Expert warns of 'preludes' to quake disaster

Bangladesh could be teetering on the verge of an earthquake disaster with two abutting tectonic plates heading for a clash, with high risk too of being inundated by a tidal wave, after a major 7.8 quake off the Andamans in the Indian Ocean triggered a tsunami alert this week and a subsequent medium 5.6 tremor jolted northern districts.

"Bangladesh is an earthquake prone area due to her geological and tectonic structures, especially Sylhet, Chittagong and Chittagong Hill Tract areas," geology professor Syed Humayun Akhter told bdnews24.com on Thursday.

The northern region of Bangladesh lies above the seam of the Indian and Eurasian tectonic plates and the eastern part is above the joint of the Burmese and Indian plates.

The Indian plate is edging north-east while the Burmese plate is moving north-west, say experts.

Besides, the country is perched on three faults and a seismic gap.

If an earthquake of more than 8 on the Richter scale occurs in Bangladesh or in India's Meghalaya, Assam, Manipur, Mizoram or in Myanmar the trail of damage will be colossal, said Akhter.

The most at-risk areas in Bangladesh are over the Tangail-Modhupur fault, Sylhet's Dauki fault, Sitakundu-Teknaf fault

Another major concern is the north-Andaman-Teknaf subduction zone, or seismic gap.

Tsunami risk

"A seismic gap of 600 kilometres in the Bay of Bengal from north Andaman to Teknaf contains enough energy to cause an earthquake measuring over 7.5 in the Richter scale," said Prof Akhter, also in charge of the Earth Observatory at Dhaka University.

The Indian Ocean quake on Tuesday, Aug 11, occurred in the Andaman-Teknaf subduction zone.

"It shows the subduction zone is active and could generate a devastating tsunami in the near future," said Akhter.

On Dec 26, 2004, a massive underwater quake measuring 9.3 caused a huge tidal wave or tsunami in the western Bay of Bengal. It was the second biggest earthquake recorded in the region and was caused by friction between the Indian and Burmese plates.

Bangladesh was safe during the 2004 tsunami because the direction of the friction was north-south giving rise to a east-west moving wave.

But the fracture of the Teknaf-Andaman seismic gap is along a north-east to south-west direction.

If a tsunami is generated in the Bay of Bengal from this subduction zone, it will directly assail the coastal areas including Barisal, Patuakhali, Noakhali, Cox's Bazar and Snadwip and India's Orissa, West Bengal, said Akhter.

"Our coast is only 750 km away from Teknaf-Andaman seismic gap. A tsunami generated there will take only one hour to reach the coast and the impact will be colossal because of the low plain lands of Bangladesh," he said.

'Preludes to serious quake'

A few hundred minor earthquakes in different parts of the country in recent years can also be seen as preludes to a serious one, said Akhter.

The earthquake on Dec 20, 2000, near capital Dhaka indicated that a major earthquake is on its way, he said, adding that unplanned urbanisation in Dhaka and other cities would lead to catastrophic loss of life.

"Around a dozen quakes recorded at the Modhupur fault in September last year are also deemed as foreshocks of a major quake," said Akhter.

"The devastating earthquakes in Pakistan and Sumatra over the last few years are a warning bell for us too," said Akhter.

Besides mountainous areas, there are many faults in plain lands too, he said.

"Most areas of the country consist of low plain lands and soft silt. If a major earthquake occurs the disaster will be a calamitous liquefaction," he said.

Roger Bilham, geology professor at the Colorado University of USA, has also confirmed seismic gaps in a number of places at the foot of the Himalayas and predicted several earthquakes measuring 7 and 8 Richter scale in the region in the near future.

Clashes have been more frequent in recent times between the Indian and Eurasian plates and the Burmese and Indian plates.

The Indian plate lies under Bangladesh, India, Pakistan, the Arabian Sea and the Bay of Bengal. Bangladesh is located at a joint of a part of the Indian plate and three other plates in the north-east.

The first earthquake to be properly recorded in Bangladesh was in 1548.

A major quake struck the Chittagong-Burma coast in 1762 that caused a number of islands to sink into the Bay of Bengal and sprouted two mud-volcanoes at Sitakundu Hill and Teknaf that rose 1.5 to 2 metres above the sea level.

"Probably, the 1762 earthquake was the first recorded underwater quake in this region giving rise to a tsunami," said Akhter.

Bangladesh has seen six earthquakes measuring 7 or more on the Richter scale since records began, in Sylhet, Srimangal, Manikganj and Chittagong.

Generally an earthquake below 5 in magnitude occurs every one and a half years. A major earthquake occurs after 100 years.

"An earthquake is hard to forecast like any other natural disasters. But we can minimise the impact by increasing awareness," he said.

The overall preparation of the earthquake can be divided into three parts – pre-quake preparation, preparation during the quake and post-quake preparation.

Akhter suggested preparing seismotectonic maps to earmark earthquake prone areas, collecting data on regular tremors and upgrading the national building code.

Training on earthquake preparedness in schools and rehearsals on self-defence will also be useful, he said.

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