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Explainer | Why did the earthquake in Myanmar, Thailand cause so much damage? What science says

The earthquake with a magnitude of 7.7 near the city of Mandalay could cause fatalities between 10,000 and 100,000 people

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Rescue workers at the site of a building that collapsed in Bangkok, following Friday’s strong earthquake, on Saturday. Photo: Reuters
Reuters
A powerful earthquake of magnitude 7.7 centred in the Sagaing region near the Myanmar city of Mandalay caused extensive damage in that country and also shook neighbouring Thailand on Friday.

1. How vulnerable is Myanmar to earthquakes?

Myanmar lies on the boundary between two tectonic plates and is one of the world’s most seismically active countries, although large and destructive earthquakes have been relatively rare in the Sagaing region.

“The plate boundary between the India Plate and Eurasia Plate runs approximately north-south, cutting through the middle of the country,” Joanna Faure Walker, a professor and earthquake expert at University College London (UCL), said.

She said the plates move past each other horizontally at different speeds. While this causes “strike slip” quakes that are normally less powerful than those seen in “subduction zones” like Indonesia’s Sumatra, where one plate slides under another, they can still reach magnitudes of 7 to 8.

2. Why was Friday’s quake so damaging?

Sagaing has been hit by several quakes in recent years, with a 6.8 magnitude event causing at least 26 deaths and dozens of injuries in late 2012.

A damaged road in Naypyidaw, Myanmar, following a 7.7-magnitude earthquake on Friday. Photo: EPA-EFE
A damaged road in Naypyidaw, Myanmar, following a 7.7-magnitude earthquake on Friday. Photo: EPA-EFE
But Friday’s event was “probably the biggest” to hit Myanmar’s mainland in three quarters of a century, Bill McGuire, another earthquake expert at UCL, said.

Roger Musson, honorary research fellow at the British Geological Survey, said that the shallow depth of the quake meant the damage would be more severe. The quake’s epicentre was at a depth of just 10km (6.2 miles), according to the United States Geological Survey (USGS).

“This is very damaging because it has occurred at a shallow depth, so the shock waves are not dissipated as they go from the focus of the earthquake up to the surface. The buildings received the full force of the shaking.”

“It’s important not to be focused on epicentres because the seismic waves don’t radiate out from the epicentre – they radiate out from the whole line of the fault,” he added.

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