Earthquake in Turkey is not new for the Mediterranean

The Mediterranean is a region where, as we know, devastating earthquakes have occurred for several thousand years. Greece, Turkey, Italy, Egypt, Algeria, and even southern Spain, among other countries, at some point experienced strong earthquakes with hundreds or thousands of victims.

This is a complex area from a tectonic point of view, due to the fact that different tectonic plates converge in it. Essentially, the Eurasian Plate bounds and collides with the African Plate (today it is preferred to be called the Nubia Plate) at rates that fluctuate between 4 mm per year in the western sector – around the Alboran Sea – and 10 mm per year in the western sector. eastern sector, in the eastern Mediterranean. This is a process that began about 50 million years ago.

These speeds, which may seem extremely small to us, are not at all like that from a geological point of view. Moreover, they are the source of deformations that gradually occur in the outermost part of the Earth, the lithosphere, and which cause the accumulation of elastic energy, which, when the time comes, is released by an earthquake.

When one approaches this area, one notices that this limit is difficult. It shows areas where one of the plates goes under the other, in what we call the subduction zone – in Italy, Greece and Cyprus – and others where it slides horizontally relative to the other in the so-called 4th rupture. Examples of the latter case are the Dead Sea faults passing through the Sinai Peninsula, Israel and Lebanon; the North Anatolian Fault, which runs through all of northern Turkey, and the East Anatolian Fault, which runs along southeast Turkey and may have caused the February 6 earthquake. These two faults, passing through this country in its northern and southeastern parts, are pushing Turkey towards the Mediterranean Sea, towards Greece.

Earthquakes in the Mediterranean

Defects tend to store elastic energy, as a wooden stick does when we take the ends with both hands and bend it, in some cases for decades, in others for hundreds of years. When the time comes, due to the resulting gap, they are able to cause strong earthquakes, which often lead to a significant number of casualties and destruction.

The Ibero-Mogreb region, in which Spain is located, has suffered from strong earthquakes in historical times, as well as in the recent past.

We can refer to the earthquakes in Oran (Algiers) in 1790, when some historical accounts speak of the complete destruction of the current historical part of the city, which claimed the lives of almost 3,000 people. In 2003, in a suburban town near the capital of Algeria, a magnitude 6.8 earthquake claimed more than 2,000 lives and 10,000 injuries.

Morocco has experienced devastating earthquakes such as the Fez earthquakes of 1624 and 1755, or the recent 1994, 2004 and 2016 quakes in the El Hoceima region, with magnitudes of 6.0, 6.4 and 6.3 respectively.

In Spain, we can cite the Arenas del Rey earthquake in Granada, which occurred on Christmas Day 1884 and killed between 1,000 and 1,200 people. The most recent of these is Lorca (Murcia) in 2011. Although it had a magnitude of only 5.1, nine people died, more than 300 were injured, and more than 1,100 houses had to be demolished.

Earthquakes kill, buildings do too

The effects caused by an earthquake are mainly related to two factors: the characteristics of the earthquake and the quality and design of the buildings.

Regarding the first, the magnitude, duration, distance and depth of the earthquake have a fundamental influence. Larger magnitude means more energy or, equivalently, more amplitude of the waves generated by an earthquake. The duration of the fault rupture implies a greater or lesser time of impact on buildings or infrastructure.

Distance and depth are also important. The closer and smaller the earthquake, the stronger its consequences. The same thing happens with the explosion: the further it happens, the less it will affect us.

But there is also a very important factor, in some cases the most independent of the earthquake: the quality and design of buildings and infrastructure.

In seismic, we work with the principle that earthquakes do not kill people, but buildings. In seismically active areas where we know and expect that there will be major earthquakes in the future, it is critical to design buildings to withstand the ground vibrations that these earthquakes will cause. In principle, even if they fail in an earthquake and are seriously damaged, we should at least design them so that they do not collapse.

What do we know about earthquakes?

Today, we do not yet know how to predict when the next earthquake will occur and how strong it will be. Leading seismologists are of the opinion that this will never happen. In many cases, we know where they will occur.

We know which faults are the most important, which usually caused major earthquakes in the past, and in some cases we also know something about their behavior. This is what we might call a long-term forecast.

With this information, researchers working on seismic hazards can provide in each area the ground motion values ​​we expect to occur in the future, thus improving the earthquake engineering standards in each country.

Urban planners need to use this information to be truly effective, for example when designing buildings, selecting space for expansion in a city, or tightening building codes for basic infrastructure.

José A. Pelaez Montilla, Professor of Earth Physics, University of Jaén

This article was originally published on The Conversation. Read the original.

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