When we talk about earthquakes there is usually a terminology that can sometimes be confusing for the average population. In this case, we are going to talk about the term seismic swarm. It is a term that is widely used when these events occur and many people do not know what it means.
For this reason, we are going to dedicate this article to telling you what a seismic swarm is, what its characteristics are and how important it is to know it.
What is a seismic swarm
A seismic swarm is a group of nearby earthquakes, of a certain magnitude, that occur one after the other over time, rather than each following a pattern of one large earthquake and several smaller aftershocks.
The more or less rigid plates on which the continents reside float above the hot, viscous asthenosphere at the top of the mantle. By pressing one on top of the other, earthquakes happen, but not only because of that.
In the case of Grenada, The zone affected by the seismic swarm is given by a set of extensive faults that have accumulated energy and that have been preceded by earthquakes.
Are multiple small earthquakes better than one large earthquake with aftershocks? In general, from a destructive point of view, yes. In terms of energy, since the scale is logarithmic, growth is rapid. It takes many small magnitudes to equal one large magnitude. Many earthquakes of magnitude 4,5 mean earthquakes less energetic than those of magnitude 5.
Today, scientists talk about the moment magnitude (MW) scale. In Europe, 4,5MW and V-VI are "very strong", as is the strongest case in Granada. When a big earthquake happens, it never happens alone. There are always adjustments. Those who follow it reduce their intensity, which is normal. Of course, the destructive power of an earthquake is not only related to the intensity of the vibration of the source, but also with the depth and distance from the source.
How long does the earthquake swarm last?
It is difficult to predict how long an earthquake swarm will last since earthquakes are very difficult to predict. It will take as long as small earthquakes last along with their aftershocks. The southern part of the peninsula is located at the point of contact of two large tectonic plates: the eurasian and african plates. From that friction, the African plate pushes and accumulates energy.
The nature of each earthquake is different, but in Spain it is usually related to faults, cracks in the earth's crust that release energy. This is completely normal. It has been happening and it will continue to happen. Africa pushes about 4 or 5 millimeters a year towards the peninsula.
The so-called Iberian microplate is under pressure from the large Nubian plate (where Africa is located), which is moving northwest, but not very fast. This activity involves folding and faulting. But we don't have a very clear plate boundary, a belt of tectonic activity of about 600 kilometers.
In the eastern part of the peninsula, closer to Granada, Almería and Murcia, it can be said that the land stretches or tears. In the west, in Cádiz and the Algarve, it is compressed. The convergence between these two plates began about 40 million years ago and continues today. Little by little, they will make the Mediterranean disappear. In about 50 million years, the great mountain range that spans what is now southern Europe will take its place.
Southern Spain is geodynamically complex. The largest earthquake on the peninsula occurred in Granada, but it was at a depth of up to 600 km. In 2010 there was a magnitude 6,4, but hardly anyone noticed because it was so deep. There is no scientific basis for expecting a major earthquake in Grenada.
Can earthquakes be predicted?
The short answer is no. However, thanks to risk maps, hazard studies and historical series, we know where they will occur, but it is not known when. If we compare it with the weather forecasts, here we see the numerous observations we make of the atmosphere (satellites, probes, continuous measurements at a distance and in situ...). Under our feet, however, we lack vision and a similar number of sensors. In addition, earthquakes obey very diverse phenomena.
In Granada, the last major earthquake occurred in the city of Arenas del Rey in 1884. 106 localities were affected, of which 39 were seriously affected. It completely destroyed the Arenas del Rey and the Ventas de Zafarraya, they had to be rebuilt.
What is to be done?
According to the General Directorate of Civil Protection:
If you are inside a building, make sure you:
- Seek shelter under a lintel or some sturdy furnituresuch as a table or desk, or near a main pillar or wall.
- Stay away from windows, glass doors, cabinets, dividers, and objects that could fall and hit you.
- Don't use the elevator.
- Use lanterns for lighting and avoid candles, matches or flames of any kind.
If the earthquake surprises you abroad, you should:
- Move to open areas, away from damaged buildings.
- Try not to go near or enter damaged buildings. The biggest danger is the vertical orientation of the facade.
- if you drive, it is recommended to stay in the car and stay away from bridges, utility poles, dilapidated buildings, or landslide areas.
- At a constructive level, if you live in an area of seismic risk, a series of precautions are recommended: Control what comes down first: the chimney or the eaves and supply lines. Inside the house you have to properly secure heavy and fragile items, and store toxic or flammable items.
Following the devastating 2011 Lorca (Murcia) earthquake, ICOG drafted the Ten Commandments aimed at minimizing earthquake damage in Spain, calling for constant updates to earthquake-resistant building standards.
As you can see, a seismic swarm can be dangerous if precautionary measures and action are not taken. I hope that with this information you can learn more about what a seismic swarm is, its characteristics and danger.