“Ten major cities were affected by tremors,” Tobin said. “The scale is remarkable.”
The location of the earthquakes was not a surprise. They broke near what seismologists call a “triple junction,” where the African, Arabian, and Anatolian tectonic plates meet. The East Anatolian Fault is a known mapped fault system.
Eastern Anatolia, like the San Andreas fault in California, is a course failure. The earthquake was the result of stress, and then slippage, when the tectonic plates rubbed laterally against each other.
Unlike other types of earthquakes, such as those produced by subduction zones, strike faults are known to produce shallow earthquakes that trigger tremors relatively close to the Earth’s surface.
Tobin said it was what he considers a “long” quake, meaning the energy traveled a long distance along the fault line.
“The length of the fault and the size of the slip is what generates the large jolt that causes such damage,” Tobin said.
In this case, the tremor most likely destabilized another branching fault line within the East Anatolian fault system, causing a magnitude 7.5 earthquake.
The affected areas in Turkey are especially vulnerable, because many buildings were built with unreinforced masonry or brick and concrete that is brittle and unable to withstand strong and prolonged shocks. according to the USGS.
Tobin said early videos from Turkey showed collapsed buildings alongside other buildings that appeared to be largely intact, a sign that those not built to modern seismic standards were at great risk, although tremors can vary over short distances. .
“Unfortunately, this region was at great risk of substandard structures for earthquakes, and that’s what we’re seeing right now,” Tobin said.
Dozens of aftershocks have already been recorded, and they could be a danger for some time as the fault network in the area absorbs new changes in stress in the Earth’s crust.
CORRECTION (February 6, 2023, 7:01 PM ET): An earlier version of this article misrepresented the name of the US agency that tracks earthquakes. It is the United States Geological Survey, not the United States Geological Society.