An earthquake with a 7.7 magnitude has hit central Myanmar, the United States Geological Survey (USGS) has said, with Thailand’s capital Bangkok among other areas affected. We take a look at the origins of the event, and the scale of the disaster.
According to the USGS, a 7.7 magnitude earthquake was recorded in Mandalay, Myanmar at 6.21am GMT. The quake is thought to have been shallow, arising at a depth of just 10km (6 miles), but the damage is expected to be enormous, with multiple buildings collapsed or damaged and reports of roads left buckled and broken. The death toll is climbing, with fatalities reported not only in Myanmar but also Thailand.
Bill McGuire, emeritus professor of geophysical and climate hazards at University College London, said: “It is highly likely that build quality will generally not be high enough to survive this level of shaking, and casualty numbers will almost certainly climb significantly as more becomes known of the scale of the disaster.”
Earthquakes arise when huge slabs of rock that make up the Earth’s crust, known as tectonic plates, move against each other. According to USGS, the Myanmar quake occurred as the result of “strike slip faulting” between the India and Eurasia plates – meaning that these two tectonic plates rubbed sideways against each other.
“The quake happened on the Sagaing fault, which marks the tectonic plate boundary between the Indian plate to the west and the Eurasian plate to the east. The Indian plate is moving north along the fault compared to the Eurasian plate,” said McGuire.
The USGS says the region has experience several similar large strike slip earthquakes in the past, with six occurring within about 250km of the current earthquake since 1900 that were magnitude 7 or greater.
While many people have heard of the Richter scale to measure the size of an earthquake, the current standard is the moment magnitude scale.
“The Richter scale is an old scale developed for California. It is only good for smaller quakes, and is not very good at differentiating the sizes of bigger shocks,” said McGuire.
As the USGS website notes, the moment magnitude calculation is based on the strength of the rock where the slip occurred, the area of the fault that slipped, and the distance the fault moved.
“Thus, stronger rock material, or a larger area, or more movement in an earthquake, will all contribute to produce a larger magnitude,” it adds.
However, like the Richter scale, the moment magnitude scale is logarithmic, meaning that as the magnitude increases by one unit, the degree of ground shaking involved increases 10-fold.
“This is a major quake by any standard, and its impact is made far worse by the fact that it was very shallow – only about 10km down. If it had been 100km deep, the impact would have been much smaller, so depth as well as size is critical,” said McGuire.
But, he added, measurements do vary dependent on the locations of the seismic arrays used.
According to the China Earthquake Networks Center the Myanmar earthquake reached 7.9 magnitude, with tremors felt in China’s south-west Yunnan province.
“There has already been one large aftershock, and others can be expected in coming hours to days,” said McGuire. “These can bring down already weakened buildings and make the work of rescuers even more challenging.”
“We can’t predict earthquakes, so the answer is no,” said McGuire. “It was expected in a general sense, however, as it happened on a part of the fault that hadn’t ruptured for quite some time – known as a seismic ‘gap’.”
Dr Roger Musson, honorary research fellow at the British Geological Survey (BGS), said the last similar event in the region was in 1956.
“This means that buildings are unlikely to be designed against seismic forces, and therefore are more vulnerable when an earthquake like this occurs, resulting in more damage and higher casualties,” he said.
