‘Aftershocks’ in Turkey after earthquake: Why do aftershocks occur?

Turkey earthquake: Reports of multiple aftershocks have emerged following the massive 7.8 magnitude earthquake early morning in Turkey. Among them is a 7.5-magnitude quake in Ekinozu, around 95 km from the epicentre of the original quake.

By: Explained Desk
New Delhi | Updated: February 7, 2023 10:43 AM IST

3 min read

Building debris and people in Diyarbakir

A man looks for survivors under the rubble following the earthquake in Diyarbakir, Turkey. (Photo: REUTERS/Sertac Kayar)

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Hours after a massive earthquake hit south-central Turkey and northern Syria, aftershocks have continued to cause damage and spread chaos. According to data from the U.S. Geological Survey (USGS), over 30 earthquakes over a magnitude of 4 have been recorded in Turkey since the original quake, with the strongest being a quake measured at 7.5 Mv at 13:24 local time (GMT +3).

Massive earthquakes are often followed by multiple aftershocks, which can last for hours or even days. These aftershocks add to the damage and chaos of the original quake, sending weakened structures crashing down and spreading fear amidst an already traumatised population.

Also in Explained | Turkey earthquake: What causes an earthquake and why can’t it be predicted?

What are aftershocks and why do they occur?

According to the USGS, aftershocks are a sequence of earthquakes that happen after a larger mainshock on a fault. Aftershocks occur near the fault zone where the mainshock rupture occurred and are part of the “readjustment process” after the main slip on the fault.

While they become less frequent with time, they can continue for days, weeks, months, or even years for a very large mainshock.

How strong are aftershocks likely to be?

Although aftershocks tend to be weaker than the main seismic event, they can cause significant damage. In Turkey, reports suggest that significant damage that has followed the original quake has been a result of aftershocks. With the main earthquake already weakening structures, aftershocks have sent many buildings tumbling.

The massive 7.5 magnitude aftershock in Turkey can actually be more devastating, say experts. This aftershock was extremely shallow, only 10 km deep, which worsens the shaking felt. The main quake was 17.9 km deep. Shallower quakes are generally felt more intense than deeper quakes due to their proximity to the surface. According to the ShakeMap, which calculates the intensity of quakes, this earthquake has been classified to have an intensity of VIII, indicating severe shaking and moderate to heavy damage. The original quake reported an intensity of IX.

Crucially, aftershocks throw a spanner in ongoing relief and rescue operations, often hurting rescuers themselves. As the death toll rises to over 1500, aftershocks will be a major challenge for authorities and international aid organisations on the ground.

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