Separated by more than 600 miles of land, the epicenter of Friday’s earthquake in Myanmar was far from the skyscrapers of Bangkok. The collapse of a 33-storey building under construction raises questions about how the shaking in Bangkok, the capital of Thailand, compares to past earthquakes.
One of the answers lies in low-frequency seismic waves that can travel long distances and impact high-rise buildings.
During a significant earthquake event, different frequencies of shaking are emitted simultaneously. Some produce rapid vibrations, while others generate low-frequency shaking.
This was evident during the Myanmar earthquake when violent, high-frequency seismic waves caused destruction near the epicenter, taking down low-rise buildings and structures made of brittle materials.
High-frequency seismic waves released during an earthquake dissipate within the Earth, while low-frequency waves can travel further along the Earth’s crust.
Low-frequency waves were observed during the 2002 Denali earthquake in Alaska, causing vibrations as far as Texas and Louisiana.
These seismic waves resonate with tall buildings, affecting them differently based on their design and height.
Similar to tuning forks producing varied sounds, buildings react uniquely to earthquakes depending on their characteristics.
Low-frequency seismic waves played a crucial role in the 1985 earthquake that caused extensive damage in Mexico City.
Seismic waves resonated through the soft soils of the Chao Phraya River Delta in Bangkok during the recent earthquake event.
Engineers have realized the underestimated risks posed by soft soils amplifying earthquake effects in recent years.
Cities like Bangkok, Mexico City, Los Angeles, and others are subject to basin effects, increasing earthquake forces, especially at low frequencies.
In 1985, the frequency of seismic waves was critical in understanding earthquake damage in Mexico City, particularly affecting buildings between 7-18 stories tall.
Old low-rise masonry buildings performed better during earthquakes in comparison to taller structures, highlighting vulnerability despite seeming stability.
Engineers shifted to building more flexible skyscrapers in earthquake-prone regions starting from the 1950s.
Concerns persist about the vulnerability of tall buildings to less frequent but more destructive earthquakes.
The fault destruction under modern cities during a major earthquake event can have devastating effects on tall buildings, despite engineering precautions.
Dr. Heaton warns about the rapid and violent movement caused by fault slip during earthquakes, potentially leaving tall buildings unsupported.
Buildings’ bases in earthquake-prone regions must be engineered to withstand such movements to prevent catastrophic collapses.
Source: www.nytimes.com
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