551 Beirut earthquake
Encyclopedia
The 551 Beirut earthquake occurred on 9 July of 551 AD. It had an estimated magnitude of about 7.6 on the moment magnitude scale
and a maximum felt intensity of X (Intense) on the Mercalli intensity scale
. It triggered a devastating tsunami which affected the coastal towns of Phoenicia
, causing great destruction and sinking many ships. Overall large numbers of people were reported killed, with one estimate of 30,000 by Antoninus of Piacenza
for Beirut
alone.
, which forms part of the boundary between the Arabian Plate
and the African Plate
. In Lebanon the fault zone forms a restraining bend associated with a right stepping offset of the fault trace. Transpression
al deformation associated with this bend has formed a number of thrust fault
s, such as the recently identified Mount Lebanon thrust, which underlies the city and is interpreted to crop out at the seabed offshore.
and other locations in the Jordan Valley associated with the 551 event have been re-analyzed, suggesting that a later earthquake was more likely to be responsible.
in the southwest to Antioch
in the north. The area of felt intensity of VIII or more extends from Tripoli
in the north to Tyre in the south. Estimates for the magnitude vary from 7.2 on the surface wave magnitude
scale to a possible 7.5 on the moment magnitude scale
. The rupture length is estimated to be greater than 100km and possibly as long as 150 km. The origin of the tsunami was thought to have been due to an underwater landslide triggered by an earthquake on the Dead Sea Transform itself. More recent analysis suggested that an offshore continuation of the Roum Fault mapped onshore was responsible. However, seabed surveys have discounted this possibility and the discovery of geologically recent fault scarps at seabed indicate that movement on the newly identified Mount Lebanon Thrust was the cause of the earthquake and the resulting tsunami. Quaternary
uplift recorded by a series of marine-cut terraces
between Tripoli and Beirut are consistent with continuing upward movement of the hanging wall of the proposed thrust. At a smaller scale, an uplifted vermetid
bench, which indicates vertical movement of about 80 cm, is dated to the sixth century A.D. Continued uplift above this thrust since the late Miocene
may explain the formation of the Mount Lebanon
range.
Moment magnitude scale
The moment magnitude scale is used by seismologists to measure the size of earthquakes in terms of the energy released. The magnitude is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of...
and a maximum felt intensity of X (Intense) on the Mercalli intensity scale
Mercalli intensity scale
The Mercalli intensity scale is a seismic scale used for measuring the intensity of an earthquake. It measures the effects of an earthquake, and is distinct from the moment magnitude M_w usually reported for an earthquake , which is a measure of the energy released...
. It triggered a devastating tsunami which affected the coastal towns of Phoenicia
Phoenicia
Phoenicia , was an ancient civilization in Canaan which covered most of the western, coastal part of the Fertile Crescent. Several major Phoenician cities were built on the coastline of the Mediterranean. It was an enterprising maritime trading culture that spread across the Mediterranean from 1550...
, causing great destruction and sinking many ships. Overall large numbers of people were reported killed, with one estimate of 30,000 by Antoninus of Piacenza
Antoninus of Piacenza
The sixth-century pilgrim Antoninus of Piacenza, or the Anonymous Pilgrim of Piacenza, who described the holy places of Jerusalem in the 570s is confused often with Saint Antoninus of Piacenza, who is venerated as a saint and martyr in the Roman Catholic Church, with a feast day of 13 November in...
for Beirut
Beirut
Beirut is the capital and largest city of Lebanon, with a population ranging from 1 million to more than 2 million . Located on a peninsula at the midpoint of Lebanon's Mediterranean coastline, it serves as the country's largest and main seaport, and also forms the Beirut Metropolitan...
alone.
Tectonic setting
Lebanon lies astride the Dead Sea TransformDead Sea Transform
The Dead Sea Transform fault system, also sometimes referred to as the Dead Sea Rift, is a geologic fault which runs from the Maras Triple Junction to the northern end of the Red Sea Rift...
, which forms part of the boundary between the Arabian Plate
Arabian Plate
The Arabian Plate is one of three tectonic plates which have been moving northward over millions of years and colliding with the Eurasian Plate...
and the African Plate
African Plate
The African Plate is a tectonic plate which includes the continent of Africa, as well as oceanic crust which lies between the continent and various surrounding ocean ridges.-Boundaries:...
. In Lebanon the fault zone forms a restraining bend associated with a right stepping offset of the fault trace. Transpression
Transpression
Transpression is a geological term used to describe a region of the Earth's crust that experiences strike-slip shear and a component of shortening, resulting in oblique shear. Transpression typically occurs at a regional scale, such as plate boundaries that have an oblique convergence. More...
al deformation associated with this bend has formed a number of thrust fault
Thrust fault
A thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger...
s, such as the recently identified Mount Lebanon thrust, which underlies the city and is interpreted to crop out at the seabed offshore.
Damage
There is little in the way of detailed descriptions of the damage caused by this earthquake in contemporary accounts. Sources refer to the coastal cities from Tyre to Tripoli being reduced to ruins with many thousands of casualties. Antoninus of Piacenza reported that 30,000 people died in Beirut alone. Reports of damage at PetraPetra
Petra is a historical and archaeological city in the Jordanian governorate of Ma'an that is famous for its rock cut architecture and water conduits system. Established sometime around the 6th century BC as the capital city of the Nabataeans, it is a symbol of Jordan as well as its most visited...
and other locations in the Jordan Valley associated with the 551 event have been re-analyzed, suggesting that a later earthquake was more likely to be responsible.
Earthquake
The earthquake was felt over a wide area from AlexandriaAlexandria
Alexandria is the second-largest city of Egypt, with a population of 4.1 million, extending about along the coast of the Mediterranean Sea in the north central part of the country; it is also the largest city lying directly on the Mediterranean coast. It is Egypt's largest seaport, serving...
in the southwest to Antioch
Antioch
Antioch on the Orontes was an ancient city on the eastern side of the Orontes River. It is near the modern city of Antakya, Turkey.Founded near the end of the 4th century BC by Seleucus I Nicator, one of Alexander the Great's generals, Antioch eventually rivaled Alexandria as the chief city of the...
in the north. The area of felt intensity of VIII or more extends from Tripoli
Tripoli, Lebanon
Tripoli is the largest city in northern Lebanon and the second-largest city in Lebanon. Situated 85 km north of the capital Beirut, Tripoli is the capital of the North Governorate and the Tripoli District. Geographically located on the east of the Mediterranean, the city's history dates back...
in the north to Tyre in the south. Estimates for the magnitude vary from 7.2 on the surface wave magnitude
Surface wave magnitude
The surface wave magnitude scale is one of the magnitude scales used in seismology to describe the size of an earthquake. It is based on measurements in Rayleigh surface waves that travel primarily along the uppermost layers of the earth...
scale to a possible 7.5 on the moment magnitude scale
Moment magnitude scale
The moment magnitude scale is used by seismologists to measure the size of earthquakes in terms of the energy released. The magnitude is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of...
. The rupture length is estimated to be greater than 100km and possibly as long as 150 km. The origin of the tsunami was thought to have been due to an underwater landslide triggered by an earthquake on the Dead Sea Transform itself. More recent analysis suggested that an offshore continuation of the Roum Fault mapped onshore was responsible. However, seabed surveys have discounted this possibility and the discovery of geologically recent fault scarps at seabed indicate that movement on the newly identified Mount Lebanon Thrust was the cause of the earthquake and the resulting tsunami. Quaternary
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...
uplift recorded by a series of marine-cut terraces
Wave-cut platform
A wave-cut platform, or shore platform is the narrow flat area often found at the base of a sea cliff or along the shoreline of a lake, bay, or sea that was created by the action of waves. Wave-cut platforms are often most obvious at low tide when they become visible as huge areas of flat rock...
between Tripoli and Beirut are consistent with continuing upward movement of the hanging wall of the proposed thrust. At a smaller scale, an uplifted vermetid
Vermetidae
Vermetidae, common name the worm snails or worm shells, is a taxonomic family of small to medium-sized sea snails, marine gastropod molluscs in the clade Littorinimorpha....
bench, which indicates vertical movement of about 80 cm, is dated to the sixth century A.D. Continued uplift above this thrust since the late Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
may explain the formation of the Mount Lebanon
Mount Lebanon
Mount Lebanon , as a geographic designation, is a Lebanese mountain range, averaging above 2,200 meters in height and receiving a substantial amount of precipitation, including snow, which averages around four meters deep. It extends across the whole country along about , parallel to the...
range.