1979 Ghaenat earthquakes

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1979 Ghaenat earthquakes
1979 Ghaenat earthquakes is located in Iran
Tehran
Tehran
1979 Ghaenat earthquakes
Strike-slip
Areas affectedIran
Max. intensityX (Extreme)
AftershocksMany. Largest is a Ms 6.0
Casualties297–440 dead, 279 injured

The 1979 Ghaenat earthquakes were a series of large earthquakes in

Modified Mercalli intensity of VIII (Severe) and X (Extreme),[3][4] respectively. The earthquakes caused extensive damage throughout northeastern Iran, killing an estimated 297 to 440 people and left at least 279 injured.[5]

Tectonic setting

Iran is situated within the

subducts beneath Iran along the Makran Trench. Shallow strike-slip and reverse faulting accommodate deformation in eastern Iran. Crustal shortening and thickening occur at fold and thrust belts along the Zagros, Alborz, and Kopet Dag ranges. Intraplate deformation 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.[3]

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 Mw 6.0 in 1976. Another large Ms 6.7 or Mw 6.5 shock on January 16, 1979, killing 200 people in the town of Bonzonabad.[4][7] The source fault of that event has not been identified yet although the Boznabad and Pavak faults were possible candidates.[8]

Korizan earthquake

The Ms 6.6 or Mw 6.8 earthquake of November 14 was the result of rupturing the Abiz Fault; a 20 km (12 mi) long,

strike-slip fault at a shallow depth of 9.2 km (5.7 mi).[10] A maximum horizontal slip of 1 km (0.62 mi) and some vertical displacements were recorded during field surveys after the earthquake.[11] The southern section of the earthquake surface rupture would move once again during the 1997 Qayen earthquake.[12] The Abiz Fault with an approximate length of 125 km (78 mi), is thought to have ruptured its entire length during large earthquakes in 1936 (Ms 6.0), 1997 (Mw 7.3), as well as the 1979 event. There were no prior rupture before the 20th century.[13][14]

A major aftershock of the November 14 earthquake registered Ms 6.0 or Mw 5.9 on December 7 was initially thought to have caused a 15 km (9.3 mi) long surface rupture to the north. The aftershock would have extended the rupture length of the Abiz Fault to a total of 35 km (22 mi), but additional research suggest the new ruptures formed during a subevent of the Mw 7.2 mainshock. It is unlikely that the 15 km (9.3 mi) of new surface ruptures were attributed to the Mw 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.[13]

Koli-Boniabad earthquake

The November 27 Ms 7.1 mainshock occurred as a result of strike-slip faulting for a length of 60 km (37 mi) along the left-lateral Dasht-e-Bayaz Fault. It had an estimated moment magnitude (Mw ) of 7.1–7.2.[6] This mainshock had a hypocenter depth of 7.9 km (4.9 mi).[1] The second rupture is nearly perpendicular to the prior rupture.[6] The same fault produced another deadly Ms 7.1 earthquake in 1968 to the west northwest. The 1968 earthquake ruptured the western section for the fault for about 80 km in length.[13] At least 10 km (6.2 mi) of the 1968 rupture was involved in the 1979 event.[13] The both earthquakes had similar focal mechanisms.

A maximum vertical surface displacement of 3.90 m (12.8 ft), and horizontal surface displacement of 2.55 m (8 ft 4 in) was measured, respectively. The

fault rupture propagated westward. The eastern end of the rupture was also the intersection point of the Abiz Fault's (which produced the November 14 event) northern termination.[3] During this mainshock, the northern termination of the November 14 event ruptured further northeast, joining the eastern section of the second rupture.[9]

Impact

The earthquake damaged or destroyed mainly

adobe-constructed buildings of the sun-dried clay type. Strong ground motion 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.[15]

Between 280 and 420 people died, with a further 279 injured in the November 14 earthquake.[16] 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. Most of the dead were reportedly young children left at home while their adult family members were working in the saffron fields.[15]

The second earthquake destroyed 10 villages.[4] Survivors of the earthquakes were relocated to other areas while some damaged villages were rebuilt by the government in the same place.[17] 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.[18]

See also

References

  1. ^ a b "International Seismological Centre Online Event Bibliography". ISC: On-Line Bulletin. International Seismological Centre. Retrieved 4 August 2021.
  2. ^ "M 7.1 - 56 km ENE of Q?'en, Iran". earthquake.usgs.gov. USGS. Retrieved 4 August 2021.
  3. ^
    S2CID 239771196
    .
  4. ^ . Retrieved 4 August 2021.
  5. ^ Carl W. Stover; Carl A. von Hake (1984). United States earthquakes, 1979, 1984, Open-File Report 84-979 (PDF). U.S. Geological Survey. pp. 138–140.
  6. ^ a b c Niazi, Mansour; Kanamori, Hiroo (1981). "Source parameters of 1978 Tabas and 1979 Qainat, Iran earthquakes from long-period surface waves" (PDF). Bulletin of the Seismological Society of America. 71 (4): 1201–1213.
  7. ^ "M 6.7 - 32 km NE of Q?'en, Iran". earthquake.usgs.gov. USGS. Retrieved 4 August 2021.
  8. S2CID 133502859
    .
  9. ^ .
  10. ^ "International Seismological Centre Online Event Bibliography". ISC: On-Line Bulletin. International Seismological Centre. Retrieved 4 August 2021.
  11. S2CID 128583149.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  12. .
  13. ^
    doi:10.1111/j.1365-246X.2011.05213.x.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  14. .
  15. ^ .
  16. ^ "Korizan-Khaf Earthquake of 14 November 1979, Ms6.6". Institute of Engineering Seismology and Earthquake Engineering. 14 November 2015. Retrieved 4 August 2021.
  17. ^ Reza Alaghebandian (1998). "Damage of Reinforced Concrete Frame Structures during the Iran-Qayen (Ardakul) Earthquake of May 10, 1997". Annual Papers on Concrete Engineering. Japan Concrete Engineering Association. 20 (3).
  18. ^ "زمین لرزه ۶ آذر ۱۳۵۸ (۲۷ نوامبر ۱۹۷۹) کولی-بنیاباد" (in Persian). Institute of Engineering Seismology and Earthquake Engineering. Retrieved 4 August 2021.