What caused the earthquake in Turkey and Syria : NPR
The area of Turkey and Syria that was hit hardest by Monday’s 7.8 magnitude earthquake and aftershocks is known for having large earthquakes, but dozens of years since this last big hit.
More than 5,00 people had died across Turkey and Syria.
Here’s a look at what happened, geologically, and why it caused so much damage.
Earthquakes are common in Turkey and Syria
The Arabian Peninsula is part of a tectonic plate that is making its way north into the Eurasian Plate, and the entire nation of Turkey is being pushed aside.
“Saudi Arabia is slowly moving north and colliding with Turkey, and Turkey is moving out of the way to the west,” says Michael Steckler of Columbia University. Lamont-Doherty Earth Observatory.
That tectonic shift has been behind earthquakes for millennia in the area, including one that flattened the Syrian city of Aleppo in 1138. More recent earthquakes, such as the one in 1999 that hit the city of İzmit, killed many thousands.
Monday’s earthquake is believed to be the strongest Turkey has seen in more than 80 years.
This particular region was due for a big one
Many of the largest earthquakes in the last hundred years have been along the North Anatolian Fault.
But stress has been building along another major fault: the East Anatolia Fault. That fault has seen some major earthquakes in the past, says Patricia Martínez-Garzón, a seismologist at the GFZ Potsdam, a research center in Germany. But more recently, there hasn’t been as much activity.
“It was unusually quiet in the last century,” she says.
Some researchers had begun to suspect that a major earthquake was to blame, according to Fatih Bulut, with the Kandilli Observatory and Earthquake Research Institute in Boğaziçi University in Istanbul. His research group and others had run computer models showing that this fault could have an earthquake of magnitude 7.4 or greater.
“This is not a surprise to us,” Bulut tells NPR.
But that doesn’t mean seismologists can tell exactly when a big one will hit, according to Ian Main, a seismologist at the University of Edinburgh in the UK. The time between large earthquakes on a fault can vary quite in unpredictable ways, he says. “It’s not like buses, they don’t come on a timetable.”
And not all the shaking happened on this one fault. The initial earthquake spread over the Dead Sea Transform, another fault region where the Arabian, Anatolian and African plates converge. And a second magnitude 7.5 earthquake struck hours later on a nearby fault that had been mapped but is not part of the East Anatolia Fault.
“It’s a pretty busy and complicated area with multiple fault systems,” says Steckler.
This was a “strike-slip” earthquake.
This earthquake occurred because “two pieces of the Earth are sliding horizontally with each other,” says Steckler. It is the same type of earthquake that occurs along the San Andreas fault in California.
In this case, the Arabian Plate is sliding off the Anatolian Plate.
That sliding motion also meant that the shaking was spread for many kilometers along the fault, says Bulut. The affected area “is quite large,” he says. “Ten cities were structurally affected in Turkey.”
Turkey has seismic codes to try to prevent buildings from collapsing, but Bulut says that because this region has escaped a major earthquake for decades, it’s possible that some older buildings are vulnerable. “Sometimes there are very old things, built before the rules existed,” he says.
Steckler says he suspects that even some newer buildings may not have been up to code. “I know, certainly in Istanbul, there is a lot of illegal construction going on,” he says.
More aftershocks are likely
The United States Geological Survey has already recorded more than a hundred aftershocks in the region, and experts expect that they will continue for some time.
“That whole area, all the pieces of the Earth are going to adjust and break and break slowly and come to a new equilibrium,” says Steckler.