The 1979 Ghaenat earthquakes were a series of large earthquakes in

Qaen County Qaen County ( fa, شهرستان قائن, also Romanized as Ghayen) is in South Khorasan province, Iran. The capital of the county is the city of Qaen. At the 2006 census, the county's population was 137,357 in 35,783 households. Retrieved 6 ...

, Khorasan Province, northeast

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 ...

, near the

Afghanistan Afghanistan, officially the Islamic Emirate of Afghanistan,; prs, امارت اسلامی افغانستان is a landlocked country located at the crossroads of Central Asia and South Asia. Referred to as the Heart of Asia, it is bordere ...

border. The first mainshock, known as the Korizan earthquake with a

surface wave magnitude The surface wave magnitude (M_s) scale is one of the magnitude scales used in seismology to describe the size of an earthquake. It is based on measurements of Rayleigh surface waves that travel along the uppermost layers of the Earth. This ma ...

() of 6.6 and

moment magnitude The moment magnitude scale (MMS; denoted explicitly with or Mw, and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. It was defined in a 1979 pape ...

() of 6.8, struck on November 14, while the 7.1 or 7.2 Koli-Boniabad earthquake struck on November 27. The two mainshocks were assigned a maximum

Modified Mercalli intensity 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 ...

of VIII (''Severe'') and X (''Extreme''), respectively. The earthquakes caused extensive damage throughout northeastern Iran, killing an estimated 297 to 440 people and left at least 279 injured.

Tectonic setting

Iran is situated within the

Alpide belt The Alpide belt or Alpine-Himalayan orogenic belt,K.M. Storetvedt, K. M., ''The Tethys Sea and the Alpine-Himalayan orogenic belt; mega-elements in a new global tectonic system,'' Physics of the Earth and Planetary Interiors, Volume 62, Issues 1 ...

, an active

orogenic belt An orogenic belt, or orogen, is a zone of Earth's crust affected by orogeny. An orogenic belt develops when a continental plate crumples and is uplifted to form one or more mountain ranges; this involves a series of geological processes collecti ...

that spans the entire country. This tectonic environment is influenced by the

oblique Oblique may refer to: * an alternative name for the character usually called a slash (punctuation) ( / ) * Oblique angle, in geometry *Oblique triangle, in geometry *Oblique lattice, in geometry * Oblique leaf base, a characteristic shape of the b ...

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 ...

of the

Arabian The Arabian Peninsula, (; ar, شِبْهُ الْجَزِيرَةِ الْعَرَبِيَّة, , "Arabian Peninsula" or , , "Island of the Arabs") or Arabia, is a peninsula of Western Asia, situated northeast of Africa on the Arabian Plate. ...

and

Eurasian Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern Hemisphere, Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Ja ...

Plates at an estimated rate of 22 mm/yr. Iran itself is situated on the Eurasian Plate, where it hosts complex zones of faults, forming

tectonic block A tectonic block is a part of the Earth's crust that can be treated as a solid rigid crustal block or lithospheric section. A tectonic block may be bounded by faults. It may move from one place to another because of a tectonic shift, and they ma ...

s within the country. In southeastern Iran, the Arabian Plate subducts beneath Iran along the

Makran Trench The Makran Trench is the physiographic expression of a subduction zone along the northeastern margin of the Gulf of Oman adjacent to the southwestern coast of Balochistan of Pakistan and the southeastern coast of Iran. In this region the oce ...

. Shallow strike-slip and reverse faulting accommodate deformation in eastern Iran. Crustal shortening and thickening occur at

fold and thrust belt A fold and thrust belt (FTB) is a series of mountainous foothills adjacent to an orogenic belt, which forms due to contractional tectonics. Fold and thrust belts commonly form in the forelands adjacent to major orogens as deformation propagates ou ...

s along the

Zagros The Zagros Mountains ( ar, جبال زاغروس, translit=Jibal Zaghrus; fa, کوه‌های زاگرس, Kuh hā-ye Zāgros; ku, چیاکانی زاگرۆس, translit=Çiyakani Zagros; Turkish: ''Zagros Dağları''; Luri: ''Kuh hā-ye Zāgro ...

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 ...

, and

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 ...

ranges.

Intraplate deformation Intraplate deformation is the folding, breaking, or flow of the Earth's crust within plates instead of at their margins. This process usually occurs in areas with especially weak crust and upper mantle, such as the Tibetan Plateau (Figure 1). Int ...

occur, mainly displaying reverse faulting at the southern and northern parts of Iran to accommodate the convergence via crustal uplift, and strike-slip faulting at the east and western ends, where the Arabian Plate slides past the adjacent crust. The tectonic setting contributes to shallow seismicity.

Earthquakes

The earthquake of November 27 was the strongest in the area since 1968. Between 1968 and 1979, the area was hit by strong earthquakes including a 6.0 in 1976. Another large 6.7 or 6.5 shock on January 16, 1979, killing 200 people in the town of Bonzonabad. The source fault of that event has not been identified yet although the Boznabad and Pavak faults were possible candidates.

Korizan earthquake

The 6.6 or 6.8 earthquake of November 14 was the result of rupturing the Abiz Fault, a north-south striking, right-lateral

strike-slip fault 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 ...

at a shallow depth of for a length of . A maximum horizontal slip of and some vertical displacements were recorded during field surveys after the earthquake. The southern section of the earthquake

surface 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 ...

would move once again during the

1997 Qayen earthquake The Qayen earthquake, also known as the Ardekul or Qaen earthquake, struck northern Iran's Khorasan Province in the vicinity of Qaen on May 10, 1997 at 07:57 UTC (12:57 local time). The largest in the area since 1990, the earthquake registered ...

. The -long Abiz Fault ruptured in its entirety during the 7.1 earthquake of 1997. There were no prior recorded rupture before the 20th century.

Koli-Boniabad earthquake

The November 27 7.1 mainshock occurred as a result of strike-slip faulting for a length of along the left-lateral Dasht-e-Bayaz Fault. It had an estimated moment magnitude () of 7.1–7.2. This mainshock had a hypocenter depth of . The second rupture is nearly perpendicular to the prior rupture. The same fault produced another deadly 7.1 earthquake in 1968 to the west northwest. The 1968 earthquake ruptured the western section for the fault for about in length. At least of the 1968 rupture was involved in the 1979 event. The both earthquakes displayed strike-slip

focal mechanism The focal mechanism of an earthquake describes the deformation in the source region that generates the seismic waves. In the case of a fault-related event it refers to the orientation of the fault plane that slipped and the slip vector and is ...

s. A maximum vertical surface displacement of , and horizontal surface displacement of was measured, respectively. The

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 ...

located at the eastern end of the surface rupture zone suggest the fault rupture propagated westward. The eastern end of the rupture was also the intersection point of the Abiz Fault's (source of the November 14 event) northern termination. During this mainshock, the northern termination of the November 14 event ruptured further northeast, joining the eastern section of the second rupture. The November 14 and December 7 earthquakes ruptured approximately of the Abiz Fault. It was involved in a 6.0 earthquake in 1936 which produced of surface rupture.

Kalat-e-Shur earthquake

Another earthquake measuring 6.0 or 6.1 on December 7 was initially thought to have caused a long surface rupture to the north. The aftershock would have extended the rupture length of the Abiz Fault to a total of , but these ruptures may have also formed during a subevent of the 7.2 shock. It is unlikely that the of new surface ruptures were attributed to the 5.9 mainshock, due to its moderate magnitude. The earthquake has been suggested to be on a separate north–south striking structure, away from the Abiz Fault.

Impact

The earthquake damaged or destroyed mainly adobe-constructed buildings of the sun-dried clay type.

Strong ground motion In seismology, strong ground motion is the strong earthquake shaking that occurs close to (less than about 50 km from) a causative fault. The strength of the shaking involved in strong ground motion usually overwhelms a seismometer, forci ...

mainly of horizontal fashion caused many walls of these structures to completely detach from its roof, resulting in a collapse. More recent construction of single-storey buildings suffered small damage and were mostly intact. In one village located along a hill, the most serious damage was observed at the summit, and appear to decrease in severity downhill, suggesting the seismic waves produced by the earthquake was amplified and reflected at higher elevations on the hill. This subjected structures at the top of the hill with more intense shaking than those on lower elevations. Between 280 and 420 people died, with a further 279 injured in the November 14 earthquake. Many villages were also badly damaged in the earthquake. The earthquake struck at 5:51 local time (IST) when many adult villagers were outside their homes harvesting

saffron Saffron () is a spice derived from the flower of ''Crocus sativus'', commonly known as the "saffron crocus". The vivid crimson stigma and styles, called threads, are collected and dried for use mainly as a seasoning and colouring agent i ...

. Most of the dead were reportedly young children left at home while their adult family members were working in the saffron fields. The second earthquake destroyed 10 villages. Survivors of the earthquakes were relocated to other areas while some damaged villages were rebuilt by the government in the same place. The second mainshock only resulted in 20 additional deaths and injured 24 people. The death toll from the second earthquake was smaller due to the low population density of the area when the quake struck.

References

{{Earthquakes in Iran Ghaenat earthquakes Ghaenat earthquakes Ghaenat, 1979 History of South Khorasan Province History of Khorasan History of Razavi Khorasan Province Earthquake clusters, swarms, and sequences Ghaenat earthquakes December 1979 events in Asia