1950 Assam–Tibet earthquake

(Redirected from Assam earthquake of 1950) 1950 earthquake centered on border between Tibet, China and Assam, India

1950 Assam–Tibet earthquake

UTC time	1950-08-15 14:09:34
ISC event	895681
USGS-ANSS	ComCat
Local date	August 15, 1950 (1950-08-15)
Local time	19:39:34 IST
Magnitude	8.7 M_w
Depth	15 km (9.3 mi)
Epicenter	28°22′N 96°27′E / 28.36°N 96.45°E / 28.36; 96.45
Fault	Main Himalayan Thrust
Type	Oblique-slip
Areas affected	Assam, India Tibet, China
Max. intensity	MMI XI (Extreme)
Casualties	4,800

Main faults of the Himalayas/Tibetan Plateau

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, the earthquake was destructive in both Assam (India) and Tibet (China), and approximately 4,800 people were killed. The earthquake is notable as being the largest recorded quake caused by continental collision rather than subduction, 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 between the northward moving Indian plate and Eurasia. 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 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 Sagaing Fault that together bound the Burma Microplate.

Past seismicity

In an attempt to further uncover the seismic history of Northeast India, field studies were conducted by scientists with the National Geophysical Research Institute and Institute of Physics, Bhubaneswar. The study discovered signs of soil liquefaction including sills and sand volcanoes inside at least twelve trenches in alluvial fans and on the Burhi Dihing River Valley that were formed by past seismic activity. Radiocarbon dating 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 Fault. Magnitudes calculated for the earthquake range from M_w  8.6–8.8. making it the largest onshore earthquake ever recorded and the largest not associated with subduction. It was the sixth largest earthquake of the 20th century.

Aftershocks were numerous; many of them were of magnitude 6 and over and well enough recorded at distant stations for reasonably good epicentre location. The aftershock epicenters covered a very large area over the Abor and Mishmi hills of about 30,000 km, 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 was discovered at multiple locations along the trace of the Abor Hills section of the Main Frontal Thrust and along the Mishmi Thrust. The total observed surface rupture length along both faults is ≥ 200 km.

Published focal mechanisms 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 Mishmi Thrust. This combined source provides a good fit with observations of seismic arrivals. The observed slip on the Mishmi Thrust is 34 ± 2.5 m. Combined with the estimated rupture area 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. In the Dibang Valley, a landslide lake burst without causing damage, but another at Subansiri River opened after an interval of 8 days and the wave, 7 m (23 ft) 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 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 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. Seiches were observed as far away as Norway and England. (p. 63–64.)

Future threat

An article in Science, published in response to the 2001 Bhuj earthquake, calculated that 70 percent of the Himalayas 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

^ ISC (2022), ISC-GEM Global Instrumental Earthquake Catalogue (1904–2018), Version 9.1, International Seismological Centre
"M8.6 – eastern Xizang-India border region". United States Geological Survey.
PAGER-CAT Earthquake Catalog, Version 2008_06.1, United States Geological Survey, September 4, 2009
^ "Historic Earthquakes, Assam – Tibet". United States Geological Survey. Archived from the original on November 10, 2016. Retrieved January 24, 2012.
^ Coudurier-Curveur, A.; Tapponier, P.; Okal, E.; Van der Woerd, J.; Kali, E.; Choudhury, S.; Baruah, S.; Etchebes, M.; Karakaş, Ç. (2020). "A composite rupture model for the great 1950 Assam earthquake across the cusp of the East Himalayan Syntaxis". Earth and Planetary Science Letters. 531. doi:10.1016/j.epsl.2019.115928. hdl:10356/136999.
Reddy, D.V.; Nagabhushanam, P.; et al. (September 2009). "The great 1950 Assam Earthquake revisited: Field evidences of liquefaction and search for paleoseismic events". Tectonophysics. 474 (3): 463–472. Bibcode:2009Tectp.474..463R. doi:10.1016/j.tecto.2009.04.024.
"Largest Earthquakes in the World Since 1900". United States Geological Survey. September 20, 2011. Archived from the original on 7 November 2010. Retrieved December 17, 2010.
"Significant Earthquake INDIA-CHINA". National Geophysical Data Center. Retrieved February 14, 2022.
He, X.; Wu, J.; Wang, C.; Ye, M. (2018). "Historical Earthquakes and Their Socioeconomic Consequences in China: 1950–2017". International Journal of Environmental Research and Public Health. 15 (2728): 2728. doi:10.3390/ijerph15122728. PMID 30513946.
Harrer, Heinrich (1953). Seven Years in Tibet. Putnam.
Kingdon-Ward, F. (1953). "The Assam Earthquake of 1950". The Geographical Journal. 119 (2): 169–182. Bibcode:1953GeogJ.119..169K. doi:10.2307/1791200. JSTOR 1791200.
Myers Morse, Helen (2003). Once I Was Young. Terre Haute, Indiana. pp. 167–171.{{cite book}}: CS1 maint: location missing publisher (link)
"Quake in Himalayas: US & Indian experts differ". The Statesman. September 6, 2001.

External links

At Khowang – A photo by Dhaniram Bora
The International Seismological Centre has a bibliography and/or authoritative data for this event.

v t e Earthquakes in China
Historical	1038 Dingxiang 1290 Chihli (Inner Mongolia) 1303 Hongdong, Shanxi 1536 Xichang, Sichuan 1556 Shaanxi 1604 Quanzhou, Fujian 1605 Guangdong 1626 Lingqiu, Shanxi 1654 Tianshui, Gansu 1668 Tangcheng, Shandong 1679 Beijing, Hebei 1695 Linfen, Shanxi 1709 Zhongwei 1718 Tongwei, Gansu 1733 Dongchuan, Yunnan 1738 Dangjiang, Qinghai 1739 Yinchuan–Pingluo, Ningxia 1786 Kangding-Luding, Sichuan 1815 Pinglu, Shanxi 1830 Cixian, Hebei 1833 Kunming, Yunnan 1850 Xichang, Sichuan 1879 Wudu, Gansu 1889 Chilik, Xinjiang
20th century	1902 Kashgar, Xinjiang 1906 Manas, Xinjiang 1913 Eshan, Yunnan 1918 Shantou, Guangdong 1920 Haiyuan, Ningxia 1923 Renda, Sichuan 1925 Dali, Yunnan 1927 Gulang, Gansu 1931 Fuyun, Xinjiang 1932 Changma 1933 Diexi, Sichuan 1936 Lingshan, Guangxi 1937 Heze, Shandong 1947 Assam 1948 Litang, Sichuan 1950 Assam–Tibet 1952 Damxung 1955 Kangding, Sichuan 1955 Yuzha, Sichuan 1966 Xingtai, Hebei 1969 Bohai Sea 1969 Yangjiang, Guangdong 1970 Tonghai, Yunnan 1973 Luhuo, Sichuan 1974 Zhaotong, Yunnan 1975 Haicheng, Liaoning 1976 Longling, Yunnan 1976 Tangshan, Hebei 1976 Songpan–Pingwu, Sichuan 1981 Dawu, Sichuan 1983 Heze, Shandong 1985 Luquan, Yunnan 1985 Wuqia, Xinjiang 1988 Lancang–Gengma, Yunnan 1990 Gonghe, Qinghai 1994 Taiwan Strait 1995 Menglian, Yunnan 1995 Wuding, Yunnan 1996 Lijiang, Yunnan 1996 Baotou, Inner Mongolia 1997 Jiashi, Xinjiang 1997 Manyi, Tibet 1998 Zhangbei 1998 Ninglang, Yunnan 2000 Yunnan
21st century	2001 Kunlun 2003 Bachu, Xinjiang 2003 Dayao 2003 Zhaosu, Xinjiang 2005 Ruichang, Jiangxi 2006 Yanjin, Yunnan 2008 Sichuan 2008 Yingjiang, Yunnan 2008 Panzhihua, Sichuan 2008 Damxung, Tibet 2009 Xinjiang 2009 Yunnan 2010 Yushu, Qinghai 2011 Yunnan 2011 Myanmar 2012 Yangzhou, Jiangsu 2012 Zhaotong, Yunnan 2013 Lushan, Sichuan 2013 Dingxi, Gansu 2014 Yutian, Xinjiang 2014 Yingjiang, Yunnan 2014 Ludian, Yunnan 2014 Jinggu, Yunnan 2014 Kangding, Sichuan 2015 Pishan, Xinjiang 2017 Taxkorgan, Xinjiang 2017 Jiuzhaigou, Sichuan 2017 Jinghe, Xinjiang 2019 Changning, Sichuan 2020 Kashgar, Xinjiang 2020 Qiaojia, Yunnan 2021 Dali, Yunnan 2021 Maduo, Qinghai 2021 Luxian, Sichuan 2022 Menyuan, Qinghai 2022 Ya'an, Sichuan 2022 Luding, Sichuan 2023 Jishishan 2024 Uqturpan
By province	Sichuan Yunnan
Organizations	China Meteorological Administration China Earthquake Administration China Earthquake Networks Center China Geological Survey China International Search and Rescue Team

v t e Earthquakes in India
Historical	1505 Lo Mustang 1555 Kashmir 1803 Garhwal 1819 Rann of Kutch 1833 Kathmandu–Bihar 1869 Cachar 1881 Nicobar Islands 1885 Kashmir 1897 Assam
20th century	1905 Kangra 1930 Dhubri 1934 Nepal–India 1935 Quetta 1941 Andaman Islands 1947 Assam 1950 Assam–Tibet 1956 Anjar 1967 Koynanagar 1975 Kinnaur 1980 Pithoragarh 1984 Cachar 1988 Myanmar–India 1988 Nepal 1991 Uttarkashi 1993 Latur 1997 Jabalpur 1997 Chittagong 1999 Chamoli
21st century	2001 Gujarat 2004 Indian Ocean 2005 Kashmir 2009 Andaman Islands 2011 Sikkim April 2015 Nepal May 2015 Nepal October 2015 Hindu Kush 2016 Imphal 2016 Kani 2016 Chauk 2017 Tripura 2021 Assam 2022 Nepal 2023 Badakhshan 2023 Nepal
Related topics	Earthquake zones of India Geology of the Himalayas

v t e Earthquakes and plate tectonics in Myanmar
Pre-20th century	1762 Rahkine 1839 Innwa 1858 Prome
20th century	1912 Taunggyi 1930 Bago 1930 Pyu 1931 Myitkyina 1946 Sagaing 1950 Assam–Tibet 1956 Sagaing 1975 Bagan 1976 Yunnan 1988 Myanmar–India 1988 Lancang–Gengma 1995 Menglian 1997 Chittagong
21st century	2003 Taungdwingyi 2004 Indian Ocean 2009 Coco Islands 2011 Yingjiang 2011 Tarlay 2012 Thabeikkyin 2016 Imphal 2016 Chauk 2016 Kani
Fault zones and tectonic plates	Sagaing Fault Kyaukkyan Fault Three Pagodas Fault West Andaman Fault Kabaw Fault Sunda megathrust Main Himalayan Thrust Main Frontal Thrust Burma plate Sunda plate Indian plate Eurasian plate

v t e Himalayan earthquakes
Notable Himalayan quakes	1505 Lo Mustang 1555 Kashmir 1714 Bhutan 1803 Garhwal 1833 Kathmandu–Bihar 1885 Kashmir 1897 Assam 1905 Kangra 1934 Bihar 1947 Assam 1950 Assam–Tibet 1980 Nepal 1988 Myanmar-India 1988 Nepal 1991 Uttarkashi 1999 Chamoli 2005 Kashmir 2008 Damxung 2009 Bhutan 2011 Sikkim April 2015 Nepal May 2015 Nepal 2021 Assam 2023 Nepal
Plate tectonics	Geology of the Himalayas Indian plate Eurasian plate Oldham Fault Main Frontal Thrust Main Himalayan Thrust Main Central Thrust South Tibetan Detachment North Himalayan Normal Fault

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