Explainer: Why was the Turkey-Syria earthquake so bad?

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. Photo: AP/Ghaith Alsayed

The magnitude 7.8 earthquake that struck Turkey and Syria is likely to be one of the deadliest this decade, seismologists said, with a more than 100km rupture between the Anatolian and Arabian plates.

Here is what scientists said happened beneath the Earth's surface and what to expect in the aftermath: