by The earthquake in Turkey that killed more than 3,100 people and triggered a series of aftershocks ruptured on a shallow fault line just over 11 miles below the earth’s surface, making it one of the most consequential and damaging earthquakes in history recent.
Earthquakes can originate at various depths below the earth’s surface, even hundreds of kilometers deep. Effects on the surface may depend on how close the shaking is. Shallower earthquakes can be more destructive.
“Turkey is extremely earthquake-prone, but this is probably the largest earthquake in Turkey in several hundred years,” said Harold Tobin, director of the Pacific Northwest Seismic Network and professor in the Department of Earth and Space Sciences at the US. ‘University of Washington. “It is among the largest continental earthquakes.”
The magnitude 7.8 earthquake that hit the Eastern Anatolian fault zone was followed by several aftershocks, including a magnitude 7.5 earthquake recorded at an even shallower depth. That aftershock, unusually powerful for an aftershock, most likely ruptured on a nearby branching fault line within the fault system.
Turkey experienced a magnitude 7.8 earthquake in 1939. The high-power aftershock is part of what sets Monday’s quake apart.
Earthquakes stronger than magnitude 7.0 aren’t uncommon around the world — the US Geological Survey has 347 in its records since 2000, according to an NBC News analysis of its records — but focusing on magnitude alone can be misleading. Unlike this tragic event, few of the previous earthquakes have occurred on land in well-populated areas and at such shallow depths below the surface.
Magnitude can also be a confusing measure, because it uses a logarithmic scale: A magnitude 7.8 earthquake releases nearly 16 times more energy than one measured at 7.0, according to a US Geological Survey instrument.
What Turkey and neighboring Syria have experienced is one of the most damaging scenarios imaginable, highlighting the risk to earthquake-prone regions, particularly if buildings are not constructed or upgraded to modern seismic standards.
“Ten major cities were affected by the tremors,” Tobin said. “The scale is remarkable.”
The location of the earthquakes came as no surprise. They ruptured near what seismologists call a “triple junction,” where the African, Arabian, and Anatolian tectonic plates meet. The East Anatolian Fault is a known and mapped fault system.
East Anatolian, like the San Andreas Fault in California, is a strike-slip fault. The quake was the result of stress — and then slip — as tectonic plates rubbed against each other laterally.
Unlike other types of earthquakes, such as those produced by subduction zones, strike-slip faults are known to produce shallow earthquakes that cause tremors 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 are what generate the very large shaking, which causes that damage,” Tobin said.
In this case, the shaking most likely destabilized another fault line branching within the East Anatolian Fault System, resulting in a magnitude 7.5 earthquake.
Affected areas in Turkey are particularly vulnerable, because many buildings were constructed with bare masonry or brittle brick and concrete unable to withstand sustained strong shaking, 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 that weren’t built to modern seismic standards were at great risk, even though the aftershocks can vary over short periods. distances.
“This region unfortunately had a great risk of poor earthquake structures, and that’s what we’re seeing right now,” Tobin said.
Dozens of aftershocks have already been recorded, which could pose a danger for some time as the fault network in the area absorbs new stress changes in the earth’s crust.
CORRECTION (February 6, 2023, 7:01 PM ET): An earlier version of this article misreported the name of the U.S. agency that tracks earthquakes. It’s the US Geological Survey, not the US Geological Society.
This article was originally published on NBCNews.com
