1991 Racha earthquake

Earthquake in Racha, Georgian SSR August 2022 1991 Racha earthquake 1991-04-29 09:12:48 usp0004qza 336954 29 April 1991 13:13 Georgia 7.0 w y 17 kmhttp://www.ngdc.noaa.gov/nndc/struts/results?eq_0=5286&t=101650&s=13&d=22,26,13,12&nd=display https://web.archive.org/web/20200831010644/https://www.ngdc.noaa.gov/nndc/struts/results?eq_0=5286&t=101650&s=13&d=22,26,13,12&nd=display dead 31 August 2020 Comments for the Significant Earthquake NGDC 10 August 2010 Georgia 1990 Blind thrust 42.453 43.673 inline,title IXSignificant Earthquake Database https://www.ngdc.noaa.gov/hazel/view/hazards/earthquake/event-data?minIntensity=9&minYear=1900&maxIntensity=12&minDeaths=0&minEqMagnitude=6&minDeathsTotal=0 National Geophysical Data Center / World Data Service (NGDC/WDS) National Geophysical Data Center, NOAA 10.7289/V5TD9V7K 1972 Data SetIX 270 dead The 1991 Racha earthquake occurred in the province of Racha, Georgia, at 9:12 UTC on 29 April. Centered on the districts of Oni and Ambrolauri on the southern foothills of the Greater Caucasus mountains, it killed 270, left approximately 100,000 homeless and caused severe damage, including to several medieval monuments. It had a magnitude of 7.0 and was the most powerful earthquake recorded in the Caucasus. Tectonic setting Georgia lies between the two mountain chains of the Greater Caucasus in the north and the Lesser Caucasus in the south. These two sets of mountains have both resulted from the continuing effects of the collision between the Arabian plate and the Eurasian plate. The Greater Caucasus consists of a southward-directed fold and thrust belt that has been active since the Oligocene. Racha lies close to the southern margin of this thrust belt and the earthquake is interpreted to be caused by rupture of the active thrust front. Damage thumb|250px|USGS shake map for the earthquake The earthquake affected 700 villages and settlements, destroying 46,000 houses and making 100,000 people homeless. The number of casualties was reduced because most of the inhabitants were working in the fields at the time of the earthquake, 13:13 local time. Many important historical monuments were badly damaged, particularly the Archangel Church near Zemo Krikhi and the Mravaldzali church, which were completely destroyed.http://www.opentext.ge/art/archit/medieval/racha.htm Earthquake in Racha and Middle Age Monuments Nikoleishvili I. 10 August 2010 dead https://web.archive.org/web/20110721025942/http://www.opentext.ge/art/archit/medieval/racha.htm 21 July 2011 Zaalishvili V. Sulberidze O. Chelidze T. Varazanashvili O. Javakhishvili Z. amp Balassanian S. Cisternas A. Melkumyan M. Earthquake hazard and seismic risk reduction https://books.google.com/books?id=MwUEbRU6oXAC&pg=PA127 Advances in natural and technological hazards research 12 2000 978-0-7923-6390-3 127–136 Seismicity and cultural monuments of Georgia Much of the damage associated with the earthquake was caused by landslides triggered by the shaking, rather than the shaking itself. The most common type were rock falls, followed by debris slides, slumps, earth slides, rock-block slides and rock avalanches. The most destructive was a large debris avalanche, which destroyed the village of Khokheti, killing 50 of the inhabitants. A large mass of Jurassic volcanic rock fell onto water-saturated alluvium, combining to form the debris avalanche. The debris avalanche, which had an estimated volume of over 3 million m3, swept down a valley through Khokheti, blocking the Gebura River, forming a 100-m-high dam, that breached soon afterwards, causing more destruction. Two of the earth slides showed a delayed movement, with most displacement occurring a few days after the main shock. The Chordi landslide was active before the earthquake and showed only minor movement at the time of the main shock. Two to three days later, the slide started to move at about 8 m per day, destroying the village of Chordi. On 18 May, the slide was still moving at 2 m per day. This slide moved on claystone of the Maikop Formation and had a total volume of about 20 million m3.Jibson R.W. Prentice C.S. Borissoff B.A. Rogozhin E.A. Langer C.J. amp 1994 Some Observations of Landslides Triggered by the 29 April 1991 Racha Earthquake, Republic of Georgia Bulletin of the Seismological Society of America 84 4 https://profile.usgs.gov/myscience/upload_folder/ci2009Apr221601094273745-Racha%20landslides,%20BSSA.pdf 10 August 2010 https://web.archive.org/web/20100531195424/http://profile.usgs.gov/myscience/upload_folder/ci2009Apr221601094273745-Racha%20landslides,%20BSSA.pdf 31 May 2010 dead The large aftershock on 15 June caused extensive damage in the Java to Tskhinvali area. At least 8 people were killed and 200 injured. However, due to a protest rally by the local people, dozens, but not hundreds, were killed. The village of Khakhet was destroyed.http://www.liveinternet.ru/users/2021656/post82149008 История конфликта в Южной Осетии. Обсуждение на LiveInternet – Российский Сервис Онлайн-Дневников Characteristics The earthquake had a magnitude of 7.0. A maximum intensity of IX on the MSK scale was observed. The calculated focal mechanism showed that the earthquake was a result of low-angle reverse faulting on a fault plane dipping at about 35° to the north-northeast. This was confirmed from the distribution of aftershocks, which defined a clear plane of this orientation. Analysis of the detailed velocity structure around the rupture zone suggested that it coincided with a marked change in seismic velocity, consistent with it representing the interface between Mesozoic sediments and the underlying crystalline basement.Arafiev S.S. Rogozhin E.A. Bykova V.V. Dorbath C. amp 2006 Deep Structure of the Racha Earthquake Source Zone from Seismic Tomography Data Izvestiya, Physics of the Solid Earth 42 1 27–40 http://horizon.documentation.ird.fr/exl-doc/AInv/2006_PSE_Racha.pdf 10.1134/s1069351306010034 2006IzPSE..42...27A 128784815 dead https://web.archive.org/web/20110807114528/http://horizon.documentation.ird.fr/exl-doc/AInv/2006_PSE_Racha.pdf 7 August 2011 The 1,500-m-high Racha Ridge is thought to have been uplifted by repeated earthquakes of this type.Triep E.G. Abers G.A. Lerner-Lahm A.L. Mishatkin V. Zakharchenko N. Starovoit O. amp 1995 Active thrust front of the Greater Caucasus: The April 29, 1991, Racha earthquake sequence and its tectonic implications Journal of Geophysical Research 100 B3 4011–4033 10.1029/94JB02597 http://people.bu.edu/abers/papers/Triep++94JB02597.pdf 10 August 2010 1995JGR...100.4011T dead https://web.archive.org/web/20110622025917/http://people.bu.edu/abers/papers/Triep%2B%2B94JB02597.pdf 22 June 2011 The mainshock was followed by a complex series of aftershocks extending over several months, which caused further damage and casualties The largest of the aftershocks, which consisted of two events about two seconds apart, had a magnitude of s y 6.5 and occurred on 15 June with an epicenter near Java.https://earthquake.usgs.gov/earthquakes/eqarchives/significant/sig_1991.php Significant Earthquakes of the World 1991 United States Geological Survey 5 January 2010 10 August 2010 dead https://web.archive.org/web/20090116165450/http://www.laprensagrafica.com/index.php/internacionales/mundo/11435.html 16 January 2009 On 23 October 1992, a magnitude 6.7 earthquake occurred about 100 km east of the aftershock zone. It was also due to reverse faulting on a north-northeast-dipping plane, although with a significant dextral (right lateral) strike-slip component. Aftermath The ongoing Georgian–Ossetian conflict complicated the rescue effort.http://seismos-u.ifz.ru/1991-1999.htm 1991–1999 20 September 2009 https://web.archive.org/web/20090521141603/http://seismos-u.ifz.ru/1991-1999.htm 21 May 2009 dead See also List of earthquakes in 1991 List of earthquakes in Georgia (country) References The Geology of Earthquakes R. S. Yeats K. E. Sieh Kerry Sieh C. R. Allen Clarence Allen (geologist) 1997 978-0-19-507827-5 Oxford University Press 363 External links 336954 Category:Buried rupture earthquakes Category:Earthquakes in Georgia (country) Racha earthquake Racha Category:1991 disasters in the Soviet Union Category:Earthquakes in the Soviet Union Category:Geology of Georgia (country) Category:Racha Category:April 1991 in Asia Category:1991 disasters in Georgia (country)