Scientists say that a rare “supershear” rupture that moved at an extremely fast speed and covered a huge area caused the Myanmar earthquake that has killed over 2,800 people. The massive Sagaing fault between the Burma and Sunda tectonic plates broke "very fast" and was spread across an area of 400km, The Independent reported.

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“The earthquake occurred on the Sagaing Fault – the major tectonic structure that accommodates the northward motion of India and western Myanmar with respect to the rest of South East Asia,” said Ian Watkinson, seismologist from Royal Holloway, University of London.

The "supershear" rupture caused a strong radiation of seismic energy to move forward at such a great speed that it could be compared to a "supersonic jet", an expert said.

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Dr Watkinson said that the fault line that runs from the Andaman Sea to the very northern part of Myanmar is similar to the San Andreas Fault in California in terms of "scale, movement and seismicity".

The magnitude 7.7 earthquake that struck on March 28 caused massive destruction and was so strong that buildings in Thailand were also hit. A high-rise building under construction in Bangkok collapsed like a pack of cards, and rescue workers searched for survivors.

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The Sagaing fault ruptured at a "velocity of about 3km per second,” seismologist Frederik Tilmann from the GFZ Helmholtz Centre for Geosciences in Potsdam, Germany, wrote on LinkedIn. 

The rupture that propagated towards the south "accelerated up to a speed of about 5 kphs," Dr Tilman said. This, he said, indicates that it was likely a “supershear” rupture.

What happens in "supershear" earthquakes?

When supershear quakes hit, the rupture underground travels at a greater speed than the seismic waves it produces. This leads to the seismic energy getting concentrated before the rupture occurs, which in turn causes greater damage through a larger area.

“The supershear rupture leads to a strong radiation of seismic energy in the forward direction,” the seismologist explained, adding that it is the "equivalent of a supersonic jet."

This fast movement of the tectonic plates worsened the situation in Myanmar and was the reason for the tremor being felt as far as 1,000 km from the epicentre in Thailand.

Seismologist Brian Baptie from the British Geological Survey (BGS) said that the massive quake ruptured a "200km section of the Sagaing Fault."