1978 Tabas earthquake: Difference between revisions
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The '''1978 Tabas earthquake''' was an earthquake measuring 7.8 on the [[Richter magnitude scale|Richter scale]] which struck on September 16, 1978 in central Iran. The death toll was approximately 15,000<ref name="USGS"/> and the worst damage was to the town [[Tabas]], which was at the epicentre of the quake and completely flattened. 40 villages within a {{convert|30|mi|km}} radius were damaged. <!-- Around 15,000 population were killed,<ref name="USGS"/> leaving only 4,000 living in the town. --> All the town's doctors were reported to have died, leaving civilians to treat others. All water and electricity was cut from Tabas, along with phone lines. The nearest accessible place to gain water was the town of [[Ferdows]], a three hour drive away. |
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The September 16, 1978 (Shahrivar 25, 1957 Iranian solar year) destructive earthquake of magnitude Mw 7.3 and intensity of IX+ at 19:36 Tehran local time (19:36 GMT) devastated the isolated and thinly populated town of Tabas-e-Golshan and the surrounding villages, west of the Shotori mountain, on the 38th anniversary day of Mohammad Reza Shah Pahlavi's reign during political turmoil period. It was one of the largest events of the instrumental era to occur in Iran [1]. |
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Despite (i) the pre-1978 long-term seismic precursors, (ii) shifting of seismic activity from the 1939.06.10 (mb 5.5, Io VII+) Baharestan earthquake in NW, to the 1974.06.17 (mb 4.8, Io VII+) and 1974.06.24 Posha, and the 1977.09.26 (Io VI) Tabas earthquakes, and (iii) the clear evidence of young faulting on aerial photographs and on the ground surface, the pre-1978 events were not known and the active fault was not mapped or recognized prior to the 1978 catastrophic earthquake of Tabas-e-Golshan [1]. |
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There were no foreshocks, but some unusual premonitory occurrences such as abnormal animal behavior and the appearance of a glow over the Shotori Mountain were reported. The main shock was preceded by a strong roaring noise which was reported by many survivors. The time lapse between the roaring noise and first arrival of the tremor is estimated to be about 4 to 4.5 seconds. As the warning given by this precursory signal was short, only few people reacted fast enough to save their lives by running outdoors. The only epicenter located in a radius of less than 100 km around the town of Tabas-e-Golshan in 1978 is the one of 1978.08.06. ISC epicenter (with 9 readings) is located about 90 km southwest of Tabas, which SNFU location (with 6 readings, Ml 4.0, rms 0.60s, q d) is located 60km SW of Tabas. No macroseismic data is available, but the newspapers should be checked [1, 2]. |
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The earthquake killed more than 20,000 people, destroyed or severely damaged about 90 villages, slightly damaged another fifty villages in the region, and completely demolished the ever-green oasis town of Tabas-e-Golshan, where 85% of the inhabitants were killed (11,000 out of 13,000). The earthquake, which was strongly felt over an area of 1,130,000 km2, destroyed over 15,000 housing units and over 30 qanats in the epicentral region. Had the earthquake happened in a populated area such as Tehran, or other large cities, the casualty figures and destructions would have been infinitely greater [1]. [Official death toll: 6,363; 3,662 in Tabas-e Golshan & 2,701 in the villages13]. |
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The earthquake was felt in the capital city of Tehran (610 km to the west of Tabas-e-Golshan), where window panes trembled and caused panic among people. The lunar eclipse two hours after the main shock, together with the breakdown of the Tabas Power Station during the earthquake, and the tense political situation at that time, made it impossible for survivors to start the immediate rescue operation of their families and neighbors, and caused serious rescue problems. The rescue operation started in the morning of the next day, roughly 12 hours after the disaster struck [1, 2]. |
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The settlements in the Tabas-e-Golshan region, like other parts of the country, conform to a uniform traditional building style with small variations. The style in the epicentral area, including Tabas-e-Golshan town, consists of sun-dried brick with wooden beams or domed heavy roofs, mud-wall constructions and masonry buildings with mud mortar. Only some schools and some governmental buildings in the town or large villages were brick masonry with steel-beam jack-arch roofs. Damage was less serious to the few well built dwellings, while elevated water tanks made of steel sustained little damage [1, 2]. |
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The intensity values assigned to the damage area ranged from VI to X (MMI). The highest intensity of IX-X (80-100% destruction with 50-85% casualty of the inhabitants) covered an area of about 800 km 2 and was experienced approximately for 80 km along the ground rupture and roughly about 3 km on either side of it. In this zone, heavy objects like the Tabas power generator (weighing more than 50 tons) and the diesel reservoir-tank of the Tabas Power Station (containing 50,000 liters of diesel fuel at the time of the earthquake) installed on the footwall block (west of the Tabas earthquake thrust) broke their bolts and were shifted for about 80 and 17 cm respectively towards east, although a lightweight generator failed to break its bolts and remained anchored to the ground. Traditional partly underground domed water reservoir in Tabas town is one of the few constructions which did not collapse during the earthquake [1, 2]. |
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The very damaging intensity of VIII (50-58% destruction with 10-30% casualty of the inhabitants) covered an area of 1000 km2 and was generated for 100 km along the earthquake fault and roughly 10 km from it. The damaging intensity of VII (20-50% destruction) covered 3600 km2 and extended for 110 km along and about 60 km across the fault. The approximate limit of the building destruction and severe damage stopped about 45 km away from the ground rupture. Damage to buildings was caused mostly by earthquake shaking and in a few cases by landslides triggered by the earthquake. The damage zone was more extensive in the alluvial plain (Tabas playa) than in the mountains to the east of Tabas, where the villages were built on bedrock [1, 2]. |
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There were few damaging aftershocks, the largest of them took place on 1978.12.06 (Ms 5.2), 1979.02.13 (Ms 5.5), and 1980.01.12 (Ms 6.0). A detailed aftershock study of the Tabas-e-Golshan earthquake recorded thousands of shocks using smoked drum recorders[4, 5]. Out of 1560 located events, 329 best-located aftershocks passed a strict quality criterion. Almost all best located aftershocks follow very closely the pattern of the Tabas earthquake thrust at the surface and lie predominantly on the ENE side of the surface breaks in the hanging-wall block of the active thrust. The complex distribution of the best located aftershocks occur in a volume rather than along a single plane and are interpreted as resulting from hanging wall deformation. The hypocenters occurred mainly at depth less than 23 km with a high concentration of seismic activity 8-14 km depth. Therefore, based on the aftershock distribution, faulting seems to have been concentrated above 20 km. The best-located aftershocks with their well-constrained focal mechanisms clearly demonstrate an active imbricate listric thrust system with fault planes flattening into a basement decollement zone, and the reactivation of different basement reverse faults in response to a considerable amount of shortening of the top sedimentary cover. The sense of motion was almost universally thrusting and the aftershocks shared the same tectonic causes as the main shock [4, 5]. |
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The earthquake lasted around three minutes<ref>http://www.globalquakemodel.org/system/files/doc/Meetings/WG_Meetings-London-FebMarch2011/GEM_TE-Tabas.pdf</ref>, compared to the normal earthquake duration of 10 – 20 seconds. It struck at 19:38 local time. In the aftermath of the quake, bodies were burned where found to prevent the spread of disease. |
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== Notes == |
== Notes == |
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==External links== |
==External links== |
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1. Berberian, M., 1979. Earthquake faulting and bedding thrust associated with the Tabas-e-Golshan (Iran) earthquake of September 16, 1978. Bull. Seism. Soc. Am., 69(6), 1861-1887. |
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2. Berberian, M., 1979- Tabas-e-Golshan (Iran) catastrophic earthquake of September 16, 1978; a preliminary field report. Disaster, 2(4), 207-219. |
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3. Markaz Amar Iran, Mehr 1357. Statistical Center of Iran, http://www.amar.org.ir. |
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4. Berberian, M., Asudeh, I., Bilham, R.G., Scholz, C.H., and Soufleris, C., 1979. Mechanism of the main shock and the aftershock study of the Tabas-e-Golshan (Iran) earthquake of September 16, 1978; a preliminary report. Bull. Seism. Soc. Am., 69(6), 1851-1859. |
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5. Berberian, M., 1982- Aftershock tectonics of the 1978 Tabas-e-Golshan (Iran) earthquake sequence: a documented active 'thin-and thick-skinned tectonic' case. Geophys. J.R. Astr. Soc. London, 68, 499-530. |
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* [http://libraryphoto.cr.usgs.gov/cgi-bin/show_picture.cgi?ID=ID.%20Earthquake%20Information%20Bulletin%20298 Photograph showing damage from Tabas quake] photo by N. Orsini |
* [http://libraryphoto.cr.usgs.gov/cgi-bin/show_picture.cgi?ID=ID.%20Earthquake%20Information%20Bulletin%20298 Photograph showing damage from Tabas quake] photo by N. Orsini |
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Revision as of 03:06, 3 November 2012
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| UTC time | ?? |
|---|---|
| Magnitude | 7.8 ML[1] |
| Epicenter | 33°12′N 57°24′E / 33.2°N 57.4°E |
| Areas affected |  Iran |
| Casualties | ~15,000 dead[1] |
The 1978 Tabas earthquake was an earthquake measuring 7.8 on the Richter scale which struck on September 16, 1978 in central Iran. The death toll was approximately 15,000[1] and the worst damage was to the town Tabas, which was at the epicentre of the quake and completely flattened. 40 villages within a 30 miles (48 km) radius were damaged. All the town's doctors were reported to have died, leaving civilians to treat others. All water and electricity was cut from Tabas, along with phone lines. The nearest accessible place to gain water was the town of Ferdows, a three hour drive away.
The earthquake lasted around three minutes[2], compared to the normal earthquake duration of 10 – 20 seconds. It struck at 19:38 local time. In the aftermath of the quake, bodies were burned where found to prevent the spread of disease.
Notes
External links
- Photograph showing damage from Tabas quake photo by N. Orsini
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