The 856 Damghan earthquake or the 856 Qumis earthquake occurred on 22 December 856 (242 AH). The

earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...

had an estimated

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

of 7.9, and a maximum intensity of X (''Extreme'') on the

Mercalli intensity scale The Modified Mercalli intensity scale (MM, MMI, or MCS), developed from Giuseppe Mercalli's Mercalli intensity scale of 1902, is a seismic intensity scale used for measuring the intensity of shaking produced by an earthquake. It measures the eff ...

. The

meizoseismal area The meizoseismal area in an earthquake is the area of maximum damage. For example, in the Charleston, South Carolina, earthquake of 1886, the meizoseismal area was an area about twenty by thirty miles stretching northeast between Charleston and ...

(area of maximum damage) extended for about along the southern edge of the eastern

Alborz The Alborz ( fa, البرز) range, also spelled as Alburz, Elburz or Elborz, is a mountain range in northern Iran that stretches from the border of Azerbaijan along the western and entire southern coast of the Caspian Sea and finally runs nort ...

mountains of present-day

Iran Iran, officially the Islamic Republic of Iran, and also called Persia, is a country located in Western Asia. It is bordered by Iraq and Turkey to the west, by Azerbaijan and Armenia to the northwest, by the Caspian Sea and Turkmeni ...

including parts of

Tabaristan Tabaristan or Tabarestan ( fa, طبرستان, Ṭabarestān, or mzn, تبرستون, Tabarestun, ultimately from Middle Persian: , ''Tapur(i)stān''), was the name applied to a mountainous region located on the Caspian coast of northern Iran. ...

and

Gorgan Gorgan ( fa, گرگان ; also romanized as ''Gorgān'', ''Gurgān'', and ''Gurgan''), formerly Esterabad ( ; also romanized as ''Astarābād'', ''Asterabad'', and ''Esterābād''), is the capital city of Golestan Province, Iran. It lies appro ...

. The earthquake's

epicenter The epicenter, epicentre () or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates. Surface damage Before the instrumental pe ...

is estimated to be close to the city of

Damghan Damghan ( fa, دامغان, translit=Dāmghān) is the capital of Damghan County, Semnan Province, Iran. At the 2006 census, its population was 57,331, in 15,849 families. It is situated east of Tehran on the high-road to Mashad, at an elevatio ...

, which was then the capital of the Persian province of Qumis. It caused approximately 200,000 deaths and is listed by the

USGS The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, a ...

as the sixth deadliest earthquake in

recorded history Recorded history or written history describes the historical events that have been recorded in a written form or other documented communication which are subsequently evaluated by historians using the historical method. For broader world hist ...

. This death toll has been debated.

Tectonic setting

Iran lies within the complex zone of

continental collision In geology, continental collision is a phenomenon of plate tectonics that occurs at convergent boundaries. Continental collision is a variation on the fundamental process of subduction, whereby the subduction zone is destroyed, mountains prod ...

between the

Arabian Plate The Arabian Plate is a minor tectonic plate in the Northern and Eastern Hemispheres. It is one of the three continental plates (along with the African and the Indian Plates) that have been moving northward in geological history and collidin ...

and the

Eurasian Plate The Eurasian Plate is a tectonic plate that includes most of the continent of Eurasia (a landmass consisting of the traditional continents of Europe and Asia), with the notable exceptions of the Indian subcontinent, the Arabian subcontinent and ...

, which extends from the Bitlis- Zagros belt in the south to the

Greater Caucasus mountains The Greater Caucasus ( az, Böyük Qafqaz, Бөјүк Гафгаз, بيوک قافقاز; ka, დიდი კავკასიონი, ''Didi K’avk’asioni''; russian: Большой Кавказ, ''Bolshoy Kavkaz'', sometimes translat ...

, the Apsheron-Balkan Sill and the

Kopet Dag The Köpet Dag, Kopet Dagh, or Koppeh Dagh ( tk, Köpetdag; fa, کپه‌داغ), also known as the Turkmen-Khorasan Mountain Range, is a mountain range on the border between Turkmenistan and Iran that extends about along the border southeast o ...

mountains in the north. The epicentral area is located in the

mountain range, in which oblique north–south shortening is accommodated by a combination of

thrusting Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that sys ...

and sinistral (left-lateral)

strike-slip faulting In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

. The main active structure in the Qumis region is the Shahrud fault system, which extends for several hundred km. This zone of overall sinistral strike-slip consists of several fault strands, including the Damghan Fault, Northern Damghan Fault, and the Astaneh Fault System, all of which lie within the epicentral area and show evidence of displacement during the

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...

Earthquake characteristics

The earthquake occurred at night. The longest of the possible candidates for the source of the 856 earthquake is the 150 km long Astaneh Fault System. Trenching along one of the segments of the Astaneh Fault System has provided evidence of a significant earthquake along the fault that occurred well after 600 BC and before 1300 AD, consistent with the 856 event. Aftershocks affected the area for several years, probably including a damaging earthquake in western

Khurasan Greater Khorāsān,Dabeersiaghi, Commentary on Safarnâma-e Nâsir Khusraw, 6th Ed. Tehran, Zavvâr: 1375 (Solar Hijri Calendar) 235–236 or Khorāsān ( pal, Xwarāsān; fa, خراسان ), is a historical eastern region in the Iranian Plate ...

Damage

The area of significant damage extended along the Alborz for about , including the towns of Ahevanu, Astan, Tash,

Bastam Bastam ( fa, بسطام, also romanized as Basṭām; also known as Busṭām and Bisṭām) is a city in and capital of the Bastam District of Shahrud County, Semnan Province, Iran. At the 2006 census, its population was 7,382, in 1,997 families ...

and

Shahrud The Shahrud (Turkish ''Şehrud'' from Persian شاهرود, DMG ''šāh-i rūd'' or ''šāh-rūd'') was a short-necked lute, illustrated in the '' Surname-i Hümayun'', resembling an oud or barbat, but being much larger. The larger size gave t ...

, with almost all the villages in the area severely damaged.

Hecatompylos Qumis ( fa, قومس; Middle Persian ''𐭪𐭥𐭬𐭩𐭮 Kōmis''), also known as Hecatompylos ( grc, Ἑκατόμπυλος, in fa, صددروازه, ''Saddarvazeh'') was an ancient city which was the capital of the Arsacid dynasty by 200 ...

, now called Šahr-e Qumis, the former capital of the

Parthian Empire The Parthian Empire (), also known as the Arsacid Empire (), was a major Iranian political and cultural power in ancient Iran from 247 BC to 224 AD. Its latter name comes from its founder, Arsaces I, who led the Parni tribe in conque ...

, was destroyed. Half of Damghan and a third of the town of Bustam were also destroyed. The earthquake badly affected water supplies in the Qumis area, partly due to springs and

qanat A qanat or kārīz is a system for transporting water from an aquifer or water well to the surface, through an underground aqueduct; the system originated approximately 3,000 BC in what is now Iran. The function is essentially the same across ...

s drying up, but also because of landslides damming streams. The total death toll for the earthquake is reported as 200,000, with 45,096 casualties in the district of Damghan alone.

Aftermath

Šahr-e Qumis was so badly damaged that it appears to have been abandoned following the earthquake. The effects of the earthquake were still visible in the area between Bastam and Damghan 46 years later.

Future seismic hazard

From the results of trenching at a single site along the Astaneh Fault, a repeat period of about 3,700 years has been estimated and no large earthquakes have been recorded in the Damghan area since 856. However, further trenching studies are needed to establish whether the entire length of the fault is typically involved in a rupture event, or whether shorter segments may be responsible for smaller (although damaging) earthquakes with a shorter recurrence period.

References