Learning from the earthquake in Turkey

When a cataclysmic event like the Turkey earthquake occurs, as engineers our reflection cannot end with mourning the more than 40,000 dead and contributing to the aid relief effort. In the aftermath, what we see is a hard but critical lesson for structural engineers, builders, urban planners and the authorities that oversee seismic safety standards for buildings and infrastructure.

These lessons need to be integrated rapidly into our practices, particularly to inform rebuilding efforts across Turkey and Syria to house the hundreds of thousands of people left homeless and reconstruct the social and commercial centres. It would be hoped that what is reconstructed is safer and more resilient, and that the lessons of the quake are applied more broadly in all regions where tectonic events are likely.

Let’s start with the geophysics

On 6 Feb 2023, a series of earthquake occurred in southeast of Turkey, the area is known to be seismically active, as it is located at the intersection of three tectonic plates.

The recorded epicenter of the quake was close to Gaziantep, with its hypocentre at 10miles (16km) from the surface. The first earthquake with magnitude 7.8 happened at 4:17am local time. A series of aftershocks with magnitude 6.5 followed until another large earthquake with magnitude 7.5 occurred at around lunchtime.

The peak ground acceleration (PGA) of the first mainshock reached to around 0.7g, with the spectral acceleration exceeded 2g around 0.5-0.6 seconds. To put it into perspective, any buildings with a vibration period of 0.5s to 0.6s would experience maximum lateral force as much as two times its own weight!

This was followed by a series of high magnitude earthquakes, and resulted in total collapse of many older buildings, as well as some new buildings. It had the highest death toll of any earthquake in the past century

Surveying the damage

There was a significant quantity of video footage available on the internet including video shot during the quake, and videos showing the aftermath. Many buildings were entirely flattened – demolished in a matter of moments by the interacting forces of physics.

I noticed that some buildings collapsed in a sudden structural failure event at ground level, with no visible major failure at the upper floors. These buildings collapsed suddenly from the bottom-up, and this is particularly concerning because in these cases of brittle failure, there is no time for either the occupants or people in the immediate vicinity to escape.

Asking the difficult questions

As a structural engineer, damage at this scale raises many questions for me, such as why was the extent of the damage so great? What went wrong in the design and construction of some buildings that made them prone to brittle failure? And most importantly, how can we do better?

A phrase we hear often is, earthquakes don't kill people, buildings do.

Maybe the earthquake magnitude was the problem?

Earthquake-resistant structural design is based on the seismic hazards of a specific region. This is derived from data about earthquakes recorded in the past and also analysis of the specific plate tectonics and fault line interactions in an area.

Because the degree of risk is based on what has been known to occur in the past, and the behaviour of plate tectonics and subsurface geophysics is difficult to predict with accuracy, it is genuinely impossible to know if we are designing for the largest earthquake possible.

However, this is not the end of the story, as designing a building is much more than just making it ‘strong enough’!

What do we mean by ‘earthquake-resistant’?

According to Eurocode 8, the main purpose of earthquake-resistant building design is: (1) Human lives are protected, (2) Damage is limited, and (3) Structures important for civil protection remain operational. These are achieved through the design and detailing criteria set out in the code, resulting in types of failure which are ductile and thus avoid any sudden collapse, to enable people to escape.

The focus is not only designing a building that can resist the loading required, but also to control its damage or failure in extraordinary cases.

It is similar to the principles of design for a car’s bonnet or hood. In a car crash, this part is designed to get crushed (crumple zone) and absorb the impact energy, minimising the danger to the occupant, who is protected within the safety cage.

In the building context, one design method is called “strong column, weak beam” which means the design of the column should be stronger than the beam, so the beam will absorb any damage before the column. The beam becomes the sacrificial part in the form of plastic hinges, which is ductile and would prevent instant failure to the whole structure.

There are other methods such as using shear walls, braces, and bearings, where these elements are designed to absorb the damage in the first instance, giving occupants more time to safely exit the building and saving lives.

The major lesson for a structural engineer

As structural engineers, we are very good at designing our structures to be stiff and strong enough to resist any loading required by the design standards. However, we need to ask ourselves, have we taken a deeper look into our design and the context in which it will be delivered? If something beyond our design happens, how would the structure behave? Is there a risk of sudden failure, or will it be able to absorb damage to some degree before it catastrophically deteriorates, giving people a chance to escape?

Designing building structures is ultimately about much more than just physics and materials. It requires us to also think about how we provide spaces where people know they are safe and secure, even at unexpected times. This is a responsibility we must take seriously to avoid having tragedy repeat itself.