1957 Sangchal earthquake
   Tehran | |
| UTCtime | 1957-07-02 00:42:26 |
|---|---|
| ISCevent | 886779 |
| USGS-ANSS | ComCat |
| Local date | July 2, 1957 |
| Magnitude | 6.6–7.1Mw |
| Depth | 15 km (9 mi) |
| Epicenter | 36°16′37″N52°46′41″E/ 36.277°N 52.778°E[1] |
| Type | Strike-slip |
| Areas affected | Iran |
| Total damage | US$25 million |
| Max.intensity | MMI IX (Violent) |
| Casualties | 1,500 killed |
The1957 Sangchal earthquakestruck northern Iran'sMazandaran provinceon 2 July 1957. It had amoment magnitudeof 6.6 or 7.1 (Mw ), focal depth of 15 km (9.3 mi),[1]and maximumModified Mercalli intensityof IX (Violent).[2]It devastated many communities in theAlborz Mountainsand caused an estimated 1,500 fatalities. Damage was estimated at US$25 million.
Tectonic setting[edit]
TheIranian plateauis a region of highly deformed crust wedged between theArabian Plateto the southwest andEurasian Plateto the northeast.Crustal deformationis dictated by the 22 cm (8.7 in)/yr oblique-convergencebetween the two tectonic plates. Deformation is accommodated by reverse and strike-slip faulting. In northern and southern Iran, thrusting allows convergence throughcrustal thickeningto take place. Most of the convergence is accommodated alongfold and thrust beltsof theZagros,Alborz,Kopet Dagmountains, and in eastern Iran, where seismicity is high. Seismicity in the central plateau is low due to its geology consisting of rigid and aseismictectonic blocks.[3]
Earthquake[edit]
The earthquake was the result of shallowthrust faultingalong the Larzaneh Fault, a shallow south-dipping thrust fault in the Alborz Mountains. Themainshockrupturedacross a 50 km (31 mi) × 25 km (16 mi) area. It is the second largest instrumentally recorded earthquake in the mountains, behind the1990 Manjil–Rudbar earthquake.The earthquake beneath the mountains occurred in a region of northwest–southeast trending reverse faults; near the interconnection of two antithetic reverse faults where the western Larzaneh Fault terminates. The fault links to another thrust fault via a linkage fault dipping southwest and extending to the northwest.[3]
No coseismicsurface faultingwas associated with the earthquake and there were no anomalies infumarolic activityonMount Damavanddespite its epicenter within 100 km (62 mi) of the volcano.[4]However, some fault movement was observed along the Amir Fault Zone, a south-dipping reverse fault. Fresh cracks were reported along a road that crosses the fault after the earthquake. There were unconfirmed reports of large fissures measuring several kilometers long in the mountainous area, north of Sang Chal.Nicholas Ambraseysalso documented 3 km (1.9 mi) of surface faulting which were not coseismic. These cracks were explained as triggered landslides or other natural events other than faulting.[5]
Impact[edit]
Themeizoseismal areawas located between theHarazandTalarrivers; encompassing thedehestansof Band Pay, Beh, Dala Rustaq and Chalav. There, around 120 villages were levelled and 1,500 deaths were recorded. The villages ofSang Chal,Nandal,Chaliyasar, Nasal, Andavar and Pardimeh were the hardest-hit. In Burun, Varzaneh, Shanguldeh, Nal and Dinan, rockfalls and landslides caused further devastation. Rivers and streams were dammed by falling rocks and landslides; the Haraz River nearAliabadwas blocked by a 20 m (66 ft) high and 1 km (0.62 mi) long dam which formed a reservoir. There were few engineering infrastructures in the region; the only reported damage was along Haraz road, which was minimal. The abudments of an 80 m (260 ft) longmasonryarch bridgesunk, and its deck cracked. The lining of a tunnel linking Kuhrud andBayjanwas severely cracked and its haunch sheared. Minor damage was observed at a tunnel near Nur and on a wooden bridge in Aliabad.[4]
Damage beyond the meizoseismal area was less severe but widespread. The severity of damage decreased more dramatically with distance towards the northwest and southeast compared to the northeast and southwest. Damage was reported as far as Pul-i Safis, Shiragh and to theKaslian River.At Utu, near the Kaslian River, several homes collapsed. Caved roofs were reported inPolurandFashamwhile inTehran,some homes were damaged. Damage to buildings extended as far southeast as Firuzkuh. To the northwest, at Qaemshahr and Sari, some modern constructions were damaged. AnimamzadehatVānehand theEmamzadeh Hashem Shrinewere heavily damaged.[4]
See also[edit]
References[edit]
- ^abISC (27 June 2022),ISC-GEM Global Instrumental Earthquake Catalogue (1900–2009),Version 9.1,International Seismological Centre
- ^National Geophysical Data Center / World Data Service (NGDC/WDS) (1972),Significant Earthquake Database(Data Set),National Geophysical Data Center,NOAA,doi:10.7289/V5TD9V7K
- ^abAnsari 2021.
- ^abcAmbraseys & Melville 1982,p. 93–94.
- ^Tchalenko 1973,p. 310–320.
Sources
- Ambraseys, N. N.; Melville, C. P. (1982).A History of Persian Earthquakes.Cambridge University Press. pp. 93–94.doi:10.1016/B978-0-444-63292-0.00009-0.ISBN9780521021876.
- Tchalenko, J. (1973)."Recent destructive earthquakes in the CentraL Alborz (Iran)".Annals of Geophysics.26(2–3).doi:10.4401/ag-5015.
- Ansari, S. (2021). "Role of fault structural heterogeneity in nucleation location of the Mw ≥ 7 Earthquakes in Iran".Environmental Earth Sciences.80(730).Bibcode:2021EES....80..730A.doi:10.1007/s12665-021-10042-9.S2CID239771196.
External links[edit]
- TheInternational Seismological Centrehas abibliographyand/orauthoritative datafor this event.