Bangkok reviews construction safety after a high-rise was crumpled by an earthquake 800 miles away

“I think we need to find the root cause so at least we can learn some lessons and improve building regulations," Chadchart said. “In the end, we will have some results that will improve safety in Bangkok.”

Shares in the property developer handling the project, Italian Thai Development, fell 27% in trading Monday as questions were raised about the building's design, enforcement of construction safety codes, and the state-run Chinese contractor building the State Audit Office.

The construction company, a subsidiary of state-run China Railway No. 10 Engineering Group, last year posted a video online celebrating the 137-meter-tall (about 450 foot) structure's topping out, showing plenty of drone footage and boasting about the quality of the design, construction and management of the project.

Interior Minister Anutin Charnvirakul, whose family owns one of Thailand’s largest construction conglomerates, told reporters he has ordered an investigation committee to be set up and to report the results back to him within seven days. He pointed to three possible factors behind the collapse: the designer, the inspectors or the builders.

“We will definitely find the true reasons as to why this building has collapsed, because it’s all scientific,” Anutin said.

While not on a geologic fault, Bangkok is built on relatively unstable alluvial soil, on the banks of the Chao Phraya River. That can amplify ground motion for tall buildings. The city has long been sinking under the weight of its skyscrapers, leading authorities to restrict the use of groundwater to help reduce subsidence.

Friday's earthquake gave the Thai capital an unusually long and strong jolt, causing water from rooftop pools to cascade down skyscrapers, light-rail trains to rock on their tracks, and millions of people to flee homes and offices. People waited for hours outside in the blazing midday heat for buildings to undergo safety checks. A warning of aftershocks Monday caused a brief panic, with some people again heading to the streets.

Questions about enforcement of safety and quality standards in Bangkok were raised earlier by the collapse of parts of a highway under construction in the city’s outskirts that killed several construction workers. One potential concern was the quality of the steel rods embedded in concrete slabs and pillars to reinforce them.

Most other damage in the city appeared to be superficial, such as fallen ceiling panels and fittings and cracked plaster, and mainly in relatively newer buildings put up by private developers.

Chadchart said building owners need to inspect their properties to determine whether any cracks were old or new. The Thailand Structural Engineers Association was recruiting volunteers to help with inspections. Recently, it urged a review of all large-scale projects in the city.

Most buildings in Bangkok were built before the government revised construction standards to require meet earthquake safety requirements, said Christian Malaga-Chuquitaype, a lecturer in civil and environmental engineering at the Imperial College in London.

Many structures are constructed without beams using “flat slabs” and slender columns, which maximizes open floor space and minimizes costs, he noted. The company building the State Audit Office boasted in its video that it used a beamless design.

“While this design has cost and architectural advantages, it performs poorly during earthquakes, often failing in a brittle and sudden (almost explosive) manner,” he wrote in an analysis. "A thorough forensic analysis is needed, but this building type is no longer recommended in earthquake-prone areas.” ___

Associated Press writers David Rising and Grant Peck contributed to this report.