Two large earthquakes have struck Turkey, leaving thousands dead and injured or displaced.
The first quake, near Gaziantep, along the Syrian border, had a magnitude of 7.8 and was felt as far as the UK. The second occurred nine hours later, on what appears to be a transverse fault, and registered a magnitude of 7.5.
In addition to the devastation, according to the Turkish government, some 3,450 buildings have collapsed. Many have failed in a “pancake mode” of structural collapse.
Why did this happen? Was it simply the sheer magnitude and violence of the quake, or is the problem with the buildings?
Thousands of years of earthquakes
Earthquakes are frequent in Turkey, which is in a very seismically active region where three tectonic plates are constantly colliding with each other under the Earth’s surface. 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 relative to each other at a rate of about 6 to 10 mm per year. The elastic stress that builds up in this plate boundary zone is released by intermittent earthquakes, which have occurred over millions of years. So the recent earthquakes are not a surprise.
Despite this known seismic hazard, the region contains much vulnerable infrastructure.
In the last 2,000 years we have learned a lot about how to build buildings that can withstand the shocks of even severe earthquakes. However, there are actually many factors that influence building construction practices in this region and in others around the world.
Poor construction is a known issue
Many of the collapsed buildings appear to have been made of concrete without adequate seismic reinforcement. The seismic building codes of this region suggest that these buildings should be able to withstand strong earthquakes (in which the ground increases normal gravity by 30% to 40%) without suffering this type of collapse.
The 7.8 and 7.5 quakes seem to have caused shaking of the order of 20 to 50% of gravity. Thus, a portion of these buildings failed with shaking intensities below “design code”.
There are well-known problems in Turkey and elsewhere in ensuring the safety of building construction and compliance with seismic building codes. Similar building collapses have been observed in previous earthquakes in Turkey.
In 1999, a major earthquake near Izmit caused 17,000 deaths and the collapse of up to 20,000 buildings.
Following a 2011 earthquake that killed hundreds of people, Turkey’s then Prime Minister and now President Recep Tayyip Erdogan blamed poor construction for the high death toll, saying: “Municipalities, builders and supervisors should now see that their negligence amounts to murder.”
Reconstruction
Although the Turkish authorities know that many buildings are unsafe in the event of an earthquake, it remains a difficult problem to solve. Many of the buildings are already built, and seismic retrofitting can be expensive or not considered a priority compared to other socio-economic challenges.
However, post-earthquake reconstruction can be an opportunity to rebuild more safely. In 2019, Turkey adopted a new regulation to ensure that buildings are better equipped to withstand shocks.
While the new standards are welcome, it remains to be seen whether they will translate into real improvements in build quality.
In addition to significant loss of life and damage to infrastructure, both earthquakes are likely to have caused a myriad of environmental effects, including ground rupture, soil liquefaction, and landslides. These effects can make many areas unsafe to rebuild, so rebuilding efforts must also include planning decisions about what can be built and where to reduce future risks.
For now, aftershocks continue to shake the region and search and rescue efforts continue. Once the situation settles, the reconstruction will begin, but will we see stronger buildings, capable of withstanding the next earthquake, or more of the same?
With information from The Conversation (CC 4.0)