The 1780 Tabriz earthquake occurred at 01:15 local time on 8 January. It had an estimated magnitude of 7.4 and a maximum felt intensity of IX 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 city of

Tabriz Tabriz ( fa, تبریز ; ) is a city in northwestern Iran, serving as the capital of East Azerbaijan Province. It is the List of largest cities of Iran, sixth-most-populous city in Iran. In the Quri Chay, Quru River valley in Iran's historic Aze ...

was almost completely destroyed. The number of reported casualties varies from 40,000 to as many as 200,000, with 50,000 being a more likely estimate.

Tectonic setting

lies within the complex zone of

collision In physics, a collision is any event in which two or more bodies exert forces on each other in a relatively short time. Although the most common use of the word ''collision'' refers to incidents in which two or more objects collide with great fo ...

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 ...

. The main structures accommodating this oblique collision are west-east trending

thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If ...

s and WNW-ESE trending dextral (right lateral)

strike-slip faults 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

North Tabriz Fault North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating direction or geography. Etymology The word ''north'' i ...

is an active 150 km long dextral strike-slip fault that passes close to the northern edge of Tabriz city. It has two main segments and an estimated overall slip rate of about 7 mm per year. The southeastern segment is interpreted to have ruptured in the 1721 Tabriz earthquake, while the northwestern segment ruptured during the 1780 earthquake. Both events produced associated

ground rupture In seismology, surface rupture (or ground rupture, or ground displacement) is the visible offset of the ground surface when an earthquake rupture along a fault affects the Earth's surface. Surface rupture is opposed by buried rupture, where the ...

, which is still observable. An average slip of about 4 m has been estimated for earthquakes along the northwestern segment. A recurrence interval of about 800 years has been estimated, suggesting that a major earthquake along this structure is unlikely in the next few centuries, although a recurrence interval of 250–300 years has also been proposed, indicating that there is potential for a major earthquake in the relatively near future.

Earthquake

The earthquake sequence started with a strong

foreshock A foreshock is an earthquake that occurs before a larger seismic event (the mainshock) and is related to it in both time and space. The designation of an earthquake as ''foreshock'', ''mainshock'' or aftershock is only possible after the full sequ ...

. The mainshock was felt over a large area, including at Divrigi over 700 km away. Aftershocks continued for several years, the most damaging being on 12 and 20 February. The observed surface fault break extended for 60 km. There is evidence of some vertical movement in addition to the horizontal displacement.

Damage

All buildings within the city of Tabriz were reported destroyed and similar levels of damage affected many villages in the neighbouring area. The degree of destruction may in part relate to the weakening effects of the 1721 earthquake, which also caused severe damage to the city.

References

{{Earthquakes in Iran Earthquakes in Iran History of Tabriz 1780s earthquakes 1780s in Iran