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Few buildings constructed to withstand temblors

High-rise buildings in Bangkok could fall like dominoes if the capital is shaken by a major earthquake, even from a distant fault line, a group of seismic experts has warned.

And they urged authorities to better educate people on how to handle the situation if and when a quake occurs.

Because Bangkok is not located within the Pacific's so-called "Ring of Fire", many tall buildings are particularly vulnerable to jolts as most of them were not built to withstand major tremors.

"There is a likelihood an earthquake outside Bangkok could affect the city," said Pran Siamwalla, an independent academic on environment.

"These quakes could be caused by two fault lines - one in the Andaman Sea, about 700km west of Bangkok, and the Si Sawat line 200km away in Kanchanaburi province."

Mr Pran and his team held a workshop last week about the possibilities of the capital being hit by distant large earthquakes. He hoped it would be a driver for the authorities to identify strategic action and implementation of risk reduction systems.

Mr Phan said Bangkok should use Mexico City as a model to design its reaction plan as both cities have similar soil layers. Mexico City also lies within the Trans-Mexican Volcanic Belt, which is known as the Sierra Nevada.

"Bangkok's soil is made up primarily of delta mud. If an earthquake happens in a location away from the city, its effect on Bangkok could be amplified by three to five times through underground ripples," said Mr Pran.

He said if an earthquake of magnitude 8 occurred along the Si Sawat fault line, it could cause the Sri Nakharin dam in Kanchanaburi to burst sending a huge wave along its path more intense than a tsunami.

In 1985, an earthquake with an epicentre 400km from Mexico City caused 30% of the buildings to collapse.

Mr Pran said many scientists believe the 6-20th floors of tall buildings will bear the heaviest brunt from a quake.

"But the roads and tollways might not collapse. The quake might only affect high-rise buildings," he added.

Mr Phan said that although Bangkok is at risk of an earthquake, city authorities can take preventative measures against major loss of life and property.

In the past four years, the Bangkok Metropolitan Administration has changed some city codes on building construction, but they are not yet fully implemented.

"Most engineers still rely on old statistics from 20 years ago to calculate a building's resistance to earthquakes while [we know] there are more quakes at present," said Mr Pran.

Old buildings will need structural modification to make them quake resistant, and this will incur costs of about 5-15% of the construction budget.

The government can help by offering property tax reduction for owners to retrofit their old buildings.

Mr Pran said he plans to hold another meeting soon with the BMA, the Information, Communication and Technology Ministry and the National Disaster Warning Centre to develop a roadmap and action plan for quake resistance measures for buildings.