What caused the earthquake in Burma – and why it caused the building to collapse in Bangkok

A major earthquake in Burma on Friday killed more than 1 people and caused the collapse of numerous buildings.

Although the Southeast Asian country is a region highly prone to earthquakes, neighboring Thailand and China – which were also affected by the quake – are not.

Thailand's capital, Bangkok, is located more than 1 kilometers away from the epicenter of Friday's earthquake - and yet an unfinished multi-story building in the city collapsed as a result of the quake.

What caused the earthquake?

The top layer of the Earth is divided into different sections, called tectonic plates, which are constantly moving. Some move alongside each other, while others are above and below each other.

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It is this movement that causes earthquakes and volcanoes.

Burma is considered to be one of the most geologically "active" areas in the world, because it is located on the cusp of the convergence of four of these tectonic plates - the Eurasian plate, the Indian plate, the Sunda plate, and the Burma microplate.

The Himalayas were formed by the collision of the Indian plate with the Eurasian plate, and the 2004 tsunami in Indonesia resulted from the movement of the Indian plate under the Burma microplate.

Rebecca Bell, professor of tectonics at Imperial College London, said that to accommodate all this movement, cracks form in the rock - which allow the tectonic plates to "slip" sideways.

Early data suggests that the movement that caused Friday's magnitude 7.7 earthquake was a "strike-slip" - where two blocks move horizontally past each other.

This matches the typical Sagaing movement.

As the plates move past each other, they can get stuck, creating friction until they suddenly loosen and the ground shifts, causing an earthquake.

Why was the earthquake felt so far away?

Earthquakes can occur up to 700km below the surface. This one was only 10km from the surface, making it very shallow. This increases the amount of shaking at the surface.

The earthquake was also very large - measuring 7.7 on the Richter scale. It produced more energy than the atomic bomb dropped on Hiroshima, according to the U.S. Geological Survey.

The strength of the earthquake was a result of the type of rupture, Bell said.

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"The nature of the straight fault means that earthquakes can erupt over large areas - and the larger the fault area, the bigger the earthquake," she explained. "There have been six earthquakes of magnitude 7 or greater in this region in the past century."

This rift also means that a lot of energy can be carried along its length - which stretches for 1200km south towards Thailand.

How earthquakes are felt on the surface is also determined by the type of soil.

In soft ground - which is what Bangkok is built on - seismic waves slow down, becoming larger in size.

So, the geology of Bangkok would have made the ground shaking more intense.

Why did only one building collapse in Bangkok?

As dramatic images emerged of tall buildings in Bangkok swaying during the earthquake - with water even gushing from rooftop pools - the unfinished Auditor General's office building was the only one to collapse.

Before 2009, Bangkok had no comprehensive safety standard for building construction to withstand earthquakes, according to Christian Málaga-Chuquitaype, professor in earthquake engineering at Imperial College London.

This means that older buildings would have been particularly at risk.

This is not unusual, as earthquake-resistant buildings can be more expensive to build and Thailand, unlike Burma, does not experience earthquakes frequently.

The building that collapsed was new, still under construction when the earthquake struck. However, investigations should be conducted to determine whether the construction was being carried out according to standards.

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However, there are other assumptions such as the quality of the material (concrete and reinforcements) and some irregularities in the structural system that "helped" the collapse.

Experts are also investigating whether the construction process of this building was "flat slab" - which is not recommended in earthquake-prone areas.