What caused the Turkey and Syria earthquake?

Around the world, most big earthquakes happen along tectonic plate boundaries. Tectonic plates move apart from each other at divergent plate boundaries. They come together at convergent boundaries. And they slide past one another, side-by-side, at transform plate boundaries. Transform boundaries are characterized by something called strike-slip faulting, which is faulting that occurs where the two blocks are moving horizontally past each other.

The transform boundary that most people know in the U.S. is the San Andreas Fault, which is a big strike-slip fault in California. In eastern Turkey, a strike-slip fault forms part of a complicated plate boundary where three small plates interact. The 7.8 earthquake occurred along one of these plate boundaries called the East Anatolian Fault. The fault extends on a diagonal line from the Mediterranean Sea roughly 450 miles northeast to the Turkish town of Karlıova. It is a transform plate boundary, and it separates the Arabian Peninsula from Turkey.

In a motion called left-lateral slip, the fault’s west side moved southwest and the east side moved northeast. In photos of roads after the earthquake, you can see evidence of the motion. If you’re driving on a road and come up to the fault trace, you’ll see a break. To continue on the road, you have to move to the left because the road has been displaced by left-lateral slip.