Reflections on the Turkish-Syrian Earthquakes of 6th February 2023: Building Collapse and its Consequences
By David Alexander, on 9 February 2023
An interesting map was published by the US Geological Survey shortly after the Turkish-Syrian earthquakes.1 It showed (perhaps somewhat predictively) that there was only one tiny square of the vast affected area in which Modified Mercalli intensity (which is largely a measure of damage) reached 9.0, the ‘violent’ level.2 This is–just about–enough to damage very significantly a well-engineered structure (but not necessarily enough to bring it crashing down). Although the disaster of 6th February 2023 produced, in fact, stronger shaking than this, it should not have caused 5,500 large buildings to collapse. The disaster in Turkey and Syria is very obviously the result of poor construction. This is painfully visible in the video images of buildings collapsing. The patterns of collapse are also the same as those in the last 20 Turkish earthquakes, although they are doubtless more extensive this time around.
Building codes in Turkey have been upgraded five times in the last 55 years and are now perfectly good enough. The tragedy lies in their non-observance and the paucity of retrofitting. It is a mixture of simple errors, lax procedures, ignorance, deliberate evasion, indifference to public safety, untenable architectural fashions, corruption and failure to enforce the codes. Many, perhaps most, people in Turkey live in multi-storey, multiple occupancy reinforced concrete frame buildings. It is these that collapse. Most of them are highly vulnerable to seismic forces. There is plenty of engineering literature on the typical seismic performance defects of such buildings in Turkey. Perhaps we can grant a small exception for Syria, although before the civil war it did have building codes and earthquake research. However, the comment by a leader of the Syrian Catholic Church that buildings had been weakened by bombardment was something of a red herring. This probably affected about 2-3% of those that collapsed.
To know whether a reinforced concrete building is safe to live in would require knowledge of:
- the shear resistance (i.e., quality) of the concrete
- the presence or absence and connectivity of shear walls
- whether there are overhangs or other irregularities of plan that distribute the weight of the building unevenly or concentrate load on particular parts of it
- the presence or absence of a ‘soft-storey’ open ground floor which concentrates the load above columns that cannot support it during seismic deformation
- the connections between beams and columns, especially how the steel reinforcing bars are bent in
- whether there are proper hooks at the end of rebars on concrete joints
- whether the rebars were ribbed or smooth
- the quality of the foundations and the liquefaction, landslide or subsidence potential of the underlying ground
- the state of maintenance of the structural elements of the building
- any subsequent modifications to the original construction.
An experienced civil engineer could evaluate some of that by eye, but much of the rest is hidden and only exposed once the building collapses. A short bibliography of sources is appended at the end of this article.
Many of the news media that have reported the disaster have presented it as the result of inescapable terrestrial forces. While that cannot be negated, it is less than half of the story. The tragedy was largely the result of highly preventable construction errors. Vox clamantis in deserto: to examine this aspect of the disaster one would have to face up to difficult issues, such as corruption, political decision making, people’s expectations of public safety, fatalism versus activism, and more. How much simpler to attribute it all to anonymous forces within the ground!
A well-engineered tall building that collapses will leave up to 15% void spaces in which there may be living trapped victims. It was notable that, in many buildings that pancaked in Turkey and Syria, the collapses left almost no voids at all, thanks to the complete fragmentation of the entire structure. This poses some serious challenges to search and rescue. In some cases the collapse was compounded by foundation failure, leading to sliding or rotation of the debris.
There was also an interesting dichotomy in the images on television between the “anthill” type of urban search and rescue, carried out by people with no training, no equipment and no idea what to do, and professional urban search and rescue (USAR), which sadly was in the minority of cases. Nevertheless, it remains true that the influx of foreign USAR teams is, sadly, both riotously expensive and highly inefficient, as they tend to arrive after the ‘golden period’ of about 12 hours in which people could be rescued in significant numbers.
Among the damage there is at least one classic example of the fall of a mosque and its minaret, the same as that which happened in the Düzce earthquake of 1999. Mosques are inherently susceptible to collapse in earthquakes: shallow arches, barrel vaults, rigid domes and slender minarets. The irony is that the great Turkish architect of the 16th century, Mimar Sinan (after whom a university in Istanbul is named) had the problem solved. He threaded iron bars through the well-cut stones of his minarets, endowing them with strength and flexibility. It is also singular that one of the first short, stubby minarets in Turkey (located in Izmir) was built 300 years after Sinan died in 1588.
Select Bibliography of Sources on Turkish R/C Construction Practices
Cogurcu, M.T. 2015.Construction and design defects in the residential buildings and observed earthquake damage types in Turkey. Natural Hazards and Earth System Sciences 15: 931-945.
Dogan, G., A.S. Ecemis, S.Z. Korkmaz, M.H. Arslan and H.H. Korkmaz 2021. Buildings damages after Elazığ, Turkey earthquake on January 24, 2020. Natural Hazards 109: 161-200.
Dönmez, C. 2015. Seismic performance of wide-beam infill-joist block RC frames in Turkey. Journal of Performance of Constructed Facilities 29(1): 1-9.
Erdil, B. 2017. Why RC buildings failed in the 2011 Van, Turkey, earthquakes: construction versus design practices. Journal of Performance of Constructed Facilities 31(3):
Korkmaz, K.A. 2009. Earthquake disaster risk assessment and evaluation for Turkey. Environmental Geology 57: 307-320.
Ozmen, H.B. 2021. A view on how to mitigate earthquake damages in Turkey from a civil engineering perspective. Research on Engineering Structures and Materials 7(1): 1-11.
Sezen, H., A.S. Whittaker, K.J. Elwood and K.M. Mosalam 2003. Performance of reinforced concrete buildings during the August 17, 1999 Kocaeli, Turkey earthquake, and seismic design and construction practise in Turkey. Engineering Structures 25(1): 103-114.
David Alexander is Professor of Risk and Disaster Reduction. He has conducted research on disasters since 1980. His main foci of interest are emergency management and planning, earthquake science, disaster epidemiology, and theoretical issues in disaster risk reduction.
Note from editor: We offer our commiserations to all those affected by the tragic events of this week. UCL staff and students can find support here. Find out where and how to donate to the earthquake appeal here.