{"id":17019,"date":"2016-08-11T06:37:08","date_gmt":"2016-08-11T06:37:08","guid":{"rendered":"http:\/\/www.iiees.ac.ir\/en\/?p=17019"},"modified":"2016-08-13T03:13:04","modified_gmt":"2016-08-13T03:13:04","slug":"ahar-varzeghan-twin-earthquakes-of-11-august-2012-mw-6-4-and-mw-6-3","status":"publish","type":"post","link":"http:\/\/old.iiees.ac.ir\/en\/ahar-varzeghan-twin-earthquakes-of-11-august-2012-mw-6-4-and-mw-6-3\/","title":{"rendered":"Ahar-Varzeghan Twin Earthquakes of 11 August 2012, Mw.6.4 and Mw.6.3"},"content":{"rendered":"

Ahar-Varzeghan Twin Earthquakes of 11 August 2012, Mw<\/sub>.6.4 and Mw<\/sub>.6.3<\/strong><\/p>\n

Two \u2029earthquakes \u2029occurred\u2029 in \u202911 \u2029August \u20292012\u2029 NW\u2029 Iran, \u2029Ahar \u2029region \u2029(60 km\u2029 NE \u2029Tabriz), \u2029first \u2029one \u2029in \u202916:53 \u2029local \u2029time \u2029(Mw 6.4; \u202923 km \u2029west \u2029of \u2029Ahar) \u2029and \u2029the \u2029second\u2029 one \u2029in \u202917:04 \u2029local \u2029time \u2029(Mw 6.3;\u2029 30 km \u2029west \u2029of \u2029Ahar)\u2029 [Iran \u2029local \u2029time; \u2029GMT +4:30; \u2029which \u2029is \u2029GMT+3:30,\u2029 and\u2029 there \u2029is \u2029+1:00 \u2029for\u2029 summer\u2029 time]. \u2029These \u2029earthquakes \u2029caused \u2029306 \u2029killed, \u20293037 \u2029injured\u2029 and \u202930000 \u2029homeless \u2029people\u2029 (based\u2029 on \u2029the \u2029declaration\u2029 of \u2029the \u2029Iranian \u2029health \u2029minister, \u202913 \u2029August \u20292012). \u2029These \u2029events \u2029caused\u2029 panic\u2029 in \u2029the \u2029cities \u2029of \u2029the \u2029epicentral \u2029region \u2029(specially \u2029in \u2029the \u2029cities \u2029of \u2029Ahar, \u2029Varzaghan,\u2029 Kalibar,\u2029 Haris,\u2029 and\u2029 in\u2029 Tabriz \u2029the \u2029greatest \u2029city\u2029 in\u2029 NW\u2029 Iran, \u2029having \u2029a \u2029population \u2029of \u2029about\u2029 1,5 \u2029million).\u2029 After\u2029 the \u2029mainshocks \u2029the \u2029people \u2029settled\u2029 in\u2029 outside \u2029of \u2029the \u2029buildings \u2029and \u2029slept \u2029in\u2029 the \u20292 \u2029nights\u2029 after \u2029the \u2029events.\u2029 Most\u2029 of\u2029 the \u2029damages \u2029are \u2029reported \u2029from\u2029 the\u2029 villages \u2029of \u2029Gourdeh,\u2029 and\u2029 Dino \u2029(of\u2029 Ahar\u2029city).\u2029This \u2029earthquake \u2029felt \u2029in \u2029the \u2029cities \u2029of \u2029Tabriz,\u2029 Marand, \u2029Shabastar,\u2029 Mamaghan\u2029and\u2029 Bostanabad \u2029in \u2029East \u2029Azarbayjan \u2029Province, \u2029Ardabil \u2029and \u2029Meshkin shahr \u2029in \u2029Ardebil \u2029Province,\u2029 Urumieh, \u2029Khoy \u2029and \u2029Salmas \u2029in\u2029 West \u2029Azarbayjan\u2029 Province, \u2029and\u2029 Astara, \u2029Rasht \u2029and \u2029Somehsara \u2029in\u2029 Gilan \u2029Province. \u2029There \u2029are \u2029110 \u2029aftershock\u2029s with\u2029a \u2029M>3.0 \u2029recorded\u2029 in \u2029IIEES\u2029 broadband\u2029 seismic\u2029 network\u2029 in \u2029the \u20291st<\/sup>\u2029 40 \u2029hours \u2029after\u2029 the \u2029twin \u2029events. In general, based on the aftershocks, the fault that caused this earthquake is a strike-slip with left-lateral motion in the Northeastern-Southwestern direction, with about 20 kilometers length, that is situated 15 kilometers west of Ahar. Considering the two big earthquakes, with many aftershocks, there is a low probability of a bigger earthquake from this fault. Based on the information from the national seismology center, there has been no sign of increased seismicity in Tabriz fault; therefore, this earthquake has not triggered the tension on the Tabriz fault. The city of Varzaghan is located on mild slope bedrock. Fine sediments could be seen near the river, and the ground water level is near the ground surface in these parts. Based on the structural damages seen in this city, damages decrease as one walks away from the riverside. However, structures constructed on the thick layers of saturated alluvium have been damaged more (surprisingly, with more damages on the lower stories). There was no sign of liquefaction. Also in villages with partial destruction, damages were focused on the steep lands, which could be related to topography effects. Due to lithology and morphology characteristics of Pliocene sediments (loose and discontinuous Conglomerates and layers of silt – clay) and their disperse distribution, there has been some great landslides during the past years in this area. By considering this fact, and the high probability of another landslide in the area, the survey group of IIEES focused on identifying this hazard. Beside some old landslides, the survey group found some new landslides caused by the recent earthquake. Most of these cases were seen in the slopes of Ahar-Khaje road (10 to 20 kilometers from Ahar, between Zanjirblagh and Yangje villages) and Varzaghan-Khaje (between Zaghanabad and Sarad villages), caused by the high loose embankments on the side road gables, and were not a big threat. However, in some cases, signs of big landslides in the mentioned areas could be seen, which threatens the main roads. One of these cases could be seen in the picture below on the eastern hillside of Khaje-Varzaghan road (after Chaykandi village). Two big landslides in the southern and northern slopes of the mountain have been activated. Also signs of the old and newly activated landslides could be easily seen in the eastern side of the river. There were many signs of small and big rock falls; however, they were more focused on the asphalted roads of Ahar-Kahje (10 to 20 kilometers from Ahar) and Varzaghan-Kahje (in Sarant to Zaghanabad villages). Most of the residential buildings in the mentioned villages were adobe, mud or un-reinforced masonry without any technical or engineering provisions. Lack of construction regulations and heavy materials has caused the destruction of more than 200 villages among the total 500 villages in this area (claimed by the local authorities). Inefficient connection of non-structural elements to the structure or huge structural deformations has caused big damages to the buildings expected to be constructed based on the codes and regulations, which has made the residents to leave the building and stay on tents beside their house. Based on the received information, there are hospitals in two of the three Cities of Ahar, Vazaghan and Haris. Haris Hospital was highly damaged and out of service. The Bagher\u2019ol-oloum Hospital in Ahar is a two-storey concrete building, which has received high damages in the non-structural parts and the facilities. Separation of dividing walls, big diagonal cracks in the walls, damaged ceilings, displacement of facilities like the fallen oxygen capsules and damages in the extension joints, were some of the defects seen by the group. Damages were more extensive in the second floor compared to the first floor. There was no structural damage in the Hospital\u2019s structure. However, the extent of non-structural damages has lowered the performance of the hospital, which is crucial after each disaster.<\/p>\n<\/div><\/section>\n

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