The 6.3-magnitude quake that struck southern Turkey on Monday was technically an aftershock, despite its power.
The magnitude equalled that of an earthquake that struck Christchurch, New Zealand, in February 2011, killing 185 people and causing widespread destruction.
The Christchurch earthquake was later identified as an aftershock of a magnitude 7.1 earthquake in the area in September 2010. Although of a smaller magnitude than the “main shock” earthquake, the February disaster was more destructive.
The first 7.8-magnitude tremor in the disaster that killed more than 46,000 people in southern Turkey and Syria on February 6 was swiftly followed by aftershocks, one of 7.6 magnitude.
What is an aftershock and when will they end?
According to the Japan Meteorological Agency, aftershocks are caused when rock around the epicentre of an earthquake becomes unstable, after an earthquake and the tectonic plate continues to settle until no more movement can occur, at least in the near term.
The agency says violent aftershocks after large quakes typically occur within hours of the first earthquake but generally reduce in size and frequency after 10 days.
According to the United States Geological Survey “deep earthquakes (deeper than 30km) are much less likely to be followed by aftershocks than shallow earthquakes”. The February 6 earthquake had a depth of less than 18km, meaning it was classified as shallow. The USGS says that some aftershocks can happen years after the main shock.
Why are aftershocks so dangerous?
Aftershocks are highly disruptive to rescue efforts, with the potential to cause new landslides and building collapses, especially in areas where buildings are already severely damaged and unstable.
While most of the efforts to find survivors have now ended, the threat to rescuers and survivors — over one million people in Turkey are without shelter — is high during such a powerful aftershock.
Power infrastructure can also be damaged, as evidenced by video footage of Monday’s aftershock which caused lights to go out, further hampering aid and recovery efforts.
As well as causing additional death and destruction, aftershocks add to the misery and fear of survivors. One man told The National his family in northern Syria ran into the street more than a week after the initial earthquake when they were awoken in the night by the shaking of their house.