Fatal double whammy: On February 6, 2023, two severe earthquakes shook southeast Turkey – they are the strongest ever documented in this region. The tremors were felt even in Baghdad, in Cairo and throughout the Middle East. The cause of these strong earthquakes was the East Anatolian fault, a plate boundary that had previously remained seismically quiet for a suspiciously long time. Why did the current earthquakes occur? And why is Turkey particularly at risk of earthquakes?
Many people in Turkey will not forget February 6, 2023 in a hurry. Because on that day, severe earthquakes shook the south-east of the country twice in a row. At around 2:00 a.m. the first earthquake with a magnitude of 7.8 occurred near the city of Gaziantep, followed at noon of the same day by a second strong earthquake with a magnitude of 7.5. As a result, numerous buildings collapsed, several thousand people died in the rubble, and many more are still buried and missing. But how did this catastrophe come about?
Stuck between several earth plates
Turkey is located in a tectonic high-risk zone – a kind of ejection seat of the tectonic plates. In this region, several tectonic plates collide. The biggest players are the African plate in the southwest and the Eurasian plate in the north. Both collide in slow motion as Africa drifts north. A smaller fragment of the African Plate, the Arabian Plate, is moving northward at a particularly rapid rate, forcing the Anatolian Plate between it and the Eurasian continent.
This has consequences: the Anatolian plate is being pushed out of the side of these pincers and is therefore shifting westwards by two to three centimeters per year. As a result, two large fracture zones, so-called transform faults, are created in Turkey, where the plate boundaries shift laterally against each other.
Two break zones and a triple knot
In the north, the North Anatolian Fault stretches from the Iranian border to Istanbul. This active fracture zone was responsible for a strong earthquake in the northern Turkish city of Izmit in 1999, among other things. In addition, this fracture zone poses an acute danger for the metropolis of Istanbul. In 2019, seismologists determined that enough stress had built up underground to trigger a magnitude 7.1 to 7.4 earthquake. As a result, a strong earthquake can also occur there at any time.
In the south-east of Turkey is the East Anatolian fault zone, where the Anatolian and Arabian plates are shifting against each other at around 1.4 centimeters per year. This fracture zone is the plate boundary where the severe earthquakes have just occurred. Their epicenters are even at a triple junction, because that is where the East Anatolian fault meets the foothills of the Dead Sea fault zone and the Cyprus Arc, a plate boundary running in the Mediterranean Sea.
Long pent-up tensions
The problem with this: The plate boundaries in Turkey do not slide past each other smoothly, but get caught again and again. As a result, the movement of the tectonic plates slows down and enormous tension builds up in the depths of the faults. At some point, the pent-up forces are so strong that the rock breaks and the plates jerkily move into a new position – an earthquake occurs. The earth’s crust ruptures deep down. The longer the tectonic plates have been blocked and the more stress has accumulated, the more severe the jerk and the longer the resulting rift.
This was also the reason for the unusually strong tremors of February 6, 2023: Unlike in northern Turkey, the East Anatolian fault has been unusually quiet over the past 100 years – there has been hardly any seismic activity. The last major earthquake in this area occurred on December 4, 1905 and had a magnitude of 6.8. “So the entire zone has built up tension over this long period of time, and it was only a matter of time before an earthquake would occur,” explain experts from the GeoForschungsZentrum Potsdam (GFZ).
The two strong earthquakes of February 6, 2023
That’s exactly what happened. In the early morning of February 6, without much warning or noticeable clusters of preceding weaker earthquakes, the tension in the East Anatolian fault erupted. First, an earthquake of magnitude 7.7 to 7.8 occurred near the city of Gaziantep. According to initial estimates by seismologists, this earthquake ruptured the fault over a length of at least 180 kilometers and down to a depth of 20 kilometers.
With a magnitude of 7.8, this earthquake was the strongest ever documented in this region. For Turkey as a whole, it was the strongest earthquake since 1939. At that time, 30,000 people died in an earthquake of similar magnitude. The tremors were still felt in Istanbul, more than 80 kilometers away, in Baghdad and in Cairo, Egypt. In the Lebanese cities of Beirut and Tripoli, the ground was still shaking so badly that some people fled outside for fear of their homes collapsing.
At noon of the same day, a second strong earthquake with a magnitude of 7.5 followed about 100 kilometers north on an adjacent line of the fault. “This was strong enough to be considered a separate tremor, but it is likely to have been triggered by the first tremor,” said Jenny Jenkins, an earthquake researcher at Durham University in England.
Why were the earthquakes so devastating?
The energy released by the tremors was more than double that of the strongest historic earthquake on this fault zone, according to seismologist Jenkins. This alone explains why the earthquake caused such severe damage.
But there is something else: The source of the earthquake was only around eleven kilometers deep – that is relatively shallow for a strong earthquake. As a result, the earthquake waves lost little energy on their way to the earth’s surface and generated correspondingly strong surface waves there. As a result, the subsoil in Gaziantep and the surrounding areas moved particularly violently and led to the collapse of the buildings.
Source: USGS, GFZ German Research Center for Geosciences