happened at 1:15 am local time. Five minutes later the propagation of this earthquake wave was in Potsdam. And in Potsdam, after five minutes, the earth’s surface rose by three millimeters due to this strong earthquake.
tagesschau.de: But we didn’t really notice these three millimeters here, did we?
Krawczyk: No, we don’t notice that. Above all, it always makes a huge difference: does it happen very abruptly and quickly or does it just pass through us as a long-wave event and we don’t even notice it? And that’s such a phenomenon because we’re about 2,000 to 3,000 kilometers away from where it happened.
tagesschau.de: Is it even possible to detect earthquakes in advance? With measuring instruments?
Krawczyk: We all dream of it and are researching hard to one day be able to better indicate the probability of earthquakes. This helps us, for example, to invest in research into early warning systems in order to get to know precursor phenomena at all. What you always have to do is to study these precursor phenomena for a certain region over a longer period of time in order to derive what is special there and how an earthquake would spread there.
tagesschau.de: What are the precursor criteria that can exist there?
Krawczyk: There may be areas where, for example, a seismic crisis occurs and we would have something like a whole lot of small earthquakes. They accumulate over time, become more and more frequent and you can observe them. This could indicate, for example, that there is an event going on that might lead to a stronger event.
But just this kind of phenomena, so: When is it really an indicator of underground behavior? Or is it just natural behavior? You can only really measure and model this in order to make a prediction if you observe it over a long period of time and then collect this knowledge specifically for an area.
tagesschau.de: You said that the dream of many researchers could come true. What has to happen for this?
Krawczyk: I think what has already developed a lot is that we can measure globally and worldwide. However, we also have measurement gaps in many areas. It’s not like we’ve covered everything nice and evenly like we do in this case. In Turkey there are many regional networks that also measure and do not have to be fed into this global system. This is good for the time being in order to do this type of monitoring regionally and also really country-related.
But for our measurement gaps, we need something else. For example, what’s very strong on the front lines of research right now is that we’re using fiber optic cables as seismological sensors. If we can also query this better over large distances, then we can close many measurement gaps. And this also helps us to assess whether a phenomenon can be classified as critical, precursor or normal.
tagesschau.de: In the case of this earthquake, was there any precedent that they say could have been a sign?
Krawczyk: We can’t answer that. Perhaps the closer measuring instruments on site will be able to answer this question at some point. At the moment, of course, something completely different is in the foreground on site. With the network that we have available worldwide, we cannot make this statement. Nevertheless, we examined our data because we would like to know that, of course, but we have no indication that there were any precursor phenomena.