Author: Rebecca Owen

Next steps in seismic hazard reduction after the Turkey earthquakes

Source(s): Temblor
Yellow building collapsed after an earthquake.
4.murat/Shutterstock

In February 2023, Turkey and Syria experienced two powerful earthquakes — the first, a magnitude-7.8 and second, a magnitude-7.5 event — just nine hours apart. More than 50,000 people were killed and cities were leveled.

As the region reels from the devastation, researchers are grappling with questions about protecting vulnerable areas and infrastructure to prevent future deaths in this seismically active location. A recent commentary in Nature Communications Earth and Environment revisited the effects of these quakes in both Turkey and Syria, and outlined the need to reassess hazards and risk in this region to protect people from future tragedy.

A pair of unusual earthquakes

At 4:17 a.m. on Feb. 6, 2023, most people in southeastern Turkey were asleep when the shaking began, causing buildings to collapse throughout the densely populated area. Nine hours later, the second quake amplified the unfolding humanitarian crisis. Buildings that were damaged in the first quake fell or were rendered more unstable. As a result, millions of people in Turkey and Syria have been displaced. This pair of earthquakes ranks as the fifth deadliest in the 21st century.

This region is well-known for its seismicity, having experienced several large earthquakes in the past. The East Anatolian Fault Zone forms the boundary between the Anatolian Plate and the northern tip of the Arabian Plate. A location like this one boasts abundant natural resources, like water and fertile growing regions. But, it also has active fault zones and plate movements that can disrupt population centers and industry if an earthquake occurs. This confluence of cities and seismic activity makes it all the more necessary to understand the potential hazards and to work quickly to prevent future damage and loss when large earthquakes occur.

The East Anatolian Fault in Türkiye

Historically, earthquakes along the East Anatolian Fault Zone have varied in magnitude, from moderate (magnitude 6 or greater) to large (greater than magnitude 7), and these past earthquakes ruptured separate parts of the fault. The February 2023 earthquake pair was different. Together, these earthquakes ruptured several segments of the East Anatolian Fault Zone, “leading to a larger slip than the deficit accumulated since the last large events,” says Luca Dal Zilio, co-author of the recent article and a senior researcher at ETH Zurich. “This unusual behavior contributed to the unexpected magnitude and damage.”

Dangerous buildings

In Syria, where the population is already extremely vulnerable due to ongoing war, structures may be built with substandard materials and design not suitable to withstand a large earthquake. But even in Turkey, more than 150,000 buildings collapsed or were damaged beyond repair. Originating in 1947 and last updated in 2018, Turkey’s building codes address seismic concerns in the region, but these building specifications need to be followed and enforced in order to build earthquake resilience, writes Dal Zilio in the study.

One type of structure that was prone to collapse in Turkey was nonductile reinforced concrete buildings. These older buildings lack steel reinforcements that can keep them upright and prevent “pancaking” — where one story collapses onto the one below it. A second type of susceptible building was a “soft-story” building, says Osman Ozbulut, an associate professor of civil engineering at the University of Virginia who was not involved with the study. This type of building features a garage or open commercial space on the first level that has less support than the building’s upper levels. Both older and newer soft-story buildings exhibited this sort of collapse.

“Buildings that were not up to date or designed and constructed with poor quality materials did not have a chance to survive this earthquake,” says Ozbulut. “However, there are also many buildings — probably designed based on modern code requirements — that did not collapse but had heavy-to-moderate damage. Most of these buildings will now be demolished,” he says.

Modern seismic building codes are intended to anticipate the damage done to buildings while still protecting their inhabitants after a strong earthquake. “This performance objective is called ‘life safety,” says Ozbulut. A building designed with life safety as its functional goal will sustain damage in a controlled manner and stay standing after an earthquake.

Sketching illustrating how three different types of buildings behave in the event of an earthquake.
Resilient and Ad-vanced Infrastructure Laboratory (RAIL) at the University of Virginia, led by Ozbulut Osman
This sketch illustrates how three different types of buildings behave in the event of an earthquake. The first, a conventional multi-story building, will sway laterally, which can cause both structural and non-structural damage. The second type shows a building with seismic dampers, in which the swaying is dramatically reduced. The third type is a seismically isolated building. All movement is concentrated at the base, in the seismic isolator.
This sketch illustrates how three different types of buildings behave in the event of an earthquake. The first, a conventional multi-story building, will sway laterally, which can cause both structural and non-structural damage. The second type shows a building with seismic dampers, in which the swaying is dramatically reduced. The third type is a seismically isolated building. All movement is concentrated at the base, in the seismic isolator. Credit: Resilient and Ad-vanced Infrastructure Laboratory (RAIL) at the University of Virginia, led by Ozbulut Osman

New Zealand’s Christchurch earthquakes in 2010 and 2011 revealed the limits of building codes based on life safety requirements. Thousands of buildings designed with this modern code were damaged so extensively during the quakes that they had to be demolished, says Ozbulut.

After Christchurch, the engineering community was alarmed at the performance failures of modern buildings during these strong earthquakes. One design initiative to come from the destruction and loss in New Zealand was to build structures with functional recovery in mind. Functional recovery is when buildings are designed and constructed not only to protect inhabitants, but also to prevent damage and enable reoccupancy within an acceptable period of time after an earthquake, explains Ozbulut. Although different design strategies can be employed to achieve a higher performance objective, seismic protection technologies such as base isolation systems and seismic dampers can facilitate ‘functional recovery’ after a strong earthquake, he says.

Risk throughout the region

“The Turkey earthquake sequence is a serious alarm for developers to re-think about the acceptable risks during an earthquake,” says Ozbulut. Other seismically active areas nearby, like the segment of the North Anatolian Fault system south of Istanbul that runs beneath the Marmara Sea, are also of concern. The Marmara Sea segment may be locked, and could potentially host a large magnitude event.

“People in Istanbul are also on high alert, newly reminded of the seismic hazard that looms over them, with the knowledge that buildings in the area may not be trustworthy,” says Judith Hubbard, geologist and visiting assistant professor at Cornell University, who was not involved with the recent article.

The Dead Sea Fault system is another nearby concern, with a long historical record of infrequent but large earthquakes. A northern segment of this fault had three large earthquakes in the past 2,000 years between AD 100 and 750 and has now gone 850 years without a significant earthquake. Political and social turmoil in the region might make it difficult for necessary retrofitting and repair to ensure safer buildings before that next large event arrives. “After an earthquake there are always some international aid efforts, but the biggest payoff would be work before the next big earthquake,” says Hubbard.

Reducing vulnerability and building resilience

To better prepare for future hazards, Dal Zilio has several suggestions to lessen the impact of future large quakes and aid in recovery: update and enforce building codes to make new construction perform better in a strong earthquake; prioritize the retrofitting of older buildings; launch public awareness campaigns to inform residents of how to protect themselves and their property; and improve emergency response services. Promoting hazard insurance — which is required in Turkey — might be another way to help residents recoup their losses and recover more quickly. Dal Zilio also suggests investing in more research for early warning systems, and encouraging collaborations among urban planners, seismologists and residents to build seismically safer cities.

“Understanding why some earthquakes are particularly devastating is important, but often earthquake science remains divorced from human impacts,” says Hubbard. She adds that while earthquake science mostly focuses on understanding faults, “in the wake of a large earthquake, it is really important to think about why the science matters to people.”

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