Earthquake News

M 8.6 - 1950 Assam-Tibet Earthquake

It has been 70 years since the Assam-Tibet 8.6-magnitude earthquake.

In the Nyingchi-Qamdo-Zhamo (Rima, Zayu) region of eastern Tibet, at least 780 people were killed and several structures were destroyed. Large landslides, ground fractures, and sand blasts happened nearby. Yedong, a settlement in the Medog region, washed away when it sank into the Yarlung Zangbo (Brahmaputra) River. Lhasa, as well as the Chinese provinces of Sichuan and Yunnan, felt the earthquake.

Additionally, the hills surrounding the Sibsagar-Sadiya region of Assam, India, sustained severe damage (X). In the Abor Hills, almost 70 settlements were destroyed, largely by landslides. The Subansiri River was blocked by huge landslides. A 7 m (23 ft) high tsunami that was caused by the natural dam breaking eight days later swamped many communities and claimed the lives of 536 people.

As far away as Calcutta, the earthquake was felt (VI). Seiches have been spotted in numerous Norwegian lakes and fjords, as well as at least three English reservoirs. Despite the fact that the majority of sources identify the epicenter in Tibet, many still refer to this earthquake as the Assam-Tibet or even the Assam earthquake. Therefore, it's probable that both the number of fatalities from the Subansiri River flood and those related to Tibet are underestimated. Additionally, Gu et al. do not provide casualty totals for Yedong or other regions of Tibet that sustained the most significant devastation. The actual death toll may therefore be significantly higher than the estimate.

At Sadya, Passighat, Dum Dum, Dibrugarh, North Lakhimpur, and Sibsagar the intensity scale is X; at Digboi and Galaghat it is IX; at Tezpur, Ganhati, and Shillong it is VIII; and at Daca, Calcutta Dhubri, Darjeeling, and Imphal it is VI. 49,700 sq km of the 1,794,000 sq km macroseismic area sustained significant damage.

Strasbourg considers this large earthquake, which caused destruction in Assam and Tibet and had a computed magnitude of 8.6, to be the most significant one since the establishment of seismological observing stations. Numerous rockfalls in the Mishmi Hills and the ensuing clearing of wooded areas changed the relief. Landslides caused the destruction of 70 settlements and the deaths of 156 people in the Arbor Hills. Dykes prevented the Brahmaputra's tributaries from flowing; in the Dibang valley, one broke without causing any damage, but in Subansiri, another opened after an interval of 8 days, generating a wave that was 7 meters high and inundated numerous villages, killing 532 people.

A total of 2000 houses, mosques, and temples were destroyed. The Brahmaputra Basin in NE India has been the most severely affected.

Taken from Seismological Notes, the American Seismological Society's journal. Each issue of the BSSA has "Seismological Notes," a list of recent significant earthquakes with brief summaries.
Since the epicenter occurred close to Rima, a territory that both China and Tibet claim, this earthquake was technically not in India. It is one of the few earthquakes whose magnitude, 8.7, was determined by instruments. In terms of property damage, this shock was more detrimental in Assam than the earthquake of 1897. The consequences of flooding were compounded to those of shaking; following the earthquake, the rivers rose high, bringing down sand, mud, trees, and several other types of debris.

Pilots flying above the meizoseismal region noted significant topographic changes, which were mostly caused by massive slides, some of which were captured on camera.

F's account is the only one that is accessible right now. Kingdon-Ward, a botanist who visited Rima. He confirms Rima's intense shaking, the area's huge slides, and the increase of the streams, but he didn't have much time to observe; instead, he was forced to focus on the challenges of leaving and returning to India. There were many aftershocks, many of which were at least magnitude 6 and well-enough documented at distant sites to allow for a reasonably accurate epicenter position. With the large earthquake's epicenter located close to the eastern boundary, Dr. Tandon of the Indian Seismological Service was able to determine the enormous geographic spread of this activity from roughly 90 degrees to 97 degrees east longitude.

A few days later, one of the stronger aftershocks to the west was felt more strongly in Assam than in the mainshock. This led some journalists to the ridiculous conclusion that the latter shock must have been the biggest earthquake ever because it was "larger." This is an illustration of how the fundamental ideas of scale and intensity are frequently misunderstood. Special attention has been paid to the strange noises that Kingdon-Ward and many other people reported hearing during the major earthquake. Even in England and Norway, seiches were spotted.

Kingdon-Ward, who lived close to the epicentre of the 1950 great earthquake in Tibet, reported loud explosions that seemed to be coming from a great height after the shock. Over 750 miles away, at numerous locations in India and Burma, these sounds were audible.

Source: USGS

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