TEHRAN - The occurrence of earthquakes on February 6, 2023, Mw7.8 and Mw7.5 in southern Turkey and northern Syria, on the northwestern border of the Arabian plate and at the point of collision with the Anatolian block (Eurasian plate), and the occurrence of the earthquake on 12 November 2017 in Sarpole Zahab in the basement of Folded Zagros belt in Iran, Mw7.3 has raised the important question of where and when the next major earthquakes may occur on this border and around the Arabian Plate.

Are the next strong earthquakes with the same magnitudes possible in the coming years?

The opening of the Red Sea is associated with the convergence of the Arabian and Eurasian plates. 

At the leading edge of the Arabian Plate, the folded Zagros Mountains shortening in the last ten thousand years at a rate of 20 mm per year has resulted in major episodes of coastal uplift, the last of which was 1700 BC. 

In the transform, Jordan rift, which bounds the Arabian plate in the west, a return period of about 1600 years has been reported for ML 5.5 events. 

The paleomagnetic record for the last 3.2 million years shows that the average rate of extension for the Red Sea is about 20 mm/yr. 

There is evidence that hydrothermal activity in the Red Sea is pulsatile with a return period of 2000 years, indicating discontinuous expansion. 

The Holocene neotectonic record of the Zagros, Jordan Rift, and the Red Sea is the product of complex plate interactions and the accumulation and release of strain in the crust along the plate margin. 

But they also reflect the storage and release of elastic strain energy in the Arabian plate, from which parallels the major deformation periods in the three deformation zones and the apparent discrepancy between the seismic moment predicted by the plate kinematics and that recorded in the Zagros. 

Any in-plane deformation, if detected geodetically, helps in seismic hazard assessment.

At the beginning of 2023, about 180 million people live on the Arabian Plate, and about half of them live on the borders of this plate (about 90 million people), on the other hand, about 20 million people live in Iran - in the Zagros Mountains - and 10 million in Turkey (southeast of Anatolia) and about 15 million in Egypt and Sudan, adjacent to the Arabian Plate boundaries. 

Therefore, a population of over 135 million people lives on or near the borders of the Arabian Peninsula. 

Earthquake risk for cities near these borders, such as Beirut, Damascus, Aleppo, Gaziantep, Diyarbakir, Shiraz, Ahvaz, Bushehr, Bandar Abbas, Kuwait City, Doha, Dubai, Manama, Medina, Jeddah, Sanaa, Aden, and Cairo, are exposed to the most possible damages caused by the next earthquakes are on the boundaries of the Arabian plate.

On the other hand, the Arabian Plate currently contains 48% of the world's oil reserves and 43% of the world's natural gas reserves. 

The Arabian plate experienced approximately 570 million years of uninterrupted sedimentation, an ideal environment for hydrocarbon generation.

We try to answer this important question: What are the next most important possibilities for the rupture of the faults in the borders, and the future large earthquake events to be destructive for the cities on the edge of this plate?

The earthquakes occurred on February 6, 2023, in Turkey along the active Eastern Anatolian fault. 

The active Eastern Anatolian fault system is about 700 km long and defines the northern border of the Arabian plate with the Eurasian (Anatolian) plate. 

The friction between the blocks produced by this movement releases energy in the form of earthquakes. Faults can rupture as often as once every few decades to hundreds of years, such as the ruptures on 6 February 2023 in the East Anatolian Fault system. 

Today's movements in and around the Arabian plate include a wide range of tectonic processes including subduction, continental collision, seafloor spreading, intra-plate magmatism, and continental transform faulting. 

Therefore, the amount of slip and the relative directions of the plate movement, and the possible deformation within the plate are very important to assess the seismic hazard in the boundaries of the Arabian plate and the areas within it. 

The internal strain at the scale of the plate surface is very low and stable at the inner boundaries of the plate, which are more typical of coherent rigid motion in the Arabian plate. Of course, on a smaller scale, there are few displacements.

Geological Formation of the Arabian plate

The opening of the Red Sea and the Gulf of Aden to the south, compression in Turkey and Iran in the north, and the presence of transform faults on the flanks determine the general tectonic situation around the Arabian plate.

The region near the triple junction between the Arabian, Eurasian/Anatolian, and African plates have often been the focus of studies of continental deformation behavior and interseismic deformation. 

Several large earthquakes have occurred on the border of the Arabian Plate, including the 7.1 magnitude earthquake in 2011 in eastern Turkey.

The Arabian Plate consists mostly of the Arabian Peninsula. It extends from the west to the Sinai Peninsula and the Red Sea and from the north to the Levant, in the east, with the Indo-Australian Plate in the Owen Fracture Zone in the Indian Ocean, in the west with the Dead Sea Transform Fault (DST) boundary. 

Towards the south, the Arabian plate is constrained with a divergent boundary with the African plate called the Red Sea Rift. 

Towards the north, the Arabian plate has a convergent boundary with the Anatolian plate and the Eurasian plate, including the Eastern Anatolian fault, the fold and thrust belt of Zagros and Makran.

The opening of the Red Sea began at the end of the Eocene about 34 million years ago, and the separation of Africa and Arabia occurred approximately 25 million years ago in the Oligocene, and since then the Arabian plate has been moving towards the Eurasian plate. 

The collision of the Arabian and Eurasian plates has formed the Zagros mountains of Iran and northern Iraq. 

Because the Arabian plate and the Eurasian plate collide, some cities such as the cities of southwestern Iran, northern Iraq, and southeastern Turkey (which are located on the edge of the Arabian plate) are very seismic.

The Arabian plate is surrounded by seismically active tectonic boundaries, including the Zagros-Bitlis fault in the northwest and north, the East Anatolian fault in the northwest, the Aqaba-Dead Sea fault (ADSF) in the west and northwest, the divergent boundaries of the Red Sea and the Gulf of Aden in the west. The vast majority of earthquakes occur within the borders of the Arabian plate.

The boundaries of the Arabian plate are approximately 2600 km in the northeast and 3000 km in the east, and the thickness of the plate is approximately 40 km.

The Iranian Plateau is located in the north of the Arabian plate along a wide area of deformation, which is a part of the Alpine-Himalayan orogenic belt between the Arabian plate in the southwest and the Eurasian plate in the northeast. 

The Strait of Hormuz region in the south of Iran has the highest seismic activity in the region and its formation is related to the continuation of the convergent movement between the Arabian plate and the central continental plate of Iran. 

The Zagros Mountain belt is formed in the collision zone between the Arabian and Eurasian plates, and this active convergence has led to a lot of seismicity in this region. 

Many and frequent earthquakes occur mainly 2 to 15 km deep in the seismogenic layer. The rate of shortening is faster in the southeast than in the northwest, and this is due to the counterclockwise rotation of the Arabian sheet.

Seismicity

The entire region has a significant seismic risk. The Arabian plate is surrounded by areas of high seismicity. 

The calculation of this seismicity is of great importance for the assessment of seismic hazard and risk, seismic zoning, and land use. Plate boundary friction has been responsible for very destructive earthquakes in the past. 

In 1138 and 13 August 1822, earthquakes with a magnitude of 7 to 7.5 caused the destruction and casualties of several thousand people in the Syrian city of Aleppo.

On the Zagros Main Recent Fault a dextral strike-slip mechanism is representative, i.e in the Silakhor earthquake of 23 January 1909, with a magnitude of 7.4 on the Doroud fault, and In the folded Zagros belt, the Sarpole Zahab earthquake of 12 November 2017, on the Zahab basement fault, Mw7.3, is the largest recorded events in the Zagros belt.

The destructive earthquakes of 6 February 2023 occurred in the south of Turkey with magnitudes of 7.8 and 7.5 due to the rupture in the northwestern border of the Arabian plate along the eastern Anatolian fault zone.

Assessing the probability of the next important earthquake in the Arabian plate

In order to predict and evaluate the next important earthquakes, the theory of plate displacement and stress accumulation on a locked fault is generally implied, along with the observations of past earthquakes on that fault and the current speed of plate movement. 

Based on this model, in the epicentral zone of the 6 February 2023 earthquakes, the return period of an earthquake with an M7.5 is about 370 years, and for an Mw7.8 is about 1700 years. 

Such return time is required for enough Stress to build up on the fault in order to cause another major earthquake. 

Due to the dispersion of geodetic stations, it was not possible to determine the slip rate of different parts of the Eastern Anatolian fault system, but some GPS data monitored since the 1990s, are available. 

With these data, the slip velocities on different parts of the fault can be calculated at least for the last decades.

Large earthquakes may also occur in more stable areas of the continental crust. Significant amounts of elastic strain can be released on geologic structures far from plate boundary faults. Plate boundaries are where the vast majority of Earth's seismic activity takes place. 

Intraplate earthquakes have different spatial and temporal patterns than plate boundaries. These earthquakes occur in areas where the level of tectonic stress is negligible and they occur when the accumulation of local tectonic stress in active faults reaches the threshold of failure. 

As a result, earthquakes can occur in areas with no previous seismic history and no surface evidence for strain accumulation. 

Thus, the seismic hazard of such earthquakes is likely to be greater than that indicated by past earthquakes, current seismicity, or tectonic strain rates.

In Syria and the adjacent lands in the north of the Arabian Plate, the neotectonic structure of the region is affected by displacements along the parts of the Dead Sea transform fault. 

Taurus thrust fault (Bitlis) continues in the east and then the main Zagros thrust. The shortening of the Palmyra-Anti-Lebanon thrust belt has separated the Aleppo block from the main part of the Arabian plate. The Dead Sea fault is active in the area of the Sham fault.

The countries of Kuwait, Bahrain, Qatar, United Arab Emirates, Oman, Yemen, Saudi Arabia, Syria, Jordan, and Iraq are located on the Arabian plate.

The Red Sea is opening at a rate of approximately 10 mm per year, and the Gulf of Aden is believed to be a growing rift. The westward opening occurs at a rate of approximately 3 mm per year. 

As the Red Sea continues to open, the Arabian Plate finally collides with Eurasia, and the Zagros Mountains are formed. 

These mountain ranges are shortened by 9±3 mm per year in the southeast and 5±3 mm per year in the northwest. 

The Dead Sea Transform Fault borders the Arabian Plate to the west and has experienced approximately 107 km of left-lateral displacement since the mid-Miocene, equivalent to approximately 6-10 mm/yr of slip on the fault. Finally, the sheet is bounded in the east by the Owen fault zone.

In the Dead Sea fault system, an increase in relative motion from 5.6 to 7.5 mm per year can be seen from south to north. 

Relative motions at other plate boundaries (including the Anatolian and Aegean subplate) are consistent with displacements reported in focal mechanisms for severe earthquakes—a magnitude greater than 6. 

The data relating to the sliding speed of the plate boundary faults (East Anatolian Fault, Dead Sea Fault, Red Sea Rift) are available.