Quelling the tremors of March 28

While the recent earthquake caused limited damage, it heightened public awareness of the potential for natural disasters

- KANANA KATHARANGSIPORN

The earthquake that struck Myanmar on March 28 sent tremors through many high-rise buildings in Bangkok, shaking not just the structures but also buyer confidence, if only briefly.

While many question the safety of living in vertical structures, homebuyers have become more cautious, scrutinising each project's safety standards, contractor reputation and long-term reliability more closely.

WHY DID THE MYANMAR EARTHQUAKE SHAKE BUILDINGS MORE THAN 1,300 KILOMETRES AWAY IN BANGKOK?

Prof Pennung Warnitchai, chair of the structural engineering programme at the Asian Institute of Technology, said the tremors were caused by Bangkok's deep, soft soil basin, which extends as far as 800 metres below the surface.

"Bangkok lies at the bottom of a soft-soil basin, much like the bottom of a frying pan," he said. "The rim of this geological pan stretches to Chachoengsao, Nakhon Nayok and Ayutthaya, forming a unique bowl of soft soil."

This type of soil can significantly amplify long-period, low-frequency seismic waves from distant earthquakes by as much as 3-4 times, as they pass through the basin, said Prof Pennung.

When such waves hit Bangkok, they can trigger a resonance effect in high-rise buildings, particularly those that have a natural sway frequency aligned with that of the seismic waves.

For example, 50-storey buildings typically have a natural vibration period of about 5 seconds, while buildings with 20 to 40 storeys range from 2-4 seconds, matching the wave period and intensifying the swaying motion.

These buildings are especially affected, which aligns with real-life observations, such as water sloshing in rooftop pools, and in rare cases, structural failures like the collapse of the State Audit Office building, he said.

BASED ON THE DAMAGE FROM THE RECENT EARTHQUAKE, SHOULD THE PUBLIC BE CONCERNED?