Turkey, Syria jolted by over 70 aftershocks after 7.8-earthquake: What are they and how destructive can they be?

Over 4,300 people dead, thousands of buildings destroyed, lives upended and sheer panic and terror. That’s the powerful 7.8-magnitude earthquake that jolted Turkey and Syria on Monday morning, even as people slept comfortably in their homes.

But even as rescuers race against the clock to rescue people trapped in the rubble, worry is etched on the faces of people in the region, as they fear strong aftershocks to rock the area again. On Monday, nine hours after the initial quake flattened the region, a strong aftershock measuring 7.5 on the Richter scale struck the area, adding more destruction — shaking buildings and infrastructure that have been badly weakened by the initial quake. At the time of this report being published, another aftershock measuring 5.6 on the Richter scale struck central Turkey, reported Reuters.

According to the US Geological Survey, there have been at least 77 aftershocks, including a major one at 7.5 magnitude. Three of the aftershocks have measured 6.0 or greater, said the USGS, adding that the aftershocks stretched for more than 300 kilometres along the fault zone that ruptured in southern Turkey, oriented from southwest to northeast and stretching from the border with Syria up through the province of Malatya.

Animated map of seismicity near Turkey quakes starting ~3am local time plotting Feb 6 M7.8 mainshock (pink), early aftershocks (orange), M7.5 aftershock to the north (tan), and subsequent aftershocks in the north (tan). Time vs. magnitude progression shown on bottom graph. pic.twitter.com/TTa7qdZWzO

— USGS Earthquakes (@USGS_Quakes) February 7, 2023

But what exactly are aftershocks? How strong can they be? How long will they continue?

What are aftershocks?

Aftershocks are basically smaller earthquakes that take place in the same general area after the larger or “mainshock”. The USGS notes that aftershocks normally occur within one-two fault lengths away and are part of the “readjustment process” after the main slip on the fault.

The frequency of these aftershocks decreases with time; though they can continue for days or even weeks after the mainshock.

The USGS adds that historically, deep earthquakes (greater than 30 km) are much less likely to be followed by aftershocks than shallow earthquakes.

Also read: Can earthquakes be predicted? What Dutch researcher said about Turkey, Syria on 3 February

The Britannica Encyclopaedia explains that although the shaking intensity associated with most aftershocks is relatively small compared with that of the principal earthquake, it can be large enough to hamper rescue efforts by further destabilising buildings and other structures. In addition, aftershocks can be stressful for local residents coping with the damage and loss of life wrought by the principal quake.

And the case was no different with the Turkey-Syria earthquake. In the first 12 hours after the quake struck, there were as many as 39 aftershocks, which shook Turkey and neighbouring countries of Syria, Lebanon, and Cyprus.

How strong can aftershocks be?

In general, aftershocks tend to be weaker than the main seismic event, but that doesn’t mean they don’t cause significant damage. In Turkey, some of the aftershocks were over 6.0 in magnitude, causing even more panic among the residents.

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 New York Times reported that based on statistical analyses of quakes worldwide, the most powerful aftershock on Monday should have been around 6.8, or only about one-thirtieth as powerful as the first quake. However, the strongest aftershock was recorded at 7.5.

“There’s nothing magic about aftershock magnitude,” Susan Hough, a seismologist with the United States Geological Survey to the New York Times, adding, sometimes an aftershock is even larger than the initial quake.

Also read: From Turkey to Nepal, the deadliest earthquakes that rocked the world

Residents spoke of their horror as they felt the major aftershock. Tulin Akkaya, who resides in the southeastern city of Diyarbakir, told AFP, “I am so scared. I felt (the aftershock) so strongly because I live on the top floor. We rushed outside in panic. It was almost the same as the morning’s earthquake. I can’t go back to my apartment now, I don’t know what will happen next.”

Kahramanmaras-based reporter Melisa Salman was also quoted as telling AFP, “That was the first time we have ever experienced anything like that. We thought it was the apocalypse.”

How long will they continue to rattle the area?

Seismologists note that aftershocks can continue for hours and even days after the main event, which, in most cases, hamper search and rescue operations.

In the case of the Turkey-Syria quake, the aftershocks are devastating in their own right, causing buildings to collapse and knocking down an ancient Roman castle. And experts believe that this could continue for months.

“The number of aftershocks will decrease with time, but large events can continue to occur, for months or longer,” Jascha Polet, a geophysics researcher at Cal Poly Pomona, tweeted Monday morning.

Chris Elders, professor at the School of Earth and Planetary Sciences at Curtin University in Perth Australia agreed with this point of view and told Al Jazeera, “People will continue to feel the effects of the earthquake for some time in this area.”

What’s the ground situation?

Rescuers and volunteers are battling nightfall and the extreme cold temperatures to continue their operations. According to a CNN report, the death toll now stands at 4,372 deaths — 2,921 in Turkey and 1,451 in neighbouring Syria.

And the quake has also prompted assistance and aid from across the world — with President Joe Biden “reaffirming” that the United States is ready to help Turkey in the aftermath of a recent earthquake and “expressed condolences on behalf of the American people”.

India, too, has extended aid, with the first consignment of earthquake relief departing from Hindon Airbase in Ghaziabad for Turkey.

With inputs from agencies

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