Türkiye and Syria earthquake: what happened beneath the surface?

Sismologists say the magnitude 7.7 earthquake that struck Türkiye and Syria is likely to be one of the deadliest this decade.

At the time of writing, the death toll in Türkiye had climbed to more than 5,400, while more than 1,700 people have been killed in Syria, according to officials.

With its epicentre 26 km east of the Turkish city of Nurdagi, had a depth of about 18 km on the East Anatolian Fault, running from eastern to south-central Türkiye.

It radiated towards the northeast, with a more than 100 km rupture between the Anatolian and Arabian plates.

Earthquakes can be induced by a wide range of causes, including man-made such as mining and other extractive activities. While the damage caused by these activities can be minimised, natural earthquakes caused by sudden shifts in the earth’s tectonic plates, cannot be prevented.

What is the East Anatolian Fault?

The East Anatolian Fault, which was responsible for Monday’s disaster, is a strike-slip fault - a type where two tectonic plates slide past each other horizontally.

The Earth is divided up into different pieces, “kind of like a jigsaw puzzle,” said Eric Sandvol, a seismologist at the University of Missouri.

Those pieces meet at fault lines, where the plates usually grind against each other slowly. But once enough tension builds up, they can snap past each other quickly, releasing a large amount of energy.

In this case, one plate moved west while the other moved east - jerking past each other to create the quake.

During the 20th century, the East Anatolian Fault yielded little major seismic activity.

The San Andreas Fault in California is perhaps the world's most famous strike-slip fault, with scientists warning that a catastrophic quake is long overdue.

How strong was this earthquake?

On average, there are fewer than 20 quakes over 7.0 magnitude in any year, making Monday's event severe.

According to the US Geological Survey, only three earthquakes have registered above 6.0 on the Richter Scale since 1970. But in 1822, a 7.0 quake hit the region, killing an estimated 20,000 people.

Compared with the 6.2 earthquake that hit central Italy in 2016 and killed some 300 people, the Türkiye-Syria earthquake released 250 times as much energy, according to Joanna Faure Walker, head of the University College London Institute for Risk and Disaster Reduction.

Shallow depth

The initial rupture for the Türkiye-Syria earthquake kicked off at a relatively shallow depth. "The shaking at the ground surface will have been more severe than for a deeper earthquake of the same magnitude at source," David Rothery, a planetary geoscientist at the Open University in Britain, said.

The earthquake was powerful - especially for a quake that hit on land. Typically, very strong earthquakes occur underwater, Margarita Segou, a seismologist with the British Geological Survey, said.

How long will aftershocks last?

Eleven minutes after the initial quake, the region was hit by a 6.7-magnitude aftershock. A 7.5-magnitude quake came hours later, followed by another 6.0 shock in the afternoon.

Scientists expect these aftershocks to continue for a while as seismic activity is now spreading to neighbouring faults.

After the deadly 1822 event, aftershocks carried on into the following year.

Seismically active region

“Almost all of Türkiye is really seismically active,” Sandvol said. “This is not something new to the country.”

Türkiye was struck by another major earthquake in January 2020 - a magnitude 6.7 that caused significant damage in the eastern part of the country. In 1999, a 7.4 magnitude quake struck near Istanbul and killed an estimated 18,000 people.

Why the final death toll could rise 

Earthquakes of equal magnitudes in similarly populated areas have killed thousands of people. Nepal's 7.8-magnitude earthquake in 2015 claimed nearly 9,000 lives.

"It's not going to be good," said Roger Musson, an honorary research associate at the British Geological Survey. "It will be in the thousands, and could be in the tens of thousands."

Cold winter weather, he added, means that people trapped under rubble have less chance at survival.