ANU experts explain the seismic, social and structural factors that contributed to the death toll and destruction.

It is clear now that the magnitude 7.8 earthquake that struck Türkiye and Syria on Monday 6 February 2023 has caused significant devastation. This has been compounded by several large aftershocks and secondary events in the region, such as the magnitude 7.5 event that occurred just nine hours later. At the time of writing, more than 12,000 deaths have been reported, but this number is likely to rise.

How big was the quake?

Earthquakes of this size are relatively rare; over the last 10 years only 23 earthquakes of magnitude 7.8 and above have occurred anywhere in the world. Most of these have happened in subduction zones — where two tectonic plates collide and one sinks into the mantle underneath the other— and not all have caused the same level of destruction as seen this week.

The event impacting Türkiye and Syria is significant because it occurred in a different type of tectonic setting, a transform plate boundary on a continent, where people live. It is also the largest earthquake ever instrumentally recorded in the region. However, it’s not the biggest earthquake ever in the region: historical records indicate that earthquakes of comparable size have likely occurred in this region in the past, most notably a large earthquake in 1114 AD that struck in a similar location. 

Citizens of Hatay Antakya, Türkiye, on 7 February 2023, one day after the earthquake as rescue efforts continue in the wreckage of destroyed buildings. Photo: ZUMA Press Inc./Alamy Stock Photo

Why did the earthquake occur here?

The earthquake and secondary events occurred at the boundary between the tectonic plates of Anatolia and Arabia. To the south, Arabia is pushing northwards. Anatolia is blocked to the north by the continent of Eurasia, and is squeezed westward out into the Mediterranean. This scenario has resulted in the formation of the East Anatolian Fault Zone that runs through south-eastern Türkiye, where the recent earthquake occurred. The relative motion of the two tectonic plates (Arabia to the north-east, Anatolia to the south-west) built up stress at the fault zone over centuries, which was finally released when a fault broke and caused the earthquake.

The fault zone is not a single fault, but made of multiple fault strands. The first earthquake of 6 February probably ruptured about half of the entire length of the main fault strand based on the distribution of aftershocks so far (see figure below). The magnitude 7.5 earthquake nine hours later, however, ruptured a second strand further north, and was probably triggered by stresses caused by the first quake.

Location of mainshocks (red circles) and aftershocks that have occurred in Türkiye since the magnitude 7.8 earthquake. Figure: European-Mediterranean Seismological Centre (EMSC).

Why was this earthquake particularly devastating?

There are several factors that make some earthquakes more damaging than others. The size of the earthquake is just one of them. The larger the magnitude the more intense the seismic shaking and the more energy that is released. This increases by a factor of 30 for every magnitude step, so a magnitude 7 event releases 900 times more energy than a magnitude 5. The magnitude also scales with the length of the fault that ruptures. In this case, the rupture length appears to be more than 200 km long with intense shaking experienced all along it, not just at the epicentre point.

Other factors that contribute to devastating events are the depth of the earthquake, its proximity to population, and most importantly, the standard of building construction. There is a common phrase, “earthquakes don’t kill people, buildings do”. Unfortunately the recent event in Türkiye and Syria appears to be the perfect storm of all these factors.

The United States Geological Survey reported that the magnitude 7.8 earthquake originated at a relatively shallow depth of 17.9 km, which falls within the outer layer of the Earth — the crust. With only a short distance to travel to reach the surface, this allowed seismic waves generated by the earthquake to maintain much of their initial energy.

The earthquake also hit a densely populated area. For the magnitude 7.8 event it’s estimated that more than five million people live in the VII zone of ‘Very Strong’ shaking or higher, according to the Modified Mercalli Intensity Scale. At this level damage is ‘negligible in buildings of good design and construction’ but ‘considerable in poorly built or badly designed structures’. Footage emerging from the scene shows buildings collapsing like pancakes, indicating that building codes have not been complied with.

Can we stop this happening again?

As rescue and recovery efforts continue, this earthquake is already one of the deadliest in recent history. We cannot stop large magnitude earthquakes from happening, but we can minimise the damage and deaths that result from them. Hopefully, we will learn from this disaster to be better prepared in similar earthquake prone parts of the world.

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