Myanmar quake: Soil liquefaction caused severe damage, says Indian agency NCS

A rescue personnel searches for casualties at the site of a building that collapsed after a strong earthquake struck central Myanmar on Friday

India’s earthquake monitoring agency, the National Centre for Seismology (NCS), has said the earthquake that hit Myanmar and Thailand on Friday afternoon caused severe damage because its shaking matched the natural vibration of buildings.

Soil liquefaction was also a major cause of the damage, said O P Mishra, head of the NCS.Soil liquefaction happens during a strong earthquake, when the ground starts acting like a liquid instead of solid land.This usually occurs in places with loose, wet soil like sandy areas near rivers or the coast. When the earthquake shakes the ground, the water between the soil particles pushes them apart, making the soil lose its strength.

As a result, buildings, roads and other structures may sink, tilt or collapse, Mishra explained.Thailand’s capital, Bangkok, which is more than 1,000 kilometres away from the epicentre in Myanmar’s Mandalay, suffered significant damage as the rupture’s direction was towards it, he said.The NCS said seven aftershocks, ranging in magnitude from 3.5 to 7, followed the main earthquake of magnitude 7.5, which struck Mandalay around 11:50 am (IST).Northeast India also felt the main earthquake and its aftershocks.The agency said the earthquake was caused by the Sagaing Fault, a major fault line located 1,200 km east of the Indo-Burma subduction zone. The energy from the earthquake spread towards Bangkok.Another major reason for the damage was that the earthquake’s shaking frequency matched the natural vibration of buildings, making those more vulnerable, the NCS said.”The rupture direction is towards Bangkok, causing severe damage to structures in the region due to liquefactions and the matching of the earthquake-shaking frequency with the spectral frequency of the structures,” it said.

A strong aftershock of magnitude 7 occurred just 12 minutes later, about 90 km southwest of the epicentre of the first earthquake, the NCS said.It said the region has experienced major earthquakes in the past, including a magnitude-7.5 earthquake in 1912 and a magnitude-7.2 earthquake in 1956.Media reports said the earthquake killed at least three people in Bangkok and buried dozens when a high-rise building under construction collapsed.Myanmar’s military-run government has declared a state of emergency in six regions and states, including capital Nay Pyi Taw and Mandalay, the reports said.