The 1950 Assam–Tibet earthquake, also known as the Assam earthquake, occurred on 15 August and had a moment magnitude of 8.7. The epicentre was located in the Mishmi Hills. It is one of the strongest earthquakes ever recorded on land. Occurring on a Tuesday evening at 7:39 PM

Indian Standard Time Indian Standard Time (IST), sometimes also called India Standard Time, is the time zone observed throughout the Republic of India, with a time offset of UTC+05:30. India does not observe daylight saving time or other seasonal adjustments. I ...

, the

earthquake An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...

was destructive in both

Assam Assam (, , ) is a state in Northeast India, northeastern India, south of the eastern Himalayas along the Brahmaputra Valley, Brahmaputra and Barak River valleys. Assam covers an area of . It is the second largest state in Northeast India, nor ...

(India) and

Tibet Tibet (; ''Böd''; ), or Greater Tibet, is a region in the western part of East Asia, covering much of the Tibetan Plateau and spanning about . It is the homeland of the Tibetan people. Also resident on the plateau are other ethnic groups s ...

(China), and approximately 4,800 people were killed. The earthquake is notable as being the largest recorded quake caused by

continental collision In geology, continental collision is a phenomenon of plate tectonics that occurs at Convergent boundary, convergent boundaries. Continental collision is a variation on the fundamental process of subduction, whereby the subduction zone is destroy ...

rather than

subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...

, and is also notable for the loud noises produced by the quake and reported throughout the region.

Tectonic setting

Northeastern India and southern Tibet lie in the frontal part of the zone of

collision In physics, a collision is any event in which two or more bodies exert forces on each other in a relatively short time. Although the most common use of the word ''collision'' refers to incidents in which two or more objects collide with great for ...

between the northward moving

Indian plate The Indian plate (or India plate) is or was a minor tectonic plate straddling the equator in the Eastern Hemisphere. Originally a part of the ancient continent of Gondwana, the Indian plate broke away from the other fragments of Gondwana an ...

and

Eurasia Eurasia ( , ) is a continental area on Earth, comprising all of Europe and Asia. According to some geographers, Physical geography, physiographically, Eurasia is a single supercontinent. The concept of Europe and Asia as distinct continents d ...

. The thrust belt that marks this plate boundary zone is formed of a series of sub-parallel thrust faults. The thrust faults in this part of the Himalayas show a rapid lateral change in orientation from SW-NE trending to NW-SE trending in the area of the Namche–Barwa syntaxis. To the west the main active part of the thrust belt is the Himalayan (or Main) Frontal Thrust, which joins the

Main Himalayan Thrust The Main Himalayan Thrust (MHT) is a décollement under the Himalaya Range. This thrust fault follows a northwest-southeast strike, reminiscent of an arc, and gently dips about 10 degrees towards the north, beneath the region. It is the large ...

at depth. To the east the active frontal structure is the Mishmi Thrust, which connects to the south with the Naga Thrust and the left-lateral

strike-slip 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 ...

Sagaing Fault The Sagaing Fault is a major fault in Myanmar, a mainly continental right-lateral transform fault between the Indian plate and Sunda plate. It links the divergent boundary in the Andaman Sea with the zone of active continental collision along t ...

that together bound the Burma Microplate.

Past seismicity

In an attempt to further uncover the seismic history of

Northeast India Northeast India, officially the North Eastern Region (NER), is the easternmost region of India representing both a geographic and political Administrative divisions of India, administrative division of the country. It comprises eight States and ...

, field studies were conducted by scientists with the National Geophysical Research Institute and Institute of Physics, Bhubaneswar. The study discovered signs of

soil liquefaction Soil liquefaction occurs when a cohesionless saturated or partially saturated soil substantially loses Shear strength (soil), strength and stiffness in response to an applied Shear stress, stress such as shaking during an earthquake or other s ...

including sills and

sand volcano Sand boils, sand volcanoes, or sand blows occur when water under pressure wells up through a bed of sand. The water looks like it is boiling up from the bed of sand, hence the name. Sand volcano A sand volcano or sand blow is a cone of sand ...

es inside at least twelve

trench A trench is a type of digging, excavation or depression in the ground that is generally deeper than it is wide (as opposed to a swale (landform), swale or a bar ditch), and narrow compared with its length (as opposed to a simple hole or trapping ...

es in

alluvial fan An alluvial fan is an accumulation of sediments that fans outwards from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment. They are characteristic of mountainous terrain in arid to Semi-arid climate, semiar ...

s and on the Burhi Dihing River Valley that were formed by past

seismic activity An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...

Radiocarbon dating Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for Chronological dating, determining the age of an object containing organic material by using the properties of carbon-14, radiocarbon, a radioactive Isotop ...

identified the deposits at roughly 500 years old, which would correspond with a recorded earthquake in 1548.

Earthquake

The earthquake had an epicenter in the Mishmi Hills to the northeast of the surface trace of the Mishmi Thrust Fault. Magnitudes calculated for the earthquake range from 8.6–8.8, making it the largest onshore earthquake ever recorded and the largest not associated with

. It was the sixth largest earthquake of the 20th century.

Aftershock In seismology, an aftershock is a smaller earthquake that follows a larger earthquake, in Epicenter, the same area of the Mainshock, main shock, caused as the displaced Crust (geology), crust adjusts to the effects of the main shock. Large earthq ...

s were numerous; many of them were of magnitude 6 and over and well enough recorded at distant stations for reasonably good

epicentre The epicenter (), epicentre, or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates. Determination The primary purpose of a s ...

location. The aftershock epicenters covered a very large area over the Abor and Mishmi Hills of about 30,000 km², which matches well with the area of maximum shaking as determined from the location of landslides from satellite imagery. This is interpreted to define the rupture area. Evidence for

surface rupture In seismology, surface rupture (or ground rupture, or ground displacement) is the visible offset of the ground surface when an earthquake rupture along a Fault (geology), fault affects the Earth's surface. Surface rupture is opposed by buried rup ...

was discovered at multiple locations along the trace of the Abor Hills section of the Main Frontal Thrust (MFT) and along the Mishmi Thrust (MT). The total observed surface rupture length along both faults is ≥ 200 km. Published

focal mechanism The focal mechanism of an earthquake describes the Fault (geology)#Slip.2C heave.2C throw, deformation in the Hypocenter, source region that generates the seismic waves. In the case of a Fault (geology), fault-related event, it refers to the ori ...

s for this earthquake are contradictory with both thrust and strike-slip mechanisms supported. It has been proposed that the earthquake ruptured both the northwest- dipping MFT and the northeast-dipping MT. This combined source, being oblique thrust in nature, provides a good fit with observations of seismic arrivals. The average slip values on MT and MFT are 17 ± 1 m and 11 ± 1 m respectively, with an amount as high as 34 ± 2.5 m implied to have happened underneath Wakro in the former fault. Together with the calculated rupture area of 330 × 90 km and a reasonable estimate for the crustal rigidity, this gives a moment magnitude of 8.7.

Impact

The 1950 Assam–Tibet earthquake had devastating effects on both Assam and Tibet. In Assam, 1,526 fatalities were recorded and another 3,300 were reported in Tibet for a total of approximately 4,800 deaths. Alterations of relief were brought about by many rock falls in the Mishmi Hills and surrounding forested regions. In the Abor Hills, 70 villages were destroyed with 156 casualties due to landslides. Landslides blocked the tributaries of the

Brahmaputra The Brahmaputra is a trans-boundary river which flows through Southwestern China, Northeastern India, and Bangladesh. It is known as Brahmaputra or Luit in Assamese, Yarlung Tsangpo in Tibetan, the Siang/Dihang River in Arunachali, and ...

. In the Dibang Valley, a landslide lake burst without causing damage, but another at

Subansiri River The Subansiri (Chayul Chu in Tibet) is a trans- Himalayan river and a tributary of the Brahmaputra River that flows through Tibet's Lhuntse County in the Shannan Prefecture in Southwestern China, and the Indian states of Arunachal Pradesh and A ...

opened after an interval of 8 days and the wave, high, submerged several villages and killed 532 people. The shock was more damaging in Assam, in terms of property loss, than the earthquake of 1897. In addition to the extreme shaking, there were floods when the rivers rose high after the earthquake bringing down sand, mud, trees, and all kinds of debris. Pilots flying over the meizoseismal area reported great changes in topography. This was largely due to enormous landslides, some of which were photographed. In Tibet, Heinrich Harrer reported strong shaking in

Lhasa Lhasa, officially the Chengguan District of Lhasa City, is the inner urban district of Lhasa (city), Lhasa City, Tibet Autonomous Region, Southwestern China. Lhasa is the second most populous urban area on the Tibetan Plateau after Xining ...

and loud cracking noises from the earth. Aftershocks were felt in Lhasa for days. In Rima, Tibet (modern-day Zayü Town), Frank Kingdon-Ward, noted violent shaking, extensive slides, and the rise of the streams. Helen Myers Morse, an American missionary living in Putao, northern

Burma Myanmar, officially the Republic of the Union of Myanmar; and also referred to as Burma (the official English name until 1989), is a country in northwest Southeast Asia. It is the largest country by area in Mainland Southeast Asia and ha ...

at the time, wrote letters home describing the main shake, the numerous aftershocks, and of the noise coming out of the earth. One of the more westerly aftershocks, a few days later, was felt more extensively in Assam than the main shock. This led certain journalists to the belief that the later shock was 'bigger' and must be the greatest earthquake of all time. This is a typical example of the confusion between the essential concepts of magnitude and intensity. The extraordinary sounds heard by Kingdon-Ward and many others at the times of the main earthquake have been specially investigated.

Seiche A seiche ( ) is a standing wave in an enclosed or partially enclosed body of water. Seiches and seiche-related phenomena have been observed on lakes, reservoirs, swimming pools, bays, harbors, caves, and seas. The key requirement for formatio ...

s were observed as far away as Norway and England. (p. 63–64.)

Future threat

An article in ''

Science Science is a systematic discipline that builds and organises knowledge in the form of testable hypotheses and predictions about the universe. Modern science is typically divided into twoor threemajor branches: the natural sciences, which stu ...

'', published in response to the 2001 Bhuj earthquake, calculated that 70 percent of the

Himalayas The Himalayas, or Himalaya ( ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the Earth's highest peaks, including the highest, Mount Everest. More than list of h ...

could experience an extremely powerful earthquake. The prediction came from research of the historical records from the area as well as the presumption that since the 1950 Medog earthquake enough slippage has taken place for a large earthquake to occur. In 2015, the Himalayas were hit by a 7.8-magnitude earthquake with an epicenter further west in Nepal.

References

External links

At Khowang
– A photo by Dhaniram Bora * {{DEFAULTSORT:Assam 1950 in India 1950 in China 1950s in Tibet 1950 earthquakes 1950s in Assam August 1950 in Asia 1950 Assam 1950 Assam 1950 Assam Earthquakes in Myanmar 1950 in Nepal 1950 disasters in China 1950 disasters in India