After the devastating earthquake that occurred on September 8 with its epicenter about 60 km from Marrakech (Morocco), a logical question may arise: could a similar earthquake occur in Spain?
Before answering it, it is worth making some qualifications. The damage caused by an earthquake does not depend only on its magnitude, but on other factors such as the depth of the focus or hypocenter, the distance to the population and, fundamentally, the vulnerability of the exposed structures.
Magnitude is a measure of the energy that is released on the geological fault where the rupture occurs. This energy propagates in the form of seismic waves and attenuates with distance. When the focus is superficial and there are neighboring towns, the waves are barely attenuated and reach the town with great amplitude, so it is affected by intense movements.
If the buildings are also vulnerable, with a high capacity to experience damage, then all the factors for a catastrophe come together.
This is precisely what happened in last Friday’s earthquake. The magnitude was 6.8, which is already a large earthquake. The focus was quite shallow, 18 km from the surface. And there were numerous towns in the epicenter area, with highly vulnerable masonry and adobe buildings.
Two destructive earthquakes per century
And returning to the initial question, in Spain we can expect earthquakes of magnitude between 6.5 and 7, especially on faults in the south and southeast of the Iberian Peninsula, associated with the same tectonic process as the recent earthquake in Morocco: the collision of Eurasian and African plates.
In the Baetics there are a good number of faults capable of generating earthquakes in that order of magnitudes. If these earthquakes have a superficial focus and are located close to towns, then they could be lethal. Because, although vulnerability is not as high as it can be in Morocco, we also have many masonry or concrete buildings with poor anti-seismic design, which are highly vulnerable. Perhaps we could speak of hundreds of deaths, depending on the exposure.
In fact, in the past, we have had – on average – two destructive earthquakes per century, from the 15th century to the present day, a period in which there is a complete report of historical seismicity. With the exception of the 20th century, in which no catastrophic earthquake occurred, which has caused us to lose awareness of the risk.
A non-negligible risk
In the 21st century, the Lorca earthquake occurred, which was moderate, with a magnitude of 5.1, but due to a confluence of the other factors mentioned, it caused nine fatalities and considerable material damage. This earthquake is far from being the maximum that can be expected in the south and southeast of Spain.
If we take into account that by increasing the magnitude by one degree, the energy is multiplied by 30, between an earthquake like the one in Lorca and one of magnitude 6.5 to 7, there would be a difference of almost 900 times in terms of energy. Without wanting to be alarmist, but realistic, we have a seismic risk that is not inconsiderable in Spain and we must prepare to face it.
It also happens that the last large and destructive earthquake took place in 1884. It was the Arenas del Rey earthquake (Granada), known as the Andalusia earthquake, with an estimated magnitude of around 6.8. That earthquake caused more than 1,000 deaths and since then no event of similar magnitude has occurred in Spain, except for two very deep ones that have not caused damage. Therefore, 140 years have passed without a major earthquake when on average we have had two per century. You could say that we are in injury time.
How can we prepare?
In this situation, there is no way to look the other way. Ignorance or lack of awareness makes us more vulnerable. If we want to avoid the catastrophe, preventive measures must be adopted and these must be implemented before the expected earthquake occurs.
The main measure is the appropriate earthquake-resistant design, regulated in our case by regulations from 2002 (NCSE-02), which must be renewed. And we should also have municipal emergency plans that guarantee quick and effective action in the event of an earthquake.
The safeguarding of human lives depends on action in the first 48 hours and for this to be effective, a plan must be designed that establishes, for example, possible evacuation routes, places where people who become homeless should be relocated or sizing of troops. necessary for the rescue and care of the injured.
In fact, the Basic Civil Protection Directive establishes the mandatory nature of such plans in all the municipalities of Andalusia, Murcia, a large part of the Valencian Community and Catalonia and some of other autonomous communities. But there are very few towns that have already designed this plan, which is the responsibility of municipalities and public administrations. Because? Because generally seismic risk is not considered a priority.
In the four-year period that a mandate lasts, those responsible do not think that “they are going to have to” deal with the seismic phenomenon and they are dragging their feet in developing the well-known emergency plans. But there is a paradox that the more time that passes since a major earthquake, the lower the social awareness and the greater the probability that another one will occur in the area.
However, the day after the earthquake many measures will be taken, which will obviously no longer be preventive, and the probability will have decreased drastically.
The message therefore is “let’s not wait for D-Day”, let’s use all the means at our disposal so that the earthquake that is going to occur is not a catastrophe. Because the earthquake is a natural phenomenon, but the catastrophe is not natural. This can be avoided with appropriate preventive measures and immediate action after the event. The Marrakech earthquake, which has caused so much damage and desolation in the neighboring country, should be a warning to minimize this risk in Spain and any other country with seismic risk.