麻豆约拍

A rescue operation is underway across much of southern Turkey and northern Syria following a huge earthquake that has killed more than 2,300 people.

The 7.8 magnitude quake struck near Gaziantep in the early hours of Monday while people slept. A second 7.5-magnitude quake hit at around 13:30 local time.

How unusual is an earthquake of this magnitude - and what does a magnitude of 7.8 actually mean? Stephen Hicks, a seismologist at University College London, puts it into perspective.

(Photo: Rescue workers and volunteers conduct search and rescue operations in the rubble of a collapsed building, in Diyarbakir. Credit: Getty Images)