Sunday, 24 July 2011

Earthquake on the Kyrgyzstan/Uzbekistan Border, 20 July 2011; at least 14 people dead.

Slightly after 1.30 am local time on the 20th July 2011 (or slightly after 7.30 pm on the 19th July GMT) an earthquake stuck in the Fergana Valley on the Kyrgyzstan/Uzbekistan border. It had a magnitude of 6.1 on the Richter Scale, and was at a depth of 16 km; shallow enough to have a considerable effect at the surface. Although the epicenter was on the Kyrgyrzstan side of the border, the majority of the damage seems to have occurred on the more densely populated Uzbek side of the border.
The geology of the area is complex; the Pamir Mountains to the southeast are being forced north into the Kazakh Shield to the northeast by the northward movement of India, far to the south. This causes shear in the Fergana Basin, as the rocks are twisted anti-clockwise, leading to thrust and strike-slip faulting. A thrust fault occurs where rocks are forced up and over one another; in this instance the faulting would be a blind-thrust; a thrust that happens beneath the surface, causing notable effects (e.g. earthquakes) but not visible faulting at the surface. A strike-slip fault occurs where two sections of rock slide past one-another. The earthquake in the Fergana Valley is likely to have been a combination of the two.
No fatalities were reported in Kyrgyrzstan, though 15 people were injured. Between 200 and 600 houses were damaged or destroyed in Batken Province (where the earthquake occurred) and (neighboring) Osh Province.

A single fatality was reported in Tajikstan, though this was caused by somebody jumping out of a window in panic, rather than directly by the earthquake. There are also reports of fractures to a dam under construction, delaying work while engineers investigate the situation.

Across the border in Uzbekistan the situation it much more serious (and confused). The city of Fergana (sometimes Ferghana or Farghona), capital of Fergana Province, with a population of 214 000, lies just 42 km from the epicenter of the quake (the point at ground level directly above the centre of the quake). For several hours the Uzbek authorities denied that anything had happened at all. It now appears that at least 13 people have been killed, and 86 injured, 35 requiring hospital treatment. At least 800 buildings have been destroyed, including several deemed to be of historic significance. It is likely that there will be further reports of injuries and possibly deaths as much of the population lives in remote villages in the mountainous region, and few buildings are earthquake proofed in any way.

There have been three other major earthquakes in the vicinity within the last 40 years, though none of these have caused any reported fatalities, though the wider region has suffered a number of significant quakes.

A series of earthquakes in 2006/2007/2008 destroyed a large number of buildings in Osh Province, displaced several thousand people and caused many fatalities. The worst of these, in October 2008, caused 15 fatalities (including 41 children), and destroyed the towns of Nura and Kura. This earthquake also caused damage in the Xingjiang Uyghur Autonomous Region of China.

In July 2006 a pair of magnitude 4.5 earthquakes in the Khatlon region of Tajikistan killed three people and injured 19 more. It also destroyed several thousand (non-earthquake-proofed) houses and caused a collapse in infrastructure that lead to a malaria epidemic, amongst other problems.

In 1985 a magnitude 7.4 earthquake in Wuquia County, Xingjiang, China, that was felt across the Fergana Basin and as far away as Pakistan. 65 deaths were reported.

In April 1966 a 7.5 magnitude earthquake destroyed Tashkent, the capital of Uzbekistan, making about 300 000 people homeless (figures on fatalities are not available; the Soviet Union was not keen on admitting to catastrophes at the time.

The aftermath of the 1966 Tashkent Earthquake.

In July 1949 a magnitude 7.4 earthquake in the Gharm Oblast region of Tajikistan (then the Tajik Soviet Socialist Republic), causing a series of landslides and killing over 7000 people (some estimates are as high as 28 000 fatalities).

In 1931 a magnitude in Fuyun County, Xingjiang caused a surface rupture 171 km long, with a maximum horizontal displacement of 14 m. This is now preserved as part of the Koktokay National Geopark. This quake caused about 10 000 fatalities.

In 1907 a 7.4 magnitude earthquake near Qaratog (sometimes Karatog) on the Tajikistan/Uzbekistan border caused between 12 000 and 15 000 fatalities.

See also The End of the Cretaceous and Earthquakes on Sciency Thoughts YouTube.

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