shallow depth of epicenters is a major reason why they have been so devastating

The earthquakes that hit Turkey and Syria in the early hours of February 6 caused terrible devastation on a scale not seen in Europe for decades. At the time of writing, the death toll has risen above 11,000 people and will continue to rise in the coming days and weeks. Hundreds of thousands of others have lost their homes.

There are many reasons why the death and devastation have been so terrible. First and foremost, the magnitude of the two major events and their associated aftershocks. These earthquakes, measuring 7.8 and 7.5 on the moment magnitude scale, each released about as much energy as the largest atomic bomb test ever conducted during the Cold War—about 50 megatons, in 1961, by the former Soviet Union. And there were two of these events in the same region, separated by a matter of hours.

To this we must add the clusters of aftershocks that follow the main events. These are smaller (usually below magnitude 5) but will last for several days, gradually decreasing in intensity and regularity. They are nevertheless dangerous, as buildings that are already severely weakened by previous events can collapse. This inevitably complicates rescue efforts in the region.

Another factor is the timing of the first and largest earthquake. It happened at 4:17 a.m. local time, when most people would have been asleep at home. In an earthquake, the vast majority of victims are not caused by the shaking, but by the collapse of buildings. The timing of this event was as bad as it got – people probably had very little chance of escaping their homes in time. This is probably an important factor in the very high number of deaths and injuries.

Read more: Earthquakes between Turkey and Syria: A seismologist explains what happened

Depth charge

But a major geological contributor to the devastation was the relatively shallow depth of the quake’s epicenters: 18 km for the first 7.8 shock and 10 km for the later 7.5 shock. Worldwide, these are relatively close shocks. There are two reasons why this leads to a greater degree of destruction.

Simply put, the first reason is that the shallower an earthquake is, the closer the Earth’s surface is to the epicenter. This means that the shaking of the ground is more intense and destructive. There is less chance for the shock waves to dissipate, as happens when earthquakes happen deeper in the Earth and they travel through tens of kilometers of rock.

The second reason is that the faults that cause earthquakes greater than 5.5 are more likely to break through to the surface. This creates – almost immediately – a ground displacement in which part of the ground literally shifts a few meters in relation to an adjacent part.

These surface faults – also called “capable faults” – are incredibly damaging. They can lead to the cutting of major underground and above-ground infrastructure, including water pipes, electricity cables, gas pipelines and tunnels.

There are already reports of damage to pipelines in Turkey after the events of February 6. Spectacular satellite and ground-based photos also appear of shifted roads and rail lines, as well as severe damage to buildings that straddle the faults. All this is in addition to damage caused by shaking, liquefaction of soft sediment in valleys and landslides.

Three-metre-long break in a road caused by the 2023 Turkish earthquake.

A three-meter rupture in the Kahramanmaraş-Gaziantep highway, close to the village of Tevekkelli in the earthquake zone. Hasan Sozbilir/Eskisehir Osmangazi University, Author provided

In a recent blog, Professor Hasan Sözbilir of the Dokuz Eylül University Earthquake Application and Research Center studied the region and reported: “As far as I can see, at least three fracture segments have broken. The total length of the surface fault is more than 500 km.”

So why were these events relatively shallow in this region? Some of the largest earthquakes known to have occurred are associated with the so-called “Pacific Ring of Fire”. These earthquakes are usually generated at depths of up to 700 km as the strong, dense oceanic plates plunge deep beneath the surrounding continents.

However, Turkey lies in a region of weaker, mostly continental lithosphere where the crust is only about 30 km thick, close to a point where three tectonic plates meet – Africa, Arabia and Anatolia. The convergence of the Arabian Plate is pushing the wedge-shaped Anatolian Plate westward, creating a series of subvertical, strike-slip faults, such as the East Anatolian Fault, which failed during the magnitude 7.8 event.

Map showing the action of tectonic plates near the Turkey/Syria earthquake

In such continental crust, the strongest part – and the most likely point for the origin of large earthquakes – is typically between 10 km and 20 km depth. So in these types of environments, shallow, surface-rupturing faults are more likely to form.

Wrong time, wrong place

A third factor is simply that the region where the earthquakes occurred is densely populated. Considering the timing, significant loss of life is almost inevitable after an event – ​​or events – of this magnitude.

Deadly earthquakes are known in Turkey. In the past 50 years, there have been at least four major events with significant loss of life – in 1975, 1983, 1999 and 2020. After the 1999 Izmit earthquake, Turkish authorities made serious efforts to improve construction standards to withstand earthquakes .

But there are limits to what you can do in a densely populated area with events of this magnitude. And we should not forget that the two main seismic shocks may have been more than twice the size of the largest known historical earthquake in the region.

In addition, in Syria, we should add that years of ongoing civil conflicts have significantly degraded construction infrastructure, making the event in the region less resilient to the effects of seismic tremors. This is also likely to hamper efforts to provide assistance and relief and, in the longer term, reconstruction.

Read more: Turkey-Syria earthquake: how disaster diplomacy can bring warring nations together to save lives

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Bob Holdsworth does not work for, consult with, own stock in, or receive funding from any company or organization that could benefit from this article, and has not disclosed any relevant connections outside of their academic tenure.

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