Bangkok’s soft-soil basin could amplify earthquake shaking by 3-6 times, warns Earthquake Research Centre head

Bangkok’s underlying soft-soil basin could dramatically intensify earthquake shaking and extend how long tremors last, making the capital more vulnerable than previously assumed, according to Prof Dr Pennung Warnitchai, director of Earthquake Research Centre of Thailand.

He said recent earthquakes were linked to movement along Myanmar’s Sagaing Fault, involving slip in the mid-section of the fault. However, if slip occurs in a deeper segment closer to Thailand, the impact on Bangkok could be far more severe.

The key risk: Bangkok’s geology

Pennung said the biggest danger is not distance, but Bangkok’s geological conditions. Data from vibration monitoring stations show that when seismic waves arrive outside the soft-soil basin, peak ground acceleration may be only 3-6 mg. But once those waves enter the Bangkok soft-soil basin, they can be amplified to around 20 mg—an increase of three to six times.

He added that quake waves in Bangkok have a distinctive pattern: slow shaking that lasts longer, potentially continuing for up to two minutes. These waves also tend to amplify specific frequencies—around 1.6 seconds, 2.8 seconds, and 6.3 seconds per cycle—closely matching the natural sway periods of high-rise buildings.

‘Very tall buildings’ show higher damage rates

Pennung said a phenomenon known as resonance helps explain why some buildings can suffer heavier damage than others nearby. Based on damage assessments:

• Mid-rise high-rises (around 24 storeys) with a sway period of about 2.4 seconds showed damage in around 10% of nearly 1,000 buildings surveyed.
• Very tall buildings (around 60 storeys) with a sway period of about 6 seconds were far more vulnerable: of six buildings surveyed, three were damaged—about 50% of that group.

He said damage ranged from “green” level (non-structural cracking) to “red” level (severe structural damage with deformed reinforcement), and was spread across districts with dense clusters of high-rises rather than concentrated in one single area.

Dampers and a 60-second early warning

Pennung proposed key engineering solutions, particularly the installation of dampers (vibration-reducing devices). He said most tall buildings in Thailand have low energy dissipation (damping) of only 1-2.5%, but adding dampers can raise this to 5-10%, improving performance significantly—similar to approaches used in Japan.

He also highlighted the development of an early warning system using fast-moving P-waves, which arrive before the more destructive S-waves. Measurements at the Queen Sirikit National Convention Centre suggest Bangkok could have roughly one minute of warning before strong shaking arrives.

“Those 60 seconds are enough to stop critical systems or take protective action,” he said.

Pennung said the centre aims to install structural health monitoring equipment next year in at least 20 pilot buildings in Bangkok, Chiang Mai and Chiang Rai, to improve safety and bring Thai infrastructure closer to international standards.