Why was the Turkey-Syria earthquake so deadly?

More than 5,000 people have been killed and thousands injured by a huge earthquake which struck south-eastern Turkey, near the Syrian border on Monday morning. With a more than 100 km (62 miles) rupture between the Anatolian and Arabian plates, according to seismologists, the magnitude 7.8 earthquake is one of the deadliest this decade.

Where did it originate?

The epicenter was about 26 km east of the Turkish city of Nurdagi at a depth of about 18 km on the East Anatolian Fault. The quake radiated towards the northeast, bringing devastation to central Turkey and Syria.

During the 20th century, the East Anatolian Fault yielded little major seismic activity. “If we were going simply by (major) earthquakes that were recorded by seismometers, it would look more or less blank,” said Roger Musson, an honorary research associate at the British Geological Survey.

Only three earthquakes have registered above 6.0 on the Richter Scale since 1970 in the area, according to the U.S. Geological Survey. But in 1822, a 7.0 quake hit the region, killing an estimated 20,000 people.

Why was it so deadly?

It was a big earthquake – registered as 7.8, classified as “major” on the official magnitude scale. It broke along about 100km (62 miles) of fault line, causing serious damage to buildings near the fault.

The East Anatolian Fault is a strike-slip fault. In those, solid rock plates are pushing up against each other across a vertical fault line, building stress until one finally slips in a horizontal motion, releasing a tremendous amount of strain that can trigger an earthquake.

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.

The initial rupture for the Turkey-Syria earthquake kicked off at a relatively shallow depth.

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

Compared with the 6.2 earthquake that hit central Italy in 2016 and killed some 300 people, the Turkey-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.

Only two of the deadliest earthquakes from 2013 to 2022 were of the same magnitude as Monday’s quake.

Location map

Prof Joanna Faure Walker, head of the Institute for Risk and Disaster Reduction at University College London, said: “Of the deadliest earthquakes in any given year, only two in the last 10 years have been of equivalent magnitude, and four in the previous 10 years.”

But it is not only the power of the tremor that causes devastation.

What caused the earthquake?

The Earth’s crust is made up of separate bits, called plates, that nestle alongside each other.

These plates often try to move but are prevented by the friction of rubbing up against an adjoining one. But sometimes the pressure builds until one plate suddenly jerks across, causing the surface to move.

In this case it was the Arabian plate moving northwards and grinding against the Anatolian plate.

How are earthquakes measured?

They are measured on a scale called the Moment Magnitude Scale (Mw). This has replaced the better-known Richter scale, now considered outdated and less accurate.

The number attributed to an earthquake represents a combination of the distance the fault line has moved and the force that moved it.

A tremor of 2.5 or less usually cannot be felt but can be detected by instruments. Quakes of up to five are felt and cause minor damage. The Turkish earthquake at 7.8 is classified as major and usually causes serious damage, as it has in this instance.

Anything above 8 causes catastrophic damage and can totally destroy communities at its center.