A shallow earthquake hit Turkey

“Ten major cities were affected by the tremors,” Tobin said. “The scale is remarkable.”

The location of the earthquakes was no surprise. They broke off near what seismologists call a “triple junction” – where the African, Arabian and Anatolian tectonic plates meet. The Eastern Anatolian Fault is a known and mapped fault system.

Eastern Anatolia, like the San Andreas Fault in California, is a strike-slip fault. The quake was the result of stress – and then landslide – as tectonic plates rubbed sideways.

Unlike other types of earthquakes, such as those produced by subduction zones, strike-slip faults are known to produce shallow earthquakes that cause shaking relatively close to the Earth’s surface.

Tobin said it was what he considers a “long” earthquake, meaning the energy traveled a great distance along the fault line.

“The length of the fault and the size of the slip is what generates the very large tremors, which cause such damage,” Tobin said.

In this case, the shaking most likely destabilized another fault line that branches off into the Eastern Anatolia fault system, triggering a magnitude 7.5 earthquake.

Affected areas in Turkey are particularly vulnerable, as many buildings were constructed with unreinforced masonry or brick and concrete that were brittle and unable to withstand strong and prolonged shaking, according to the USGS.

Tobin said early videos from Turkey showed collapsed buildings next to other buildings that appeared largely intact, a sign that those not built to modern earthquake standards were at great risk, although shaking could vary over short distances.

“This region was unfortunately at high risk for substandard structures for earthquakes, and that’s what we’re seeing playing out right now,” Tobin said.

Dozens of aftershocks have already been recorded, and they could pose a hazard for some time as the network of faults in the region absorb new stress changes in the Earth’s crust.

CORRECTION (Feb. 6, 2023, 7:01 p.m. ET): A previous version of this article misstated the name of the US agency that tracks earthquakes. It’s the US Geological Survey, not the US Geological Society.