By Mehdi Zare, professor at Earthquake Prediction Center, IIEES

Great earthquakes: is Istanbul the next candidate?

February 12, 2023 - 16:56

Major earthquakes on Monday morning, February 6, 2023, in southern Turkey and northern Syria, caused a lot of casualties and killed thousands of people in the central area.

Rescue forces are searching for the debris of buildings to find survivors who are facing severe winter cold, as well as power outages and water and panic caused by continuous aftershocks. 

The estimated fatalities say of about 50,000 to 70,000 people to be killed in Turkey and in the Syrian border area. The first earthquake with a magnitude of 7.8 occurred at 4:17 near Nurdagi- not far from the city of Gaziantep. 

The quake caused heavy damage in Syria, as well as in Iraq, Lebanon, Palestine, Egypt and Cyprus, and even parts of western Iran. Just nine hours after this earthquake, the second earthquake with a magnitude of 7.5 occurred on a different fault trend - with the east-west direction and due to triggering by the first earthquake. 

The first earthquake occurred at a depth of about 18 km in the eastern Anatolian fault system.

Historical earthquakes along the eastern Anatolian Fault EAFZ system are notable on November 29, 1114, with a magnitude of 7.8, March 28, 1513, with a magnitude of 7.4, and March 2, 1893, with a magnitude of 2. 7.1 and the earthquake of December 4, 1905; with a magnitude of 6.8. 

By February 6, 2023, there was an important seismic gap, especially at the southwestern end of this fault system, which ended on the morning of February 6.


Three main tectonic plates (Arabian, Anatolia / Eurasia, and African) are responsible for seismicity and tectonics in the Middle East and the region around Turkey. 

The collision of Arabian and Iran / Eurasian plates in the Iran region forms the strip of the Zagros mountain range and the Zagros drift with a length of approximately 1500 km, which passes through the whole west of Iran and extends to northeastern Iraq. 

The collision of Arabian and Eurasian plates also shortens the crust in Iran by about 3 cm per year. Along the eastern margin of the Mediterranean region, there is a complex interaction between the African, Arabian, and Eurasian plates. 

The Red Sea gap is a center of expansion between the African and Arabian plates with an opening rate of approximately 10 mm per year near its northern end, and 16 mm per year near its southern end. 

The extent of seismicity and the size of earthquakes and the gap process have been accompanied by the creation of a series of volcanic systems throughout the western Arabian peninsula. 

In the north, the Red Sea rift ends at the southern border of the Dead Sea Transform fault. This fault facilitates the movement of shifts between the African and Arabic sheets. 

Although the African sheet is moving in the west of the Dead Sea fault and the Arabian plate in its east, the Arabian plate moves a little faster, leading to the movement of the left-lateral slip along the border of this part of the sheet. 

The border of the sheet has historically been a hazardous region with the occurrence of earthquakes along the Dead Sea Transform fault in the densely populated area of the eastern Mediterranean. 

For example, in an earthquake in November 1759, it is estimated that between 2,000 and 20,000 people were killed. The northern end of the Dead Sea fault occurs in a complex tectonic area in southeastern Turkey. 

Where the collision of African and Arabian plates and the Anatolian block occurs. This includes the transition of the Anatolian block to the west, at a speed of approximately 25 mm per year compared to Eurasia, in order to adapt to the closure of the Mediterranean basin. 

The North Anatolian right-lateral fault system, in northern Turkey, facilitates much of the movement to the west between the Anatolian Bloc and the Eurasian plate. 

Between 1939 and 1999, a series of devastating earthquakes with a magnitude of more than M7.0 occurred along the North Anatolian fault system towards the west. The westernmost earthquake on August 17, 1999, was the M7.6 Izmit earthquake near the Sea of Marmara, which killed about 17,000 people.

Earthquake seismicity

There are three main fault zones in Turkyie called the Eastern Anatolian Fault (EAF), North Anatolian Fault (NAF), and Anatolian-Aegean subduction zone (AASZ). 

In the last two decades, EAF has been relatively quiet compared to NAF. A severe earthquake in 2003 in Bingol (MW = 6.3) occurred in the eastern intersection of EAF and NAF systems and towards the west, the Elazig earthquake with a magnitude of 6.8 occurred on January 24, 2020. 

The NAF system elongates about 1000 km between the Eurasian and Anatolian plates in northern Turkiye. The extension of this fault on the floor of the Marmara Sea in the south of Istanbul, with a slip of about 18 mm per year and the occurrence of historical earthquakes every 250 years, several M7 earthquakes are known. 

Thus, large earthquakes of M7 + have been delayed in this area, because this part of the fault has not been reactivated since the earthquakes of 1766 and 1754. 

The 2019 Istanbul-Siliuri M5.8 earthquake is important to determine its effect on the critical pressures of the Marmara Sea in the NAF system. 

The EAF Zone represents a plate border extending more than 700 km between the Arabian and Anatolian plates. 

At this border, relative movement with a slip rate of 6 to 10 mm per year occurs and has led to destructive earthquakes in eastern Turkiye. This EAFZ fault system is characterized by subdivisions with northeast-south-west and east-west directions, which are parallel to the general trend of the fault region. 

Fault mechanisms are mainly left-lateral. In two large earthquakes on February 6, 2023, first, an earthquake occurred in a northeast-southwest direction and then the second earthquake in the east-west direction. 

The proximity of the Euler pole to the rotation and displacement of the Arabian plate to the border of the Arabian-Anatolian plates leads to rapid changes in the velocity of the plate along the boundary, which is manifested by reducing the slip rate from the east (10 mm per year) to the west (about 1-4 mm per year). 

The EAF System shows heterogeneous seismic patterns with seismic absences (two of which ended in the February 6, 2023 earthquake) and local clusters. 

Seismicity study in this area determines the 150-year return period for magnitude 6.7-7.0 along the seismic sections in the east of the fault system. 

The western parts were apparently less seismic with the return periods of 250 to 700 years for Pazarcik (first earthquake 6 February 2023) and 414-917 years for Amanos for 7 to 7.4

By examining the statistics of Anatolian earthquakes, it is clear that such events can occur once a century. In 1939, an earthquake measuring 7.8 destroyed eastern Turkiye. 

This was the beginning of a sequence of domino earthquakes that occurred in the direction of the North Anatolian fault for more than 1,000 kilometers - almost from one end to the other - in a series of 12 very large earthquakes over 60 years. 

On the EAF system, on February 6, at 01:17:34 UTC, the first earthquake of magnitude 7.8 occurred in southeastern Turkiye, after which several aftershocks, including an aftershock with a magnitude of 6.7, occurred only 10 minutes later. 

The quakes occurred in the Gaziantep area with a population of more than 2 million. In the first earthquake, the southwestern part of EAFZ was broken for 180 km; from the surface to a depth of about 20 km (in a total seismogenic zone). 

It is possible that the remaining areas of the EAF zone will continue to be ruptured under critical stress through accumulated energy. The second earthquake occurred 9 hours later at 13:24 local time along the east-west fault, the end of which reaches the rupture zone in the morning of February 6, 2023, with a magnitude of 7.5.

Therefore, this second earthquake, which was located 100 km from the epicenter of the first earthquake, was not an aftershock and was the second independent earthquake.

Will the next one be a strong earthquake in Istanbul? One of the most important concerns in Turkiye is a severe earthquake along the northern Anatolian fault near Istanbul. 

After the two earthquakes of February 6, 2023, there has been a big debate in public opinion and in the Turkish media about whether the next important earthquake will be in Istanbul. Of course, if the two earthquakes of February 6, were to affect the faults in the Istanbul area, it should be said that it is unlikely that it will have a direct effect in the Istanbul area due to a distance of 700 km. 

The earthquake on the northern branch of the NAF system in the Marmara Sea, which passes through the city of Istanbul, has been very long. Three large historical earthquakes occurred in the North Anatolian fault zone in 474, 989, and 1766 with an estimated magnitude of about 7 to 7.5. 

Therefore, 257 years have passed since the last earthquake and an earthquake is expected in this area. It seems that with the situation in Turkiye after the earthquakes of February 6, 2023, this country, like most other middle east countries, is unfortunately not ready for severe earthquakes near densely populated urban areas.

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