By Our Staff Reporter
Guwahati, April 28: Northeast India is located in the highest earthquake prone zone V. In this region, earthquake comes with landslides, floods and a series of smaller magnitude tremors. Here earthquakes of intensity up to 9 on the Richter scale can be expected.
Two of the most catastrophic earthquakes in the world visited this region in 1897 and 1950. Old-timers still shudder when reminiscing the ‘big one’ which nearly turned Assam upside down on Independence Day in 1950. As for the equally massive 1897 earthquake, the dramatic accounts of violent upthrow continue to remain entrenched in popular memory in the region.
According to a hazard map by the Global Seismic Hazard Assessment Programme, Assam can expect to have a peak gravitatiol acceleration (PGA) of 0.24 g to 0.48 g. The region where the highest PGA can be expected is along the State’s border with Meghalaya, the site of the Great Indian earthquake of 1897. The 1897 earthquake centered at Sangsik in Meghalaya was felt over 6,50,000 square kilometres. There was heavy damage to the towns of Cherrapunji, Shillong, Silchar and Sylhet and also in Manipur. This 8.7 magnitude quake was one of the most powerful to shake the Indian subcontinent and probably one of the largest known anywhere. The quake wreaked havoc across south-west of the present states of Assam, Meghalaya and Bangladesh. 1,542 people were killed and hundreds more hurt. Damage from the earthquake extended into Kolkata and Dhaka where dozens of buildings were badly damaged or partially collapsed. Shaking from the event was felt across India, as far as Ahmedabad and Peshawar.
This quake caused great destruction to many towns in Assam and Meghalaya. The damage to Shillong finds wide mention, where most of the structures like the Telegraph House along with churches, stone houses and bridges were flattened.
Landslides were reported all across the Garo Hills. The towns of Dhubri, Goalpara, Guwahati and Cooch Behar in Assam and West Bengal suffered much devastation.
Earthquake fountains, some 4 feet high, were reported from Dhubri. The Jolboda and Krishi bridges were destroyed.
At Goalpara, a 10-foot wave from the Bramaputra (possibly due to subsidence), swept into the area, destroying the bazaar and many pukka buildings. Ground waves were reported from lbari, where the observer saw entire rice fields rise and fall as the waves passed under them. At Guwahati, the earth subsided along the Bramaputra and several sand vents were formed. The Bramaputra is also reported to have risen by 7.6 metres and even reversed its flow during the colossal shock. Powerful aftershocks continued to rock the region at least for a week.
A quake of magnitude 7 rocked Dhubri on July 2, 1930. Most of the buildings in Dhubri and the surrounding areas were destroyed in this shock. It was felt as far away as Kolkata, Chittagong, Dibrugarh, and Pat. This quake was followed by six major aftershocks of magnitude 6. The first three were in the immediate epicentral region south of Dhubri.
The earthquake of 29th July, 1947, had a magnitude of 7.7. This quake was felt over a larger region - Assam, Bengal (upto Kolkata) and Bihar (upto Purnea). At Jorhat, rivers overflowed their banks. At Dibrugarh, Jorhat and Tezpur, numerous houses developed cracks in walls while Guwahati witnessed complete power breakdown.
This was followed by the cataclysmic earthquake on 15 August, 1950, at 7.39 pm in the evening. Striking the mountainous region along India’s border with Chi, the 8.7 magnitude quake violently shook the entire Northeast and many parts of Eastern India, with the effect felt throughout Bangladesh, Bhutan and Myanmar. Damage occurred in the entire region as far as Kolkata. Lakhimpur, Sadiya, Sibsagar, Dibrugarh and Saikoaghat bore the brunt, and 1,526 deaths were recorded.
There was widespread devastation in Upper Assam, with huge landslides in the mountains and destruction of entire forests. Landslips dammed up tributaries of the Bramaputra, including the Dihang, Dihing and Subansiri. When these dams were breached a few days later, they caused extensive flooding in the lower reaches.
Huge fissures opened on the earth, from which water and sand spouts were emitted high, while trees were swallowed up whole. The earthquake was followed by a large number of aftershocks, most of which were of magnitude 6.0 or greater.
The great 1950 quake caused major changes in topography and alterations of relief in the affected regions, permanently changing the flow patterns of several rivers.
In 1984, 20 persons were killed and 100 injured in Cachar district in a magnitude 6 quake centred at Silchar. This quake was “forecast” on the basis of a seismic swarm which was followed by a period of quiescence. An area of about 250 sq km was affected.
Four years later, another quake of 7.3 magnitude occurred on the Indo-Burma border.
Its hypocentre was at a depth of 91km. Widespread damage was recorded at Jorhat, Golaghat, Dirugarh and Manipur. However, because of its occurrence at a considerable depth, the effect was comparatively low. (Source: Centre for tural Disaster Magement)