Why did the earthquake in Turkey cause so much damage? Many buildings collapsed like pancakes

Mark Quigley is Associate Professor of Earthquake Science The University of Melbourne

Two major earthquakes have shaken Turkey more than 6,000 people died and unknown numbers injured or expelled.

The first quake, near Gaziantep near the Syrian border, had a magnitude of 7.8 and was felt as far away as the UK. The second occurred nine hours later on what appears to be an overlapping fault and registered a magnitude of 7.5.

In addition to the devastation, about 3,450 buildings have collapsed, according to the Turkish government. Many of the modern buildings have failed in a “pancake mode” of structural collapse.

Why is that happend? Was it simply the enormous strength and violence of the quake, or is the problem with the buildings?

Thousands of years of earthquakes

Earthquakes are common in Turkey, which lies in a very seismically active region where three subsurface tectonic plates are constantly rubbing against each other. Historical records of earthquakes in the region go back at least 2,000 years, to a quake in AD 17 that leveled a dozen cities.

The East Anatolian Fault Zone, where these earthquakes occurred, lies on the boundary between the Arabian and Anatolian tectonic plates, which are moving past each other at about 6 to 10 mm per year. The elastic strain accumulated in this plate margin is released by intermittent earthquakes that have been occurring for millions of years. The recent earthquakes are therefore not a surprise.

Despite this known seismic hazard, the region contains much vulnerable infrastructure.

Over the past 2,000 years, we have learned a lot about how to build buildings that can withstand even the tremors of major earthquakes. In reality, however, there are many factors affecting building practices in this region and others around the world.

Poor construction is a known problem

Many of the collapsed buildings appear to have been constructed of concrete without adequate seismic reinforcement. Seismic building codes in this region suggest that these buildings should be able to withstand strong earthquakes — where the ground accelerates by 30% to 40% of normal gravity — without suffering this type of catastrophic failure.

The magnitude 7.8 and 7.5 earthquakes appear to have produced tremors in the range of 20 to 50% of gravity. Some of these buildings therefore failed at vibration intensities lower than the “design code”.

There are known issues in Turkey and elsewhere in ensuring safe construction and compliance with seismic building codes. Similar building collapses have been observed in previous earthquakes in Turkey.

In 1999, a massive earthquake near Izmit killed around 17,000 and collapsed up to 20,000 buildings.

After a 2011 quake that killed hundreds of people, then-Turkish Prime Minister Recep Tayyip Erdogan blamed shabby construction for the high death toll, saying: “Communities, builders and regulators should now see that their negligence amounts to murder .”

reconstruction

Although Turkish authorities know that many buildings are at risk of earthquakes, it is still a difficult problem to solve. Many of the buildings are already constructed, and seismic retrofitting may be expensive or not considered a priority compared to other socio-economic challenges.

However, post-quake reconstruction may provide an opportunity for safer rebuilding. In 2019 Turkey passed new regulations to ensure buildings are better protected against vibrations.

As welcome as the new regulations are, it remains to be seen whether they will lead to real improvements in construction quality.

In addition to significant loss of life and damage to infrastructure, both earthquakes are likely to have caused a variety of environmental impacts, such as: B. broken ground surfaces, liquefied soil and landslides. These impacts can make many areas unsafe for reconstruction – so recovery efforts should also include planning decisions about what to build and where to reduce future risks.

For now, aftershocks are shaking the region and search and rescue efforts are ongoing. Once the dust settles, rebuilding will begin – but will we see stronger buildings to withstand the next quake, or more of the same?

This article is republished by The conversation under a Creative Commons license.