BANGKOK— For decades, residents of Bangkok have viewed earthquakes as a distant problem, something that happens in the rugged mountains of the north or across the border in Myanmar. However, new research from one of Thailand’s leading seismic experts suggests that the very ground the capital is built on may be its greatest hidden threat.
Prof. Dr. Pennung Warnitchai, Director of the Earthquake Research Centre of Thailand, has issued a sobering warning : Bangkok sits atop a “soft-soil basin” that acts like a massive amplifier for seismic waves. According to his latest data, this geological “bowl” can intensify the shaking from distant earthquakes by 3 to 6 timescompared to firmer ground outside the city.
The “Jelly Bowl” Effect: Why Bangkok is Unique
Bangkok is famously built on the low-lying floodplain of the Chao Phraya River. While this fertile soil helped the city grow into a megacity, it poses a significant engineering challenge during a tremor.
The city sits on a thick layer of soft clay, often referred to as “Bangkok Clay,” which reaches depths of 15 to 30 meters, followed by alternating layers of sand and stiff clay. This entire basin extends down several hundred meters before hitting solid bedrock.
“The biggest danger to Bangkok is not the distance from an earthquake’s epicenter, but our unique geological conditions,” Dr. Pennung explained. When seismic waves travel through the earth and hit this soft basin, they slow down and grow in size, much like waves in the ocean growing taller as they reach the shore.
Shocking Data from Vibration Monitoring
To understand the scale of the risk, the Earthquake Research Centre analyzed data from monitoring stations across the region. The findings revealed a dramatic contrast:
- Outside the Basin:Seismic waves might register a peak ground acceleration of only 3 to 6 mg (a measure of shaking intensity).
- Inside Bangkok:Those same waves, once they enter the soft-soil basin, can be amplified to roughly 20 mg.
This 300% to 600% increase in intensity is accompanied by another dangerous factor: duration. While a typical earthquake might feel like a quick jolt on firm ground, the soft soil in Bangkok causes the ground to sway for much longer—sometimes up to two full minutes.
High-Rise Buildings: The Resilience Gap
The most concerning part of Dr. Pennung’s research involves the city’s skyline. As the ground sways, it creates a “resonance” effect with tall buildings. If the frequency of the earthquake matches the natural “swing” of a building, the damage can be catastrophic.
A recent survey conducted by the National Earthquake Research Center (EARTH) following tremors in 2025 provided a clear look at which structures are most at risk:
- Mid-rise buildings (around 24 storeys):About 10% of the 1,000 buildings surveyed showed signs of damage, mostly non-structural cracks.
- Very tall buildings (60 storeys or more):These were far more vulnerable. Out of a small sample of six buildings surveyed, 50% (three buildings)suffered damage.
“We are seeing a pattern where very tall buildings have sway periods that closely match the amplified frequencies of the Bangkok basin,” said Dr. Pennung. “This makes them much more susceptible to heavy swaying and structural stress.”
Three Fault Lines to Watch
While Bangkok does not sit directly on a major fault line, Dr. Pennung identified three primary sources of seismic energy that could trigger the “amplifier” effect:
- The Sagaing Fault (Myanmar):A highly active fault capable of producing Magnitude 8.0 earthquakes.
- The Three Pagodas and Si Sawat Faults (Western Thailand):Located closer to the capital, these could cause severe shaking if a major slip occurs.
- The Andaman Subduction Zone:An underwater zone that could produce massive earthquakes of Magnitude 8.5 or higher. Researchers note there hasn’t been a major release of energy here in over 260 years.
Solutions: The 60-Second Lifeline
The news isn’t all grim. Dr. Pennung and his team are pushing for two major upgrades to Thailand’s infrastructure to save lives and property.
1. Structural Dampers
Most tall buildings in Thailand currently have low “damping” rates (the ability to absorb and stop vibration), usually around 1% to 2.5%. By installing industrial dampers—essentially giant shock absorbers—buildings can increase their damping to 5% or 10%. This is the gold standard used in earthquake-prone countries like Japan.
2. Early Warning Systems
The Earthquake Research Centre is developing a system that detects “P-waves” (fast-moving, less destructive waves) before the damaging “S-waves” arrive.
- The Goal:Provide a 60-second warningto the city.
- The Impact:One minute is enough time to automatically shut down gas lines, stop elevators at the nearest floor, and allow people to move away from glass windows.
A Call for Modern Standards
As Bangkok continues to grow vertically, the research from Dr. Pennung serves as a critical wake-up call for urban planners and developers. The “soft-soil” factor is no longer a theoretical risk; it is a measurable reality.
“ Earthquakes are an unavoidable risk, but they can be managed through knowledge and technology,” Dr. Pennung concluded. “Our goal is not to cause panic, but to ensure that the buildings of the future are designed for the ground they actually stand on.”
