Earthquakes have occurred before, so why was there so much damage this time?
Created By RISC | 3 days ago
Last modified date : 3 days ago
Bangkok might seem largely free from earthquakes. But the city experienced 35 quakes in the 30 years from 1995 to 2025, according to the Thai Meteorological Department:
- 1995–2005: 7
- 2006–2015: 17
- 2016–2025: 13
Most of these tremors were felt in high-rise buildings and were mild to moderate. But the most recent on 28 March was the first to be noticed across the city, causing tall buildings to sway. Buildings under construction also suffered damage. The rise in frequency and intensity makes the issue of earthquakes less remote.
Why did this recent quake cause more damage? Bangkok isn’t on an active fault line or in a primary seismic risk zone. But it often experiences tremors from distant earthquakes for several geological reasons:
1. Soft Soil: Much of Bangkok (as well as many central provinces) is on ancient sediment from the Chao Phraya River. Soft clay can reach depths of 10–30 meters. This type of soil can amplify seismic waves. When earthquake waves travel from distant locations and reach these soft soil layers, the energy can become amplified at certain frequencies—making tremors more perceptible, especially in tall buildings.
2. Low-Frequency Earthquakes: Large, distant earthquakes tend to release low-frequency seismic waves, which can travel up to 1,000 kilometers without significantly losing energy. These low-frequency waves primarily affect tall buildings over 10 stories, while people at ground level might not feel much (as seen in the recent March 28 earthquake). The taller and more flexible a structure is, the more its natural frequency is likely to resonate with the earthquake waves—causing noticeable swaying.
Even though tall buildings near the Chao Phraya River face greater risks due to the amplification of seismic waves in soft soil, these risks can be mitigated with proper structural design that adheres to relevant safety standards. You can explore design guidelines for seismic safety in this article (https://mqdc.link/4lfVStr) by Sarithorn Amorncharuchit, a key developer of wellness-focused building design standards under the Research & Innovation for Sustainability Center (RISC).
Story by Napol Kieatkongmanee, Senior Sustainable Designer and TREES-A, Building Technology, Intelligent Systems, Innovative Solutions Specialist, and Ms. Sirapach Mangkang, Geographic Information System (GIS) specialist, RISC
References:
https://earthquake.tmd.go.th/document.html
https://earthquake.tmd.go.th/documents/file/seismo-doc-1606435108.pdf
https://op.mahidol.ac.th/rm/wp-content/uploads/2018/06/earthquake_140516.pdf