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Myanmar Earthquake: Earthquakes of magnitude 7.7 and at least three aftershocks struck Myanmar on Friday (March 28), according to the United States Geological Survey (USGS), topping buildings in the country’s second-largest city, Mandalay, and bringing down a skyscraper under construction in Bangkok, Thailand. At least one person was killed and dozens of workers rescued from under the rubble of the skyscraper, according to a report by Reuters.
Notably, the quake of magnitude 7.7 was the strongest one anywhere in the world in the last two years, USGS data show.
The epicentre of the earthquake was about 17.2 km from Mandalay, which has a population of around 1.5 million people. It was a shallow earthquake at a depth of just 10 km, according to USGS.
Here is a look at what causes earthquakes, why shallow earthquakes are a concern, and how frequent they are in Myanmar.
An earthquake is an intense shaking of the ground caused by movement under the earth’s surface. It happens when two blocks of the earth suddenly slip past one another. This releases stored-up ‘elastic strain’ energy in the form of seismic waves, which spread through the earth and cause the shaking of the ground.
The earth’s outermost surface, crust, is fragmented into tectonic plates. The edges of the plates are called plate boundaries, which are made up of faults. The tectonic plates constantly move at a slow pace, sliding past one another and bumping into each other. As the edges of the plates are quite rough, they get stuck with one another while the rest of the plate keeps moving. Earthquake occurs when the plate has moved far enough and the edges unstick on one of the faults.
USGS says that “the location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicentre.”
Shallow quakes are generally more dangerous as they carry more energy when they emerge to the surface when compared to quakes that occur deeper underneath the surface. While deeper quakes do indeed spread farther as seismic waves move radially upwards to the surface, they lose energy while travelling greater distances.
Apart from the depth, the magnitude of an earthquake is also an indicator of how destructive a quake could be. Magnitude tells how big the seismic waves are, while strength refers to the energy they carry. “While each whole number increase in magnitude represents a tenfold increase in the measured amplitude, it represents 32 times more energy release,” the USGS said.
Put simply, the seismic waves produced by a magnitude 6 earthquake have 10 times higher amplitude than the ones produced by a magnitude 5 earthquake. The energy differential is even higher, 32 times for every change of 1 in magnitude.
Earthquakes are relatively common in Myanmar due to the Sagaing Fault, which runs north to south through the centre of Myanmar and has a history of significant seismic activity. Between 1930 and 1956, the country witnessed six strong quakes of 7.0 magnitude or higher near this fault line. The epicentre of Friday’s quake, located near Mandalay, is also located on this fault.
Moreover, earthquakes of magnitude 7 or above are not uncommon across the world. There usually are about a dozen such events every year. But there have been just three in the last two years
