The 1977 Bob–Tangol earthquake (also known as the Gisk earthquake) struck Kerman province of

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 ...

on December 19 at 23:34 GMT. The earthquake destroyed homes and left thousands homeless. 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 VII (''Very strong'') was evaluated based on damage. Between 584 and 665 people perished while a further 500–1,000 were injured. Casualties from the earthquake was considered moderate due to the sparsely populated area it affected. 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 ...

measured 5.9 and struck at a depth of . It had a

strike-slip 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 ...

focal mechanism, which was unusual as the source structure was a thrust fault. It was part of a sequence of strong earthquakes along the Kuh Banan Fault. Preceded by foreshocks the month before, many residents became wary of a larger earthquake and took refuge outside their homes, contributing to the moderate death toll. However, there were none immediately before the mainshock so many were still in their homes when it struck. Aftershocks were felt for several months, some causing additional damage.

Tectonic setting

The

Iranian plateau The Iranian plateau or Persian plateau is a geological feature in Western Asia, Central Asia, and South Asia. It comprises part of the Eurasian Plate and is wedged between the Arabian Plate and the Indian Plate; situated between the Zagros ...

is a broad zone of deformed continental crust as it is wedged between 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 and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelago ...

plates. The Arabian Plate, located southeast of the plateau, undergoes oblique

convergence Convergence may refer to: Arts and media Literature *''Convergence'' (book series), edited by Ruth Nanda Anshen * "Convergence" (comics), two separate story lines published by DC Comics: **A four-part crossover storyline that united the four Wei ...

with the Eurasian Plate in the northeast at a rate of annually. Deformation of the crust is distributed non-uniformly by the

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 of 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 ...

; oceanic

lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust (geology), crust and the portion of the upper mantle (geology), mantle that behaves elastically on time sca ...

subduction Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

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 ...

; and strike-slip and reverse faulting within the plateau. The Iranian plateau itself is divided into rigid

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. These crustal blocks are aseismic, but at their boundaries, seismicity is high.

Earthquake

The northeastern boundary of the Zarand plain is well-expressed by a northwest–southeast range front. This also lies the Kuh Banan Fault (KBF), a steep, east-dipping

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 ...

measuring in length and

strikes Strike may refer to: People *Strike (surname) Physical confrontation or removal *Strike (attack), attack with an inanimate object or a part of the human body intended to cause harm *Airstrike, military strike by air forces on either a suspected ...

northwest–southeast. It caused the uplift of late

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...

and Lower

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

rocks over younger

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 ...

alluvium Alluvium (from Latin ''alluvius'', from ''alluere'' 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluv ...

. The fault showed active thrusting in the early

. The eastern side of the KBF is the mountainous range front which is likely the result of the uplift it caused. The KBF is part of a north–south to northwest–southeast striking system of right-lateral faults. These faults accommodate less than /yr of right-lateral

deformation Deformation can refer to: * Deformation (engineering), changes in an object's shape or form due to the application of a force or forces. ** Deformation (physics), such changes considered and analyzed as displacements of continuum bodies. * Defo ...

between central Iran and the

Lut desert The Lut Desert, widely referred to as Dasht-e Lut ( fa, دشت لوت, "Emptiness Plain"), is a large salt desert located in the provinces of Kerman Province, Kerman and Sistan and Baluchestan Province, Sistan and Baluchestan, Iran. It is the Li ...

. Seismic activity was first detected along the KBF on September 17 when a strong earthquake shook the region. Two shocks were felt on October 15 and November 7. The

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 ...

on November 9 damaged several villages. Two additional shocks occurred on November 10 and 13, respectively. No earthquakes were felt from November 13 to the day of the

mainshock In seismology, the mainshock is the largest earthquake in a sequence, sometimes preceded by one or more foreshocks, and almost always followed by many aftershocks. Foreshock A foreshock is an earthquake that occurs before a larger seismic eve ...

. Seismicity progressed southwards with the occurrence of the mainshock. The November 9 foreshock may have increased stress in the mainshock zone.

Aftershock In seismology, an aftershock is a smaller earthquake that follows a larger earthquake, in the same area of the main shock, caused as the displaced crust adjusts to the effects of the main shock. Large earthquakes can have hundreds to thousand ...

s were felt until April 2, 1978. The aftershocks which occurred within four months of the mainshock were restricted to the Bob–Tangol segment of the KBF. A strong aftershock on December 24 frightened residents and caused further damage. Seismicity on the KBF progressed northwest to

Behabad , native_name_lang = fa , settlement_type = City , image_skyline = , imagesize = , image_alt = , image_caption = , image_flag = , flag_alt = , im ...

, five months later, where a damaging earthquake struck on May 24, 1978. That earthquake also had a foreshock sequence which started two days before.

Mechanism

The mainshock was associated with dextral strike-slip faulting caused by rupturing the Bob–Tangol segment. A focal mechanism analysis displayed a minor thrust component, but was not observed during field research. There were no significant vertical ground displacements along the rupture zone. A

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 ...

and maximum slip of was measured. This strike-slip mechanism is unusual because it differs from the type of faulting associated with the fault that was responsible, indicating a evolvement in slip

vector Vector most often refers to: *Euclidean vector, a quantity with a magnitude and a direction *Vector (epidemiology), an agent that carries and transmits an infectious pathogen into another living organism Vector may also refer to: Mathematic ...

. Earlier surveys of the fault before the earthquake did not display any strike-slip movement.

Strong ground motion

The damaging effects of the earthquake were restricted to an area measuring by (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 ...

). Structures in the damage area were left in an extremely unsafe and dilapidated state. High-frequency and low amplitude shaking was inferred in the meizoseismal area. The shaking was insufficient in noticeably displacing objects on the ground. A

of VII (''Very strong'') was assessed at Dartangal, Gisk and Sarbagh, a zone along the rupture where damage was the greatest.

Adobe Adobe ( ; ) is a building material made from earth and organic materials. is Spanish for ''mudbrick''. In some English-speaking regions of Spanish heritage, such as the Southwestern United States, the term is used to refer to any kind of e ...

buildings on

bedrock In geology, bedrock is solid Rock (geology), rock that lies under loose material (regolith) within the crust (geology), crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface mater ...

near the rupture were damaged but not destroyed. It was evaluated that ground motion was extreme but of short duration—had it lasted longer, these weakened buildings would have been destroyed. Similarly-constructed homes located further southeast on the Zarand

plain In geography, a plain is a flat expanse of land that generally does not change much in elevation, and is primarily treeless. Plains occur as lowlands along valleys or at the base of mountains, as coastal plains, and as plateaus or uplands ...

were razed. This pattern of damage was likely due to the different types of ground or construction.

Impact

Between 584 and 665 people were killed, and up to 1,000 more were injured. The death toll was considered "moderate" as the mainshock only affected a sparsely populated area. In addition, the

on November 9 made residents take refuge in tents. The foreshock damaged and weakened homes in Dehzu village. There were no precursor seismic activity immediately before the mainshock, which would have alerted residents to flee their homes. Many residents were asleep in their stone or mud homes when the earthquake struck. The town of Zarand and four nearby settlements were heavily affected. Thousands were reported homeless. It was the third destructive earthquake to affect Iran that year—an earthquake in March caused 167 deaths and another in April killed 352 people. Many homes in the affected communities were double storey and had

vaulted In architecture, a vault (French ''voûte'', from Italian ''volta'') is a self-supporting arched form, usually of stone or brick, serving to cover a space with a ceiling or roof. As in building an arch, a temporary support is needed while ring ...

roofs. Very few intact homes could be repaired. The village of Gisk, home to 2,000 inhabitants, was levelled. The thick

masonry Masonry is the building of structures from individual units, which are often laid in and bound together by mortar; the term ''masonry'' can also refer to the units themselves. The common materials of masonry construction are bricks, building ...

walls of homes experienced lateral spreading, allowing roofs to collapse. At least 175 people died in Gisk. In Dartangal, a village of 400 families, many homes were razed and 382 people perished. At Sarbagh, 90 of its 200 residents were killed. Nearly every home in the village was flattened or sustained irrecoverable damage. Shaking was so strong that people were tossed to the ground. In Zarand, 16 people were killed or seriously hurt. About 250 homes were seriously damaged, and to another 900, damage was minor. Modern infrastructures were mostly unaffected. Damage to these structures, including a nearby

power station A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the generation of electric power. Power stations are generally connected to an electrical grid. Many p ...

, were non-structural and superficial. At Aqai, 12 homes were destroyed and two people died. Nearly all 45 homes in Dehzuiyeh were damaged and some roof collapses occurred—one fatality was reported.

Aftermath

A spokesman for the

Red Lion and Sun Society The Red Lion and Sun Society of Iran ( fa, انجمن شیر و خورشید سرخ ایران) was established in 1922 and admitted to the International Red Cross and Red Crescent Movement in 1923. However, some report the symbol was introduced ...

, a relief organization, said there were many casualties in the villages of Bab-Tanqal, Ghisak and Sarabagh, where the total population was 5,000. Many survivors lacked access to drinking water and were suffering from cold temperatures. Wet weather forecasted in the days after the disaster was anticipated to make rescue attempts challenging. Early reports of the death toll varied; the Red Lion and Sun Society said 80 bodies were recovered while government officials said that 343 were killed, citing rescuers. Rescuers said that the death toll could rise as they inspected levelled villages.

Armed forces A military, also known collectively as armed forces, is a heavily armed, highly organized force primarily intended for warfare. It is typically authorized and maintained by a sovereign state, with its members identifiable by their distinct ...

were instructed to assist in rescue operations. Soldiers and rescue workers used

kerosene lamp A kerosene lamp (also known as a paraffin lamp in some countries) is a type of lighting device that uses kerosene as a fuel. Kerosene lamps have a wick or mantle as light source, protected by a glass chimney or globe; lamps may be used on a t ...

s to assist in night time rescue efforts as they comb the debris. The homeless sought refuge at campsites. The

air force An air force – in the broadest sense – is the national military branch that primarily conducts aerial warfare. More specifically, it is the branch of a nation's armed services that is responsible for aerial warfare as distinct from an a ...

transported doctors, medical essentials, meals and tents. Several hundred helicopters were conveyed from a base in

Isfahan Isfahan ( fa, اصفهان, Esfahân ), from its Achaemenid empire, ancient designation ''Aspadana'' and, later, ''Spahan'' in Sassanian Empire, middle Persian, rendered in English as ''Ispahan'', is a major city in the Greater Isfahan Regio ...

. Injured survivors were taken onboard trains and helicopters to Kerman and Zarand for medical attention. When hospitals were overwhelmed, inhabitants of the cities invited survivors into their homes.

References

Sources * * * * * 1977 earthquakes Earthquakes in Iran 1977 in Iran December 1977 events in Asia History of Kerman Province Zarand County {{DEFAULTSORT:1977 Bob-Tangol earthquake