DNA Explainer: What are aftershocks and what causes them?

Turkey and Syria were rocked by three consecutive hits of massive earthquakes, killing over 5000 people and destroying buildings, and infrastructure. As per the US Geological Survey's data, Turkey has been hit by over 30 earthquakes of 4 magnitudes since the original quake. Massive earthquakes are often followed by aftershocks that can last for hours and even days. What are aftershocks and what causes them?

What is aftershock?

Aftershock is a smaller earthquake that occurs after the main quake in the same area. This happens because the displaced crust adjusts itself to the effects of the main shock.  Large earthquakes can have thousands of instrumentally detectable aftershocks. The magnitude and frequency of these aftershocks keep decreasing according to a consistent pattern. 

The aftershocks mostly occur over the full area of the fault rupture (The plane, or surface formed between the two rock blocks that slip one with the other during an earthquake). Or it occurs along the fault plane or along other faults that fall on the same strain as the affected area. Typically, aftershocks are found up to a distance equal to the rupture length away from the fault plane.

Read: Turkey-Syria Earthquake live updates: Death toll exceeds 5,000 mark, second IAF C17 with aid departs from Hindon Airbase

Even though the aftershocks are weaker than the main quake still they can cause severe damage. In Turkey too, significant damage was caused by the aftershocks that occurred after the main jolt. With the main earthquake already weakening structures, aftershocks have sent many buildings tumbling.

Turkey was hit by a massive earthquake of 7.8 magnitudes in the early morning of February 6, followed by a quake of 7.5 magnitudes in the afternoon and a 6-magnitude quake in the evening.