Mw6.0 earthquake shakes eastern Türkiye
A triggered event on the East Anatolian Fault between the 2020 Elazığ and 2023 Pazarcık earthquakes.
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On October 16, 2024 at 10:46 local time, a Mw6.0 earthquake struck eastern Türkiye, about 40 km east of the city of Malatya. The earthquake occurred at the eastern edge of the 2023 Kahramanmaraş ruptures, and is the largest event associated with the 2023 earthquakes since February 20, when a Mw6.3 earthquake occurred at the southwestern end of the rupture.
In the recent Mw6.0, shaking was felt up to 600 km away from the epicenter. The strongest shaking was felt close to the epicenter, reaching intensity VI-VII (strong to very strong). That is about the same level as was experienced at this location on February 6, 2023, but in this case was confined to a much smaller mountainous area, not including any major cities. Intensities at Malatya were ~V-VI. Overall, shaking lasted for about 30-40 seconds, according to testimonies reported to the EMSC.
According to the AFAD, the earthquake damaged three buildings and triggered a rockfall. There are no reports of deaths, although four people were rescued unharmed from a damaged building. Some injuries have been reported, largely due to people jumping out of windows. It is never recommended to jump out of a building from a high window. The chance that a felt earthquake will grow to be very large, combined with the chance that a modern building will collapse even in a large earthquake, is small. The chance of hitting the ground, on the other hand, is 100%. Even after escaping a collapsing building, falling debris outside the building and the ultimate collapse of the building structure itself still present serious hazards to someone lying injured on the ground nearby.
It is likely that many people are currently reliving some bad memories from the 2023 earthquake sequence, and so the instinct to exit a building as fast as possible is understandable. This is a significant issue with aftershocks: they are not just isolated earthquakes, and can take on importance larger than their direct effects.
Like the Mw7.8 earthquake on February 6, 2023, this earthquake occurred along the East Anatolian Fault Zone: a ~700-km-long left-lateral strike-slip fault that reaches from the Mediterranean coast in the southwest to its intersection with the North Anatolian Fault in the northeast. The civilizations that have come and gone in this history-filled region have all had to find ways to live with the erratic pulse of this dangerous plate-boundary fault system.
In 2023, the southwestern half of this fault slipped up to 8 m, in a rupture that caused the Mw7.8 Pazarcık earthquake. That earthquake was followed hours later by the Mw7.6 Elbistan earthquake produced by rupture of the Sürgü Fault to the northwest. The recent Mw6.0 earthquake (blue star on the figure below) occurred east of the ends of both of these ruptures.
This location, at the eastern end of the rupture, has been the subject of much study by the scientific community, mostly trying to figure out why the giant ruptures stopped here rather than continuing further to the northeast. Part of this can be explained by well-documented slip behavior of the eastern part of the East Anatolian Fault. In 2020, the Mw6.8 Elazığ earthquake was caused by rupture of the Pütürge segment, just to the northeast of today’s Mw6. That event, which killed 41 people and injured more than 1,600, also relieved some of the stress on the fault, making it more difficult for even a large and energetic rupture to propagate through this zone. Further east of the Elazığ rupture, careful observations of the fault have documented that it is creeping: moving a little bit every year, relieving stresses as they accumulate. So, it was fairly unlikely that the February 6 2023 earthquakes would be able to propagate into or beyond this zone.
However, questions remain about what exactly has happened in the zone between the 2020 Elazığ earthquake and the 2023 Pazarcık earthquake. This recent Mw6.0 earthquake occurred smack-dab within this gap.
First, we note that aftershocks of the February 6 earthquake extend past its mapped rupture.
The recent Mw6.0 occurred in this area: further to the northeast than the mapped surface rupture, but on the edge of the zone of 2023 aftershocks. Actually, the aftershocks start up again further to the northeast, but there is a notable gap at the location of the 2020 earthquake.
A study published in May 2023 (Karabulut et al., 2023) highlighted that there seems to be a change in fault dip in this region. They pointed to another study (Güvercin et al., 2022) that looked carefully at the aftershocks of the Elazığ earthquake, and found that the fault there dips to the northwest. In contrast, the northeastern end of the 2023 Pazarcık earthquake generally matched a more vertical fault (Barbot et al., 2023).
So, it seems likely that fault here consists of multiple segments, all relatively aligned at the surface, but with stepovers and changes in dip at depth.
This is particularly interesting, because the focal mechanism of the October 16 Mw6.0 earthquake indicates that the rupture occurred on a fault with a moderate northwesterly dip. For instance, the USGS solution indicates a dip of 43° to the northwest. Other networks provide a range of values, but all show that the northeast-southwest-striking plane dips distinctly to the northwest. That means that the earthquake better matches the orientation of the fault strand that slipped in the 2020 Elazığ earthquake. (We note that while the focal mechanism of the Elazığ earthquake does indicate a northwesterly dip, the fault plane for that event was still pretty steep — 70-80°).
The location of the Mw6.0 earthquake is consistent with this idea. When we roughly placed the quake on an along-fault section by Güvercin (2024), we found that it occurred quite close to the southwestern end of the Elazığ rupture. It’s not clear whether the earthquake falls within a slip patch of the 2020 earthquake, along an edge, or outside. Presumably some more detailed modeling than just slapping a star onto a published figure will illuminate this issue better.
So, how is this Mw6.0 related to the two previous large earthquakes in this area? In January, Toda and Stein put out a one-year earthquake forecast, taking into account both the 2020 and the 2023 earthquake sequences. We have previously referred to this forecast when discussing large aftershocks, and it has performed pretty well. When we place the recent Mw6.0 earthquake onto their map, we find that it is located in a region that was stressed by both events.
Here is a map of the Coulomb stress caused by the 2023 Kahramanmaraş earthquakes:
And here are maps showing the aftershocks of the 2020 Elazığ earthquake, and the predicted duration of aftershocks.
So, it does seem like both prior earthquakes made this Mw6.0 more likely to occur, by increasing stress on the frictionally locked fault.
The earthquake occurred in an area with an elevated risk of seismicity, according to the Toda and Stein 1-year forecast. They estimated that 1-3 M5+ events should occur over the one year period ending on December 1, 2024. This is the 3rd such event over this time period, so technically falls within the forecast, although it is unusually large.
Should this Mw6.0 count as an aftershock? That is really a matter of semantics. Yes, the Mw6.0 earthquake occurred after both earlier events. Yes, it was probably related to both. However, it stands out as unusual. If we were to count it as an aftershock of the 2020 earthquake, it would be unusually large and late. But, it is not on the same fault strand that ruptured in 2023. So, our initial preference is to consider this a likely triggered event; an earthquake that is part aftershock, and part its own thing.
If you scroll back up to Figure 7, one thing you’ll notice is that there is a substantial gap between the rupture areas in 2020 and 2023. One study of the fault here suggested that this 40 kilometer-long segment should count as a “seismic gap”: although it has produced aftershocks, there has not been enough slip on the fault to balance its neighboring segments (Barbot et al., 2023). That gap, they say, “raise[s] concern for the possibility of another Mw 6.8 earthquake to occur in this Pütürge segement of the East Anatolian Fault.”
Is this recent Mw6.0 earthquake that event? No. Although Mw6 and Mw6.8 may not seem that different, actually a Mw6.8 is much larger, releasing ~16 times more energy than a Mw6.0. This latest event released only ~6% of the energy of the larger possible earthquake proposed by Barbot et al.
Another way to compare that hypothetical Mw6.8 to the actual Mw6.0 is by looking at maps of estimated shaking. To do that, we would need a map of potential shaking in the hypothetical “seismic gap” — and fortunately, we created that map back in April 2023, in response to the Barbot et al. paper! When we put hypothetical future earthquakes into ground shaking models (we use the USGS ShakeMap tool), we are creating an earthquake scenario. The giant SCENARIO letters crossing the map at left are an indication that the earthquake has not actually happened - it is a tool for thinking about possible futures.
It is not at all clear that the remainder of this gap will ever slip in a Mw6.8 earthquake: if, as it appears, the fault system here is composed of multiple segments dipping in different directions, then perhaps we should expect smaller earthquakes breaking shorter fault segments in a patchwork of slip.
That being said, something similar to a Mw6.8 is not out of the question, and it is important to remember that the fault system here has already surprised us, especially with the second, triggered earthquake on February 6! It is also important to remember that we are seeing only a tiny part of the overall earthquake cycle, and that very large ruptures with the power to ignore the predictions of even the most high-impact publications might eventually occur.
OK, that’s our quick take on how this earthquake relates to previous, larger events. Now let’s zoom out and look at the fascinating geological setting of this earthquake, which represents a timeline much much longer than the earthquake cycle.
In the area of today’s earthquake, the East Anatolian Fault intersects the famous Euphrates River, the great stream that (along with the Tigris) brought forth agricultural civilization in the Fertile Crescent.
Near today’s earthquake, the river occupies a canyon more than 1 kilometer deep, which casually cuts through the two tall mountain ranges bracketing the fault. Today, much of this canyon is filled by a long, very narrow reservoir impounded by the incredibly picturesque Karakaya dam:
An interesting philosophical question arises: does the river cut the fault, or does the fault cut the river? Any philosophers in our audience are encouraged to argue ad infinitum about this in the comments.
A fascinating geological study of this area was published by Vladimir Trifonov and colleagues in 2018. This paper (a free PDF can be found here, from ResearchGate) presumably represents many years of field and laboratory work, aimed at understanding how environmental conditions have evolved in this area, over the last several million years.
We want to highlight this paper because it really has a bit of everything: fossil ancestral horses, fossil mollusks, seismically contorted strata, paleomagnetic polarities, tectonic terraces, radiometrically dated basalts, pollen counts, stratigraphic columns, and cross sections. This grab-bag of data reflects the challenge of studying the longer life of an area containing a highly active fault system.
At the human timescale, we see that fault movement causes earthquakes. But at longer timescales, they have even more dramatic impacts on the landscape. The surface geology shifts and changes. Rivers jump their banks, catchments capture or get captured by other catchments, mountains rise up or are eroded. At the same time, the climate is shifting its gears back and forth. The record of activity on faults is preserved in a patchwork of surface geology, most of which gets eroded away; what remains tends to be very difficult to date. Studies of long-term fault evolution rarely look at the fault itself, because the relevant deposits aren’t usually preserved along fault traces. Instead, a synoptic picture has to be built from laborious (but extremely rewarding - imagine taking a side trip to see Mount Nemrut on an off day) field studies of the whole area.
So, what did Trifonov et al. come up with for the East Anatolian Fault? One tectonic result is a reconstruction of the Euphrates River backward in time.
Here’s a set of maps that we modified from larger figures in Trifonov et al. At left is the Euphrates river crossing the East Anatolian Fault — as it might have looked, about one million years ago. Note that the topography is today’s topography, shifted backward by 13 kilometers. The actual pattern of small valleys, hills, and plains would have been different in detail. However, the big river can’t have moved that much.
At right is the present day, where the Euphrates takes a 13 kilometer leftward jog along the fault trace. After crossing the East Anatolian Fault, the Euphrates also has to cross the foothills of the Taurus Ridge, which were also apparently tectonically active during recent geological time.
Trifinov et al. approximately dated this offset of the Euphrates using their geological and paleontological data. The age constraint is a bit flexible because it is extremely hard to directly date landscape features like canyons.
A quick note - there is a simple mathematical conversion, easily done in the head, that can help transport us across geological time. If a fault moves at 1 kilometer per million years, then it is also, on average, moving at 1 millimeter per year (and vice versa). Thus, a left-lateral offset of 13 kilometers over 1 million years implies an average slip rate of 13 millimeters per year.
So, how do the observations of Trifinov compare to the present day? GPS and satellite radar measurements made repeatedly over time have indicated a modern slip rate of the East Anatolian Fault of between ~8-13 mm/yr. This is close enough to the slip rate of Trifonov et al. to suggest that the fault has been moving at a similar rate for at least 1 million years. The driving forces of this fault system — the relative motion of Arabia to the north, and ejection of Anatolia toward the west, are long-term effects.
Another interesting effect of strike-slip faulting across a displaced river channel is that the river actually gets longer over time. The Euphrates has apparently grown about 13 kilometers longer due to this fault offset!
Today’s magnitude 6.0 earthquake probably had a maximum slip of about 10 centimeters, with the slip happening only on a deeper part of the fault. This isn’t much, and the Euphrates probably didn’t actually get much longer today.
However, the river is constantly growing. In fact, the Euphrates follows a remarkable portion of the fault: one that slips both steadily as slow creep, and also quickly during large earthquakes. Satellite imagery of the region can track the movement of the crust on either side of the fault. Those observations indicate that some of that motion happens as aseismic creep.
The figures below show relative motion across the fault for different time periods. The top two panels show motion during the time between earthquakes. Blue on one side of the fault vs. orange on the other side indicates a small amount of creep.
The third panel is a little tricky - it shows the surface slip that happened during the earthquake, but the color scale now goes up to 30 cm in each direction. So satellites can tell us that the Euphrates river grew about 50-60 cm longer over a period of a few minutes during 2020 - pretty nifty if you ask us.
The bottom panel shows the months after the earthquake. The surface fault slipped quietly again, slowly lengthening the Euphrates by a few millimeters per year.
What will happen as this fault continues to move? Well, a river can grow for a long time, but not forever. After some time, it is likely that the offset will block the flow of the river, or align a new lower drainage, making it more efficient for the river to choose a new path, abandoning its previous bed and quickly changing its length once again — probably some millions of years in the future.
References:
Barbot, S., Luo, H., Wang, T., Hamiel, Y., Piatibratova, O., Javed, M.T., Braitenberg, C. and Gurbuz, G., 2023. Slip distribution of the February 6, 2023 Mw 7.8 and Mw 7.6, Kahramanmaraş, Turkey earthquake sequence in the East Anatolian fault zone. Seismica, 2(3). https://doi.org/10.26443/seismica.v2i3.502
Cakir, Z., Doğan, U., Akoğlu, A.M., Ergintav, S., Özarpacı, S., Özdemir, A., Nozadkhalil, T., Çakir, N., Zabcı, C., Erkoç, M.H. and Basmenji, M., 2023. Arrest of the Mw 6.8 January 24, 2020 Elaziğ (Turkey) earthquake by shallow fault creep. Earth and Planetary Science Letters, 608, p.118085. https://doi.org/10.1016/j.epsl.2023.118085
Güvercin, S. E., 2024. 2023 Earthquake Doublet in Türkiye Reveals the Complexities of the East Anatolian Fault Zone: Insights from Aftershock Patterns and Moment Tensor Solutions. Seismological Research Letters, 95(2A), pp.664-679. https://doi.org/10.1785/0220230317
Güvercin, S.E., Karabulut, H., Konca, A.Ö., Doğan, U. and Ergintav, S., 2022. Active seismotectonics of the East Anatolian fault. Geophysical Journal International, 230(1), pp.50-69. https://doi.org/10.1093/gji/ggac045
Hubbard, J. and Bradley, K., 2024. Mw5 aftershock occurs near epicenter of 2023 M7.8 Turkey-Syria earthquake. Earthquake Insights, https://doi.org/10.62481/fad55236
Hubbard, J. and Bradley, K., 2023. There is a 40 km seismic gap on the East Anatolian Fault near Malatya. What would a M6.8 earthquake there look like? Earthquake Insights, https://doi.org/10.62481/a9c9ca0a
Karabulut, H., Güvercin, S.E., Hollingsworth, J. and Konca, A.Ö., 2023. Long silence on the East Anatolian Fault Zone (Southern Turkey) ends with devastating double earthquakes (6 February 2023) over a seismic gap: implications for the seismic potential in the Eastern Mediterranean region. Journal of the Geological Society, 180(3), pp.jgs2023-021. https://doi.org/10.1144/jgs2023-021
Melgar, D., Taymaz, T., Ganas, A., Crowell, B.W., Öcalan, T., Kahraman, M., Tsironi, V., Yolsal-Çevikbil, S., Valkaniotis, S., Irmak, T.S. and Eken, T., 2023. Sub-and super-shear ruptures during the 2023 Mw 7.8 and Mw 7.6 earthquake doublet in SE Türkiye. http://dx.doi.org/10.26443/seismica.v2i3.387
Ren, C., Wang, Z., Taymaz, T., Hu, N., Luo, H., Zhao, Z., Yue, H., Song, X., Shen, Z., Xu, H. and Geng, J., 2024. Supershear triggering and cascading fault ruptures of the 2023 Kahramanmaraş, Türkiye, earthquake doublet. Science, 383(6680), pp.305-311. https://doi.org/10.1126/science.adi1519
Toda, S. and Stein, R.S., 2024. The role of stress transfer in rupture nucleation and inhibition in the 2023 Kahramanmaraş, Türkiye, sequence, and a one‐year earthquake forecast. Seismological Research Letters, 95(2A), pp.596-606. https://doi.org/10.1785/0220230252
Trifonov, V.G., Ҫelik, H., Simakova, A.N., Bachmanov, D.M., Frolov, P.D., Trikhunkov, Y.I., Tesakov, A.S., Titov, V.M., Lebedev, V.A., Ozherelyev, D.V. and Latyshev, A.V., 2018. Pliocene–Early Pleistocene history of the Euphrates valley applied to Late Cenozoic environment of the northern Arabian Plate and its surrounding, eastern Turkey. Quaternary International, 493, pp.137-165. https://doi.org/10.1016/j.quaint.2018.06.009