What to know about the big quake

A major 7.8 magnitude earthquake followed by another strong quake devastated wide swaths of Turkey and Syria early Monday, killing thousands of people.

Here’s what to know:

WHAT HAPPENED?

The quake hit at depth of 11 miles (18 kilometers) and was centered in southern Turkey, near the northern border of Syria, according to the U.S. Geological Survey.

Many aftershocks rocked the two countries since the initial quake. In the first 11 hours, the region had felt 13 significant aftershocks with a magnitude of at least 5, said Alex Hatem, a USGS research geologist.

Another strong quake — magnitude 7.5 — hit Turkey nine hours after the main jolt. Though scientists were studying whether that was an aftershock, they agreed that the two quakes are related.

“More aftershocks are certainly expected, given the size of the main shock,” Hatem said. “We expect aftershocks to continue in the coming days, weeks and months.”

WHAT TYPE OF EARTHQUAKE WAS THIS?

Researchers said the earthquake was a strike-slip quake, where two tectonic plates slide past each other horizontally.

The Earth is divided up into different pieces, “kind of like a jigsaw puzzle,” said Eric Sandvol, a seismologist at the University of Missouri.

Those pieces meet at fault lines, where the plates usually grind against each other slowly. But once enough tension builds up, they can snap past each other quickly, releasing a large amount of energy.

In this case, one plate moved west while the other moved east — jerking past each other to create the quake, Hatem said.

Over time, aftershocks will start to die down and become less frequent, Sandvol said.

ARE EARTHQUAKES COMMON IN THIS AREA?

The quake occurred in a seismically active area known as the East Anatolian fault zone, which has produced damaging earthquakes in the past.

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

Turkey was struck by another major earthquake in January 2020 — a magnitude 6.7 that caused significant damage in the eastern part of the country. In 1999, a 7.4 magnitude quake struck near Istanbul and killed an estimated 18,000 people.

WHY WAS THIS EARTHQUAKE SO DEVASTATING?

The earthquake was powerful — especially for a quake that hit on land. Typically, very strong earthquakes occur underwater, Margarita Segou, a seismologist with the British Geological Survey, said.

On top of that, the quake hit near heavily populated areas. The epicenter was near Gaziantep, a major city and provincial capital in Turkey.

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

While new buildings in cities like Istanbul were designed with modern earthquake standards in mind, this area of southern Turkey has many older high-rise buildings, Jaiswal said. Rapid construction in Syria — plus years of war — may have also left structures vulnerable, researchers said.

Officials reported thousands of buildings collapsed in the wake of the earthquake. They included “pancake” collapses, where upper floors of a building fall straight down onto the lower floors — a sign that the buildings couldn’t absorb the shaking, Jaiswal said.

Rescue efforts have been hampered by freezing temperatures and traffic jams from residents trying to leave quake-stricken areas.

“This is the awful level of devastation and destruction that we would expect to see” when a strong quake hits a region with buildings that have not been shored up, said Ilan Kelman, an expert in disasters and health at University College London.