Granada has registered this Tuesday, August 18, an earthquake of magnitude 4.8 with epicenter northwest of Gójar, at 10:37 hours. The tremor occurred just three days after another earthquake of identical magnitude located near Alhendín during the early morning of Saturday.
The catalog of the National Geographic Institute also records numerous subsequent movements: one of magnitude 3.9 near Churriana de la Vega, another of 4.2 in Alhendín, and a third of 4.0 in Ogíjares.
The succession of tremors does not respond to an exceptional or unknown cause. Granada is located over one of the areas with the highest seismic activity in the Iberian Peninsula, where the movement of tectonic plates, a network of active faults, and a terrain capable of intensifying the tremors converge.
Africa and Eurasia are approaching at up to five millimeters per year
The origin of the problem lies in the movement of the African and Eurasian plates. Both are approaching at a rate of between four and five millimeters annually, according to studies by the University of Granada and the Andalusian Institute of Earth Sciences.
Although that distance may seem insignificant, pressure accumulates over the years in the Earth's crust. When the rocks can no longer withstand it, they shift abruptly along the faults and release energy in the form of an earthquake.
The province is part of the Betic mountain ranges, located in a broad contact zone between both plates. On the surface of the Granada basin, this complex interaction generates active faults that fragment the subsoil and favor recurring earthquakes.
The Vega de Granada is crossed by active faults
The seismic activity is not concentrated in a single fracture. Beneath Granada and its metropolitan area, there exists a network of faults that affects municipalities such as Atarfe, Santa Fe, Alhendín, Gójar, and Ogíjares.
Researchers from the University of Granada explain that the movement of one fault can alter the equilibrium of nearby ones and provoke a chain reaction. This helps to understand why different localities register tremors with only a few minutes or hours of difference.
However, identifying the specific fault responsible for each earthquake requires a specific analysis. The proximity between several epicenters does not allow automatically attributing all movements to the same fracture.
The recent activity also did not start this Tuesday. The Andalusian Institute of Geophysics of the University of Granada recorded on July 26 another earthquake of magnitude 3.7 near Alhendín, with a depth of 4.6 kilometers.
More than 3,000 earthquakes in the sequence of 2020 and 2021
Granada has already experienced prolonged episodes of seismic activity. An official report from the National Geographic Institute on Atarfe and Santa Fe counted 3,079 earthquakes between December 2020 and August 2021.
Of all of them, 353 were felt by the population, 36 reached or exceeded magnitude 3 and six reached at least magnitude 4.
A subsequent investigation by the University of Granada determined that that sequence was related to a fault segment of approximately two kilometers located under Santa Fe, between three and five kilometers deep.
The nearby faults then acted as barriers and limited the propagation of the rupture. However, this conclusion specifically refers to the 2021 episode: it does not mean that all future earthquakes in Granada will behave the same.
Are they aftershocks or a seismic swarm?
After a significant earthquake, aftershocks may occur as the ground readjusts the accumulated stresses. Another possibility is a seismic swarm, characterized by numerous tremors close to each other without necessarily having a single clearly dominant main movement.
The succession of earthquakes in these days still requires a detailed analysis to determine what pattern it follows. The existence of several nearby earthquakes is not enough on its own to confirm that Granada is going through a seismic swarm. In any case, the experience of 2021 shows that these sequences can last for weeks or months, although their evolution and intensity are not precisely predictable.
Why some earthquakes are felt so intensely
Magnitude is not the only factor that determines the effects of an earthquake. Depth, distance to the epicenter, terrain characteristics, and building resilience also play a role.
When an earthquake originates at shallow depth, seismic waves travel less distance before reaching the surface. For this reason, a moderate and shallow movement can be felt strongly in densely populated areas.
This is joined by the composition of the Vega, formed in part by sediments capable of amplifying vibration. A study published in 2024 by a researcher from the Andalusian Institute of Geophysics analyzed this phenomenon in the Granada neighborhood of La Chana.
The research detected indicators of spectral amplification of up to 6.5 at specific points. This does not mean that all earthquakes multiply their intensity by six in Granada: it indicates that certain characteristics of the subsoil can increase the seismic response in some locations and buildings.
Could there be a larger earthquake?
The historical record confirms that the province can experience earthquakes greater than the current ones. The National Geographic Institute attributes to the earthquake of Arenas del Rey in 1884 an estimated magnitude of 6.5 and between 750 and 900 fatalities.
However, that precedent does not allow us to conclude that a similar episode will occur now. The IGN itself reminds that there is no method capable of predicting with precision when, where, and with what magnitude the next earthquake will occur.