TEHRAN - The Sagaing Fault, passing nearby Mandalay, Myanmar, has a long history of destructive earthquakes. In 1946, in an earthquake of M7.7 similar to the 2025 earthquake, the northern part of the Sagaing Fault ruptured near Mandalay, causing widespread damage.

The 1931 earthquake of M7.5 ruptured the south Sagaing Fault near Yangon. In 1956 earthquake of M7.0 and the event of 2012 M6.9 occurred in the central and southern parts of the fault. 

The rupture of the Sagaing fault segments is divided into segments with different return periods. Paleoseismological studies show that the southern segments (near Yangon) have a return period of 100–150 years for M 7+ events, while the central Meiktila segment (which ruptured on 28-3-2025) showed a 260 km seismic gap capable of generating M 7.9 earthquakes. 

The fault slip rate of 18–49 mm/year causes stress releases, with M 7+ earthquakes typically occurring every 50–150 years, depending on the location of the fault. 

The 2025 earthquake released pent-up stress on the Meiktila section, which had not ruptured since the 1839 earthquake with an estimated magnitude of 7.9. 

The cities of Mandalay and Naypyidaw are built on soft soils prone to liquefaction and face infrastructure collapse in severe shaking. The Mw7.7 magnitude earthquake that struck Myanmar on March 28, 2025, caused significant damage in Bangkok, Thailand, approximately 1,000 kilometers from the epicenter. 

This unusual effect can be attributed to a combination of geological, structural, and seismic factors. The main earthquake that struck Myanmar and Thailand occurred on March 28, 2025, at 1:30 PM Myanmar local time. 

The earthquake near Mandalay, Myanmar's second largest city, at a depth of 10 kilometers, was followed 11 minutes later by a magnitude 6.4 aftershock and other aftershocks in the following days. 

Initial estimates suggested that about 800,000 people in Myanmar experienced a strong tremor measuring 9 on the Richter scale, while Bangkok was shaken by a moderate tremor measuring 5 to 6 on the Richter scale. However, the amplification effect in Bangkok turned the moderate tremor into a catastrophic shaking for tall and specific structures. Experts had previously warned that an earthquake of about 8 on the Saginaw fault could devastate Bangkok.

The rupture of the earthquake fault, with a rare “supershear” earthquake mechanism (where the rupture velocity was greater than the seismic wave velocity), resulted in long-lasting shaking and directed more energy towards Bangkok, 1,000 kilometers away. 

This type of movement is particularly important for tall buildings cause damage and a whiplash effect occur. This local intensification is characteristic of construction sites that have significant effects in areas with soft sediments, even at long distances in major earthquakes. 

Similar phenomena were observed in the September 19, 1985, earthquake in the Mexican city of Michoacan (330 km away).

This earthquake caused significant damage to Bangkok's tall buildings. The unfinished 33-story skyscraper in the Chatuchak 159 area suffered the most catastrophic collapse. A 33-story government office building under construction near Chatuchak Market, built by the China Railway Construction Corporation for the Audit Office of Thailand, collapsed, killing 14 people and trapping more than 378 others. 

The soft sea clay of Bangkok amplified the tremors by 3 to 4 times, affecting the building's incomplete frame. The building, being unfinished, lacked shear walls. It was a damper. Witnesses reported that its collapse occurred within two minutes of the earthquake, showing how rapid shaking can affect structures that are not poorly engineered.

The overflow of swimming pools on the roofs of several high-rise buildings caused water to flow down from the rooftops. Videos on social media showed waves of water cascading down the buildings. 

Old buildings in central Bangkok were left with cracks, broken windows, and falling debris. For example, the pool area of a luxury hotel was damaged, and the roof of a shopping mall partially collapsed. Buildings built before 2007, before Thailand’s seismic code was updated, lacked earthquake-resistant features such as reinforced concrete frames or deep foundations. 

Many of these older residential complexes and office towers suffered from cracking and partial collapse. Bangkok’s rapid urbanization has led to a proliferation of high-rise buildings on unstable ground. Older structures, including pagodas and apartment buildings, suffered minor cracks and collapses, while newer buildings that did not follow updated codes suffered significant damage. 

Buildings between 10 and 20 stories are particularly susceptible to the intensification of high-frequency seismic waves with soft soil, leading to long-term oscillations and stress in joints.

Bangkok’s subsurface is characterized by a soft marine soil layer up to 15 meters thick that amplifies long-period seismic waves. These waves coincided with shallow strike-slip earthquakes on the Sagging Fault, which occurred during the natural period of 10- to 30-story tall buildings in Bangkok, causing severe swaying and structural damage. 

This phenomenon, known as site effects, allows earthquake energy to travel efficiently over long distances, disproportionately affecting tall structures. This, in turn, amplified the city's thick marine clay, transforming moderate shaking into destructive forces for tall structures. 

On the other hand, many buildings are constructed using rigid concrete designs that are ill-suited to lateral forces, and only 10 percent of Bangkok's buildings meet current seismic standards. They are consistent with placing thousands of people at high risk in future earthquakes.

The seismic supershear rupture (faster than the shear wave velocity) and strike-slip mechanism on the Sagging Fault likely had directivity effects. The rupture to the southeast towards Thailand increased the intensity of the long-period waves reaching Bangkok. In this way, the supershear ruptures caused strong ground motion in the direction of the extension of the fault rupture front.

However, directivity effects usually decrease with distance, and at 1000 km their contribution is smaller compared to near-field areas. The main driver of damage in Bangkok appears to have been wave amplification by soft soils.

Tall buildings (10 to 30 stories) have a natural oscillation period of 1 to 5 seconds, which is consistent with the long-period seismic waves (low-frequency waves) generated by large, distant earthquakes. Over long distances (over 1000 km), the waves travel efficiently through the crust without much energy loss.

The soft clay pond of Bangkok acts like a jelly bowl and even shakes violently during earthquakes near these clay layers. Creating resonance in tall buildings, creating a "whiplash" oscillatory motion that stresses the joints, beams, and foundations of a structure. Shallow foundations built on soft clay cannot hold buildings securely during long-duration, sustained shaking.

High-rise buildings act like inverted pendulums in this environment, with their upper floors swaying violently, even if the ground motion appears slight.

Large earthquakes produce complex ground motions (such as high-frequency shaking and high-duration severe motion). The motion of tall buildings is particularly sensitive to long-period waves, which can be amplified by their natural oscillation periods.

Soft soils (common in river basins such as Mandalay) amplify the shaking and become liquefied, destabilizing the foundations of buildings. Sagging fault ruptures have caused liquefaction and worsened structural damage. 

The collapse of a Bangkok skyscraper 1000 km from the epicenter during the March 28, 2025, earthquake was attributed to the dominance of long-period waves and the amplification of site conditions.

Asymmetrical building designs or uneven mass distribution create torsional forces, increasing stress on columns and connections. 

Adjacent structures with different heights or dynamic characteristics collide with each other during shaking. In Myanmar, glass breakage and falling debris caused significant urban casualties.

Weak concrete (common in developing countries such as Myanmar) cracks under cyclic loading, leading to sudden collapse. Older buildings rarely comply with modern seismic codes. Retrofitting historic structures (e.g., Mandalay Palace) without compromising cultural heritage is complex and costly.

Clusters of tall buildings create “urban valleys” that amplify ground motion during earthquakes through wave reflection due to topographic effects. Rooftop pools, glass facades, and heavy HVAC systems add unnecessary weight and increase the stress on the structure during shaking.

Thailand historically is considered a low to moderate seismic zone, which led to insufficient seismic conservatism in the design. In Bangkok, engineers focused more on wind loads and not necessarily earthquakes.

The directivity of the Sagaing Fault rupture probably sent more energy southeastward toward Bangkok.

Bangkok’s high-rise buildings were and are uniquely vulnerable to distant earthquakes due to the intensification of long-period waves, combined with decades of unsustainable development with poor construction standards. 

Unlike shorter buildings, which are more susceptible to high-frequency, short-period shaking (which is common in major, near-earthquakes), skyscrapers are designed to be catastrophically intensified when low-frequency, long-period waves strike soft soils. An event that, even 1,000 kilometers away, with the destruction in Bangkok, added a new lesson to the lessons of earthquake engineering in the new world.

The National Disaster Management Committee declared a state of emergency in the six regions of Naypyidaw, Sagaing, Mandalay, Bago, Shan, and Magway. 

Rescue teams led by the military prioritized urban centers such as Mandalay and Naypyidaw, where infrastructure damage was severe. Hospitals in Mandalay and Naypyidaw were destroyed, and patients were treated in parking lots as emergency departments collapsed. Naypyidaw General Hospital reported 20 deaths in the first few hours after the event, and Mandalay's main hospital was short of medical supplies.