1949 Khait earthquake
Encyclopedia
The 1949 Khait earthquake occurred at 09:45 local time (03:53 UTC
) on 10 July in the Gharm Oblast
region of Tajikistan
. It had a magnitude of 7.4 and triggered a series of landslide
s that together led to 7,200 deaths.
occurred in a tectonically complex region at the southern edge of the Tien Shan. The southern margin of the Tien Shan is characterised by combination of dextral strike-slip faulting and southward thrusting
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, 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.
s were completely destroyed. Most of the fatalities were caused by numerous landslides triggered by the earthquake. The town of Khait (modern spelling Hoit ) and the village of Khisorak were almost completely destroyed by the Khait landslide
. Numerous kishlaks in the Yasman River valley were overwhelmed by the loess
flowslide the 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.
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'.
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 on the river's west bank. The estimated volume for this landslide is about 75 Mm3. It travelled with an estimated velocity of about 40 m/s.
Coordinated Universal Time
Coordinated Universal Time is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose...
) on 10 July in the Gharm Oblast
Gharm Oblast
The Gharm Oblast was an oblast in the Tajik Soviet Socialist Republic in the Soviet Union from the 1920s to 1955. Its capital was Gharm. The population of Gharm were known as Gharmis, a term still used in Tajikistan today.-History:...
region of Tajikistan
Tajikistan
Tajikistan , officially the Republic of Tajikistan , is a mountainous landlocked country in Central Asia. Afghanistan borders it to the south, Uzbekistan to the west, Kyrgyzstan to the north, and China to the east....
. It had a magnitude of 7.4 and triggered a series of landslide
Landslide
A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...
s that together led to 7,200 deaths.
Tectonic setting
The earthquakeEarthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
occurred in a tectonically complex region at the southern edge of the Tien Shan. The southern margin of the Tien Shan is characterised by combination of dextral strike-slip faulting and southward thrusting
Thrust fault
A thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger...
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, 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 kishlakKishlak
Kishlak or qishlaq is a rural settlement of semi-nomadis Turkic peoples of Central Asia , in Afghanistan, and in other places...
s were completely destroyed. Most of the fatalities were caused by numerous landslides triggered by the earthquake. The town of Khait (modern spelling Hoit ) and the village of Khisorak were almost completely destroyed by the Khait landslide
Khait landslide
The Khait or Hoit landslide occurred on July 10, 1949 in the Hoit district in the Gharm Oblast in the Tajikistan, then part of the Soviet Union. The landslide was triggered by the 1949 Khait earthquake and buried 33 villages and has by some estimates killed 28,000 people...
. Numerous kishlaks in the Yasman River valley were overwhelmed by the loess
Loess
Loess is an aeolian sediment formed by the accumulation of wind-blown silt, typically in the 20–50 micrometre size range, twenty percent or less clay and the balance equal parts sand and silt that are loosely cemented by calcium carbonate...
flowslide the 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.
Earthquake
The main shock was preceded by two foreshockForeshock
A foreshock is an earthquake that occurs before a larger seismic event 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 event....
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'.
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 Mm3 (million cubic metres). The Khait landslideKhait landslide
The Khait or Hoit landslide occurred on July 10, 1949 in the Hoit district in the Gharm Oblast in the Tajikistan, then part of the Soviet Union. The landslide was triggered by the 1949 Khait earthquake and buried 33 villages and has by some estimates killed 28,000 people...
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 on the river's west bank. The estimated volume for this landslide is about 75 Mm3. It travelled with an estimated velocity of about 40 m/s.