The 1949 Khait (Hoit) earthquake (russian: Хаитское землетрясение 1949 года; tg, Заминларзаи Ҳоит 1949) occurred at 09:45 local time (03:53 UTC) on 10 July in the

Gharm Oblast The Gharm Oblast (russian: Гармская область; tg, Вилояти Ғарм, translit=Viloyati Ğarm/Vilojati Ƣarm; fa, ولایت غرم, ''Velâyate Qarm'') was an oblast in the Tajik Soviet Socialist Republic in the Soviet Union f ...

region of the

Tajik SSR The Tajik Soviet Socialist Republic,, ''Çumhuriji Şūraviji Sotsialistiji Toçikiston''; russian: Таджикская Советская Социалистическая Республика, ''Tadzhikskaya Sovetskaya Sotsialisticheskaya Resp ...

of the

Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen national ...

(within the modern boundary of

Tajikistan Tajikistan (, ; tg, Тоҷикистон, Tojikiston; russian: Таджикистан, Tadzhikistan), officially the Republic of Tajikistan ( tg, Ҷумҳурии Тоҷикистон, Jumhurii Tojikiston), is a landlocked country in Centr ...

). It had a

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

of 7.5 and triggered a series of

landslide Landslides, also known as landslips, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, deep-seated grade (slope), slope failures, mudflows, and debris flows. Landslides occur in a variety of ...

s that together led to 7,200 deaths.

Tectonic setting

The

earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...

occurred in a tectonically complex region at the southern edge of the

Tien Shan The Tian Shan,, , otk, 𐰴𐰣 𐱅𐰭𐰼𐰃, , tr, Tanrı Dağı, mn, Тэнгэр уул, , ug, تەڭرىتاغ, , , kk, Тәңіртауы / Алатау, , , ky, Теңир-Тоо / Ала-Тоо, , , uz, Tyan-Shan / Tangritog‘ ...

. The southern margin of the Tien Shan is characterised by combination of dextral

strike-slip faulting In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

and southward

thrusting Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that sys ...

over the Tajik Basin to the south along the Gissar-Kokshaal fault zone. At the same time the Tajik Basin is being shortened in response to oblique collision with the

Pamirs The Pamir Mountains are a mountain range between Central Asia and Pakistan. It is located at a junction with other notable mountains, namely the Tian Shan, Karakoram, Kunlun, Hindu Kush and the Himalaya mountain ranges. They are among the world' ...

, forming a series of north-south to SW-NE trending thrust faults, the earthquake is thought to have been caused by movement on the Vakhsh thrust, one of these faults.

Damage

In the area of maximum felt intensity (>IX) most

kishlak Kishlak or qishlaq ( uz, qishloq, tk, gyşlag, tr, kışlak, az, qışlaq, fa, قشلاق), or qıştaq ( ky, кыштак) qıstaw ( kz, қыстау) is a rural settlement of semi-nomadic Turkic peoples of Central Asia and Azerbaijan. The ...

s were completely destroyed. Most of the fatalities were caused by numerous landslides triggered by the earthquake. The town of Khait (modern spelling ''Hoit'' ( tg, Ҳоит)) and the village of Khisorak were almost completely destroyed by the

Khait landslide The Khait or Hoit landslide occurred on July 10, 1949 in the Hoit district in the Gharm Oblast in the Tajik Soviet Socialist Republic, then part of the Soviet Union. 'Khait' is a transliteration from russian: Хаит; the local modern spelling is ...

. Numerous kishlaks in the Yasman River valley were overwhelmed by the

loess Loess (, ; from german: Löss ) is a clastic, predominantly silt-sized sediment that is formed by the accumulation of wind-blown dust. Ten percent of Earth's land area is covered by loess or similar deposits. Loess is a periglacial or aeolian ...

flowslide that swept down the whole length of the valley. Other kishlaks were destroyed by loess flowslides in the lower Obi-Kabud River valley and on the north side of the Surkhob River valley. Published estimates of the number of casualties range from 5,000 to 28,000. A more recent study, based on the size of affected settlements and the likely population density, gave an estimate of 7,200 of which about 800 were caused by the Khait landslide and 4,000 by the Yasman valley flowslide.

Characteristics

Earthquake

The main shock was preceded by two

foreshock A foreshock is an earthquake that occurs before a larger seismic event (the mainshock) and is related to it in both time and space. The designation of an earthquake as ''foreshock'', ''mainshock'' or aftershock is only possible after the full sequ ...

s (M5.1 and M5.6) on 8 July, just 12 minutes apart. The main shock had a magnitude of 7.4 calculated as the 'unified magnitude' using the 'Soviet Method'. The magnitude was recalculated as 7.5 on the

moment magnitude scale The moment magnitude scale (MMS; denoted explicitly with or Mw, and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. It was defined in a 1979 pape ...

in the ISC-GEM catalogue published in 2013.

Landslides

Most of the landslides triggered by the earthquake were loess flowslides, involving failure and flow of unconsolidated loess material. In the Yasman River valley, which lies almost entirely within the area of greatest felt intensity, a large number of such flowslides coalesced in tributary valleys before combining into one massive flowslide that travelled the length of the valley. The area covered by the Yasman valley slide is about 24.4 km², with a total estimated volume of 245 MCM (

million cubic metre The cubic metre (in Commonwealth English and international spelling as used by the International Bureau of Weights and Measures) or cubic meter (in American English) is the unit of volume in the International System of Units (SI). Its symbol is m ...

s). The

began as a rockslide but progressively entrained loess material. The rockslide was initiated by failure of part of the western flank of Chokrak Mountain. The landslide became more mobile once it began to entrain loess material and reached the Obi-Kabud River where it traversed the floodplain and surmounted a 25 m high

river terrace Fluvial terraces are elongated terraces that flank the sides of floodplains and fluvial valleys all over the world. They consist of a relatively level strip of land, called a "tread", separated from either an adjacent floodplain, other fluvial te ...

on the river's west bank. The estimated volume for this landslide is about 75 MCM. It travelled with an estimated velocity of about 40 m/s.

References

External links

* {{Earthquakes in 1949 Khait Khait earthquake Earthquakes in Tajikistan Earthquakes in the Soviet Union 20th century in Tajikistan Khait earthquake 1949 Khait earthquake 1949 Khait earthquake Khait earthquake 1949 disasters in the Soviet Union