The area of Turkey and Syria that was hit the most by Monday’s 7.8-magnitude earthquake and its aftershocks is best known for having large tremors, but it’s been decades since one last hit this big.
More than 5,000 people had died across the country.
Here’s what happened, geologically speaking, and why it caused so much damage.
Earthquakes are common in Turkey and Syria
The Arabian Peninsula is part of the tectonic plate that travels north on the Eurasian Plate, and the entire nation of Turkey is depressed.
“Arabia slowly moved north and collided with Turkey, and Turkey moved out of the way to the west,” says Michael Steckler of Columbia University’s Lamont-Doherty Earth Observatory.
That tectonic shift occurred after a millennium of earthquakes in the area, including one that hit the Syrian city of Aleppo in 1138. More recent earthquakes, such as the 1999 bombing of the city, killed many thousands.
Monday’s movement is believed to be the most powerful that Turkey has seen in more than 80 years.
This area is particularly suited to a large one
Most of the largest earthquakes in the past hundred years have been along the northern Anatolian fault.
But the stress built up over another major fault: the Eastern Anatolian fault. That fault has seen some big earthquakes in the past, Patricia Martínez-Garzón, seismologist at GFZ Potsdam, a research center in Germany, has seen. But more recently, it wasn’t so much work.
“In the last century it used to be quiet,” he said.
Some researchers have begun to suspect fault for the major tremor, according to Fatih Bulut, with the Kandilli Observatory and Earthquake Research Institute at Boğaziçi University in Istanbul. His research group and others ran computer models showing that this fault could have produced a magnitude 7.4 or larger earthquake.
“This is not surprising to us,” Bulut tells NPR.
But that doesn’t mean seismologists have been able to tell exactly when the big hit happened, according to Ian Main, a seismologist at the University of Edinburgh in the United Kingdom. The time between major fault movements can vary in fairly vague ways, he says. “They are not as a developer, not for a period of time.”
Not all the commotion falls on this one fault. The initial movement was spilled into the Dead Sea Transform, another fault region where the Arabian, Anatolian and African plates converge. And the second, a great 7.5 hour fault occurred next after the deformation but is not part of the Eastern Anatolia.
“It’s a pretty busy and complex area with multiple fault systems,” Steckler said.
This was an earthquake “applause”
This earthquake happened because “two pieces of the Earth slipped across each other,” says Steckler. This is the same type of fault that occurs on the San Andreas fault in California.
In this case, the Arabs Plat Tab Anatolica is sliding.
That slip motion also meant that the tremor extended for many kilometers along the fault, Bulut said. The area is “quite large,” he said. “Ten states in Turkey were affected by the constitution.”
Turkey has seismic codes to prevent buildings from collapsing, but Bulut says that because this region has avoided a major earthquake for a decade, it’s possible that some of the larger buildings are vulnerable. “Sometimes things are older, before the rules existed,” he says.
Steckler says he suspects even some of the newer buildings were not up to code. “I know, certainly in Istanbul, there is a lot of illegal construction going on,” he said.
More aftershocks are likely
The US Geological Survey has recorded more than 100 aftershocks in the region, and experts expect them to continue for some time.
“That whole area, all the parts of the Earth, will slowly settle and break and break, and reach a new equilibrium,” Steckler said.
#Heres #caused #earthquake #Turkey