AP EXPLAIN: What you need to know about the earthquake in Turkey

A 7.8 magnitude earthquake followed by another strong quake devastated large parts of Turkey and Syria on Monday, killing thousands of people.

This is what you need to know:

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WHAT HAPPENED?

The quake struck at a depth of 18 kilometers (11 miles) and was centered in southern Turkey, near the northern border with Syria, according to the United States Geological Survey (USGS).

Several aftershocks have shaken the two countries since the first quake. In the first 11 hours, the region had recorded 13 significant aftershocks of at least magnitude 5, said Alex Hatem, a USGS research geologist.

Another strong earthquake, measuring 7.5 magnitude, struck Turkey nine hours after the first shock. Although scientists were studying whether it was an aftershock, they agreed that the two quakes are related.

“More aftershocks are certainly expected, given the magnitude of the mainshock,” Hatem said. “We anticipate that the aftershocks will continue in the coming days, weeks and months.”

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WHAT KIND OF EARTHQUAKE WAS IT?

According to the researchers, it was a slip earthquake, in which two tectonic plates slide horizontally in opposite directions.

The Earth is divided into different pieces, “sort of like a puzzle,” explains Eric Sandvol, a seismologist at the University of Missouri.

Those pieces meet each other at fault lines, where the plates often slowly rub against each other. But once enough tension builds up, they can quickly move in opposite directions, releasing a huge amount of energy.

In this case, one plate moved west while the other moved east, shaking each other strongly to create the quake, Hatem said.

Over time, the aftershocks will start to diminish and become less frequent, Sandvol said.

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ARE EARTHQUAKES FREQUENT IN THIS AREA?

The earthquake occurred in a seismically active zone called the East Anatolian fault, which has produced damaging earthquakes in the past.

“Almost all of Turkey is really seismically active,” Sandvol said. “This is not something new in the country.”

Turkey was hit by another strong earthquake in January 2020, with a magnitude of 6.7, which caused significant damage in the east of the country. In 1999, a magnitude 7.4 earthquake struck near Istanbul, killing some 18,000 people.

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WHY WAS THIS EARTHQUAKE SO DEVASTATING?

The earthquake was very strong, especially for a tremor that shook the mainland. Margarita Segou, a seismologist with the British Geological Survey, explained that very strong earthquakes usually occur underwater.

In addition, the earthquake occurred near densely populated areas. The epicenter was located near Gaziantep, a large city and the capital of a Turkish province.

The affected regions are also home to vulnerable buildings, said Kishor Jaiswal, a USGS civil engineer.

While new buildings in cities like Istanbul were designed with modern anti-seismic standards in mind, there are many old skyscrapers in this area of ​​southern Turkey, Jaiswal explained. Rapid construction in Syria, coupled with years of warfare, could also have left the structures vulnerable, the researchers added.

Authorities reported that thousands of buildings collapsed from the quake. Among them were “pancake” collapses, in which the upper stories of a building fall directly on the lower ones, a sign that the buildings were unable to absorb the shock, Jaiswal said.

Rescue efforts have been affected by low temperatures and traffic jams, the latter caused by residents trying to leave quake-hit areas.

“This is the appalling level of devastation and destruction we would expect to see” when a strong quake hits a region with unreinforced buildings, said Ilan Kelman, a disaster and health expert at University College London.

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Associated Press writers Jill Lawless and Cassandra Allwood contributed to this report.

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The Associated Press Department of Health and Science receives support from the Howard Hughes Medical Institute Science and Educational Media Group. The AP is solely responsible for all content.