1950 Assam–Tibet earthquake

1950 earthquake centered on border between Tibet, China and Assam, India

The earthquake occurred in the rugged mountainous areas between the Himalayas and the Hengduan Mountains. The earthquake was located just south of the McMahon Line between India and Tibet, and had devastating effects in both regions. This great earthquake has a calculated magnitude of 8.7 and is regarded as one of the most important since the introduction of seismological observing stations. It was the sixth largest earthquake of the 20th century. It is also the largest known earthquake to have not been caused by an oceanic subduction. Instead, this quake was caused by two continental plates colliding. Aftershocks were numerous; many of them were of magnitude 6 and over and well enough recorded at distant stations for reasonably good epicentre location. From such data the Indian Seismological Service established an enormous geographical spread of this activity, from about 90 deg to 97 deg east longitude, with the epicentre of the great earthquake near the eastern margin.

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, 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.)

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.