“Ten major cities were hit by quakes,” Tobin said. “The scale is remarkable.”
The location of the earthquakes was no 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 well-known, mapped fault system.
The East Anatolian is, like the San Andreas Fault in California a strike-slip error. The quake was the result of stress — and then a slip — as tectonic plates rubbed sideways against each other.
Unlike other types of earthquakes, such as those produced by subduction zones, strike-slip faults are known to produce shallow earthquakes that shake relatively close to the Earth’s surface.
Tobin said it was what he considers a “long” quake, meaning energy traveled a great distance along the fault line.
“The length of the fault and the size of the slip cause the very large shaking that causes such damage,” Tobin said.
In this case, the shaking most likely destabilized another fault line that branched within the East Anatolian fault system and produced a magnitude 7.5 earthquake.
The affected areas in Turkey are particularly vulnerable, as many buildings are built with unreinforced masonry or brick and concrete, which are brittle and cannot withstand strong and prolonged vibrations. according to the USGS.
Tobin said early videos from Turkey showed collapsed buildings next to others that appeared largely intact, a sign that those not built to modern seismic standards were at high risk, although tremors can vary over short distances.
“This region unfortunately had a high risk of substandard structures for earthquakes, and that’s what we’re seeing playing out now,” Tobin said.
Dozens of aftershocks have already been recorded, which could pose a threat for some time as the area’s network of faults absorb new changes in the 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 U.S. earthquake tracking agency. It’s the US Geological Survey, not the US Geological Society.
