Oct. 2 (Bloomberg) -- Thousands may be trapped in collapsed structures in Indonesia’s Padang city following this week’s earthquake because builders didn’t follow construction laws, one of the country’s top structural engineers said.

“It seems that the columns were very weak, very thin and carrying heavy loads,” Adang Surahman, chairman of the Indonesian Earthquake Engineering Association, said by telephone. “I don’t believe they were complying with our building codes.”

While Indonesia has “sound” building regulations, they’re only applied properly in the capital of Jakarta and surrounding areas, he said. The damage caused by the 7.6-magnitude quake on Sept. 30 underscores the challenge of enforcing such regulations outside of affluent urban areas, he added.

Thousands of people may be under fallen houses in Padang and at least 1,100 people were killed in the temblor, John Holmes, the United Nations humanitarian chief, told a press briefing in New York yesterday. At least 500 buildings collapsed, including homes, schools, mosques, and shops, he said. Indonesia today reduced its death toll from the earthquake on Sumatra island to 467 from 770, as rescuers raced to find survivors.

Indonesia has suffered more deaths from natural disasters in the past 30 years than any other country besides Ethiopia and Bangladesh, according to data compiled by Belgium’s Universite Catholique de Louvain. The country of 17,500 islands forms part of the “Ring of Fire,” an arc of volcanoes and fault lines surrounding the Pacific Basin.

A team of engineers from the association will head to Padang, West Sumatra’s largest city, as early as today to start inspecting the damage, Suraham said. Middle-income people sometimes suffer the most from poorly constructed dwellings because they can afford concrete, he said.

‘Wooden Houses’

“The poor live in wooden houses which are less vulnerable and high-rise buildings are OK in general,” he said.

In Air Pacah, a suburb about 10 minutes by car from Padang’s city center, residents were trying last night to salvage whatever what they could from collapsed shops. A rescue worker said hundreds of people trapped inside were probably dead.

“If they could follow an appropriate design code, things wouldn’t be this serious,” said Kazuo Konagai, an earthquake engineering specialist at the University of Tokyo who has led research teams to Padang. Many structures in the area aren’t built to withstand large tremors or big waves, he said.

Preventing illegal construction is key to boosting earthquake safety, according to a 2006 report from the Joint Committee of Indonesia and Japan on Disaster Reduction. The government should help provide incentives to comply with building codes, including preferential housing loans for legal structures, the report said.

Existing Homes

“The biggest problem of all is the existing stock of housing,” said Paul Grundy, a civil engineering professor at Austalia’s Monash University. “The costs of retrofitting the entire country with resistant housing is enormous, and it only happens if you have the community demand for it.”

An even bigger temblor near Padang may occur between now and 2040 because of a “failure sequence” on a fault line off Sumatra, said Kerry Sieh, director of the Earth Observatory of Singapore. Such a quake may measure as large as 8.8 magnitude, he said.

“Given that hundreds of buildings have collapsed in Padang from a 7.6, what will happen when the 8.8 happens?” Sieh said. “It’s as if construction practices haven’t changed in spite of this warning.”

To contact the reporter on this story: Daniel Ten Kate in Bangkok at dtenkate@bloomberg.net

Last Updated: October 2, 2009 03:26 EDT