Earthquake engineers explain why so many buildings collapsed in Turkey
A pair of severe earthquakes of magnitudes 7.8 and 7.5 struck southern Turkey and northern Syria on February 6, leaving over 40,000 people dead and unknown numbers injured or displaced.
Further wreaking havoc, around 25,000 buildings have either collapsed or suffered severe damage, prompting numerous questions: why did so many buildings crumble? Was it simply the enormous magnitude and violence of the quake? Or was the problem the design and construction of the buildings?
To learn more, Interesting Engineering (IE) spoke with two experts whose research focuses on the area of geotechnical earthquake engineering.
What caused so many buildings to collapse in Turkey?
"As seismic waves from an earthquake approach a site where a building is located, they may encounter softer geologic materials (soils) near the ground surface," explained James Kaklamanos, Associate Professor of Civil Engineering at Merrimack College in Massachusetts, U.S.
"The properties of these soft materials often cause the waves to experience large amplifications as they approach the ground surface, similar to shaking a bowl of Jello," he added.
In an earthquake-resistant design, Kaklamanos emphasized that these site-specific (geological) effects must be taken into consideration. Buildings may fail catastrophically if they cannot appropriately bear earthquake loads from the ground, as we have tragically witnessed in Turkey and Syria.
"The quality of design and construction largely influence how buildings perform in earthquakes, but site-specific geologic conditions can have a profound influence on the loading that each building experiences," he said.
"Buildings that fail during earthquakes are often made of materials that are too brittle, such as concrete and masonry, without adequate reinforcement," Kaklamanos explained.
He highlighted that reinforcing steel (or "rebar") provides additional flexibility to buildings made of these materials. This approach offers structures a greater ability to handle large deformations during earthquakes without failing.
"Many of the buildings that collapsed in Turkey and Syria appear to be constructed of reinforced concrete, but the amount of reinforcing steel was likely insufficient to handle the loads from the earthquake," he said.
"Such failures are often a combination of providing inadequate structural capacity while underestimating the potential seismic hazards (earthquake ground motions) at a site," he concluded.
Why were buildings not able to resist significant earthquake forces?
IE spoke with Anastasios Sextos, a professor of earthquake engineering at the University of Bristol in the U.K. He's also head of the Earthquake and Geotechnical Engineering Research Group there, which focuses on ways to improve infrastructure resilience to extreme events.
He stated that the considerable structural damage is a result of both the fragility of the structures and the earthquake intensity. Sextos clarified that in some locations, the earthquake intensity was significantly higher than levels incorporated in structural design.
"Unfortunately, even though the Turkish seismic code is advanced and up to date, buildings constructed before 2000 as well as newer ones – for which the design regulations have not been duly implemented – were not able to resist the significant earthquake forces," Sextos explained.
"[Subsequently, they] collapsed in a brittle manner," he added.
"It is important to remember that the current state of practice worldwide ensures that the buildings will be able to resist strong earthquakes by means of controlled damage and energy absorption," he said.
Sextos stressed to IE that it is, therefore, of paramount importance to strengthen substandard buildings as well as enforce code compliance to the new ones to prevent further pain and loss of life in case of the next strong earthquake.