By Mehdi Zare

The risk of a major earthquake in Lebanon

April 8, 2023 - 16:54

TEHRAN - After the earthquakes on 6 February 2023, Mw7.8 and Mw7.5 which caused extensive damages in Southern Turkey and northwest Syria, and more than 57000 victims, questions are raised on the possibility of similar events in Lebanon. 

This part of West Asia is located at the intersection of three main tectonic plates (i.e., African, Arabian, and Eurasian plates). The seismicity in the eastern Mediterranean region is mainly related to the northward movement of the Arabian plate. 

Total displacement since the Oligocene is estimated at about 107 km, with an annual rate of about 5 mm over the last 7-10 million years. Some of the most important earthquakes in West Asia have caused destruction in most of the countries in the region. The seismic zone and epicenters of the Gulf of Suez, the Gulf of Aqaba, Jordan, Syria, and Lebanon coincide with the Dead Sea fault zone.

Syria is located north of the Arabian Plate in the main tectonic zone: "Dead Sea fault system" is associated with the north-south strike-slip fault system, "Palmyrides tectonic shear zone" is associated with frequent folding, and the northeast-southwest strike fault system and finally the "tectonic zone of the Euphrates system" which is characterized by the northwest-southeast normal fault system. The most hazardous area in terms of seismicity is concentrated in the northwestern part of Syria (i.e., the cities of Iskenderun, Latakia, and Tartus). 

The western regions of Syria (Idlib, Aleppo, Iskenderun, Latakia, Tartus, Daraa, as well as a part of Hama regions) and the cities of Homs and Damascus, as well as some places in the center of Syria (Palmyra), are the main seismic areas in western Syria.

Jordan is separated from the African plate in the northwest of the Arabian plate along the Aqaba Dead Sea -Jordan Valley rift. This zone moves along the left-lateral slip along the Dead Sea transform fault. 

The Jordan Valley, a major part of the Dead Sea Transform Fault, is the most seismically active region in West Asia, with a four-thousand-year history of documented destructive earthquakes.

Lebanon is located along the Dead Sea fault system. The western part of Lebanon near the coastal area between Saida and Tripoli, where most of Lebanon's population and investments are concentrated, shows a "high seismic risk". 

The Dead Sea fault system consists of a series of 1000 km long strike-slip fault segments that form continental boundaries. This fault system between the Arabian and African plates has spread from the Gulf of Aqaba, at the northern end of the Red Sea, to the Arabian-Eurasian collision, in the southeast of Turkey. 

This fault system transfers a part of the divergence between the Arabian and African plates in the Red Sea, to a convergence movement between the Eurasians and Arabian plates.

The earthquake of October 11, 1138 - with an estimated magnitude of 7.1 - is listed as the third deadliest earthquake in history, as reports indicate that more than 200,000 people died in this earthquake. 

On August 13, 1822, another important historical earthquake destroyed Aleppo. Magnitude 7.0 was estimated for this earthquake, which was felt in a wide area including Rhodes, Cyprus, and Gaza. About 30,000 casualties have been reported for this incident.

From the devastating earthquakes of the second millennium BC to the 1927 Jericho earthquake, 21 have occurred over the past millennia, one event every 45 years. 

The most destructive of them are the earthquakes of 31 BC, 363, 749, and 1033 AD. The 1202 and 1759 Syrian earthquakes are probably the strongest historical earthquakes in the region. 
Some earthquakes were accompanied by tsunamis - notably in 92 BC, 115, 306, 502, 551, 881, and 1202 AD.

The earthquake of 846, an earthquake has severely damaged the Qubbat al-Sakhra (The Dome of the Rock), and Temple Mount in the Old City of Jerusalem. In the 1015 earthquake, the Dome of the Rock collapsed due to the earthquake. 

The 1033s series of earthquakes for 40 days, in the Jordan River Valley, destroyed Ramallah, Jericho, and Nablus and left 70,000 dead. In the earthquake of 1068, the earth ruptured in Wadi Araba.

A strong recent earthquake has occurred with a magnitude of 6.5 in 1989 in the Dead Sea fault zone.  A 90-kilometer section of the Jordan fault in the south of the Sea of Galilee may cause an earthquake with a magnitude of 7 to 7.4. 

The July 9, 551 earthquakes along the Lebanese coast near Beirut, with an estimated magnitude of 7.2, shocked a very large area in the eastern Mediterranean. 

This earthquake was accompanied by a tsunami along the coast of Lebanon, a landslide near the town of Al-Batron, and a large fire in Beirut. Heavy destruction with loss of life occurred in several Lebanese cities, especially Beirut, with a maximum intensity of 10, resulting in movement along the Roum fault as a left-lateral strike-slip in southern Lebanon.

In the Bitlis tectonic line and the Eastern Anatolian fault system, the Arabian plate collides with the Eurasian plate with a convergence speed of about 4-6 mm per year. 

The Dead Sea fault system extends from the Gulf of Aqaba to the border between Syria and Turkey near Antakya. In Lebanon, it includes two main Yammouneh faults in the northeast-southwest direction in the western Bekaa valley and the Roum fault in the south of Lebanon in the northwest-southeast direction, which extends to the city of Beirut. The northernmost part of the Yammouneh fault is the Al-Ghab fault and finally the Eastern Anatolian fault system in the north of Antakya.

The history of earthquakes in Lebanon clearly shows the earthquakes of 551 (coast of Beirut), 1202 (along Yammouneh fault), and 2 events in 1759 AD (along Rechaya fault and Serghaya fault). 

The magnitude of all three of these events was determined to be 7.0 or more and caused destruction in most of the coastal cities including Beirut, Tripoli, Jbeil, Saida, Tire, and also the ancient city of Baalbek. Lebanon's coast constitutes 225 km of the total 600 km of the eastern Mediterranean coastal area. 

Lebanon is located in the vicinity of the 1000 km fault of the fault system that extends from the bottom of the Red Sea to the Taurus Mountains in southern Turkey. 

This fault system, the Levantine or Dead Sea fault system, controls the major seismic activity in the eastern Mediterranean. The seismicity of Lebanon, Palestine, western Syria, and Jordan and the future of the seismicity of the mentioned areas, and the return of subsequent earthquakes should be measured and studied precisely according to this fault system.

Mehdi Zare is a professor at the International Institute of Earthquake Engineering and Seismology. 

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