Why does the Vega de Granada tremble so much and the Sierra Nevada rises?

La Vega de Granada is a tectonic depression that has a long record of seismic activity throughout history, starting with the Santa Fe earthquake in 1431, which caused serious damage to the Alhambra.

Subsequently, there were destructive earthquakes in 1806 (Pinos Puente; M 5.3), 1956 (Albolote; M 5.0) and more recently, the seismic swarm of 2021, which affected the towns of Atarfe, Pinos Puente and Santa Fe with hundreds of small earthquakes (M 4.5) that bear witness to the important tectonic unrest in the area.

But why is this area the one with the highest seismic activity in the interior of the Peninsula? It turns out that the Granada area is located in the Betic Mountain Range, the youngest mountain system on the peninsula, a consequence of the collision between the African and Eurasian plates, whose relief began to rise about eight million years ago.

Furthermore, Granada and its plain are located at the foot of the Sierra Nevada, the highest mountain massif on the Peninsula (Mulhacén, 3842 m). There are coastal sediments from about eight million years ago (Miocene) in the Sierra Nevada at an altitude of 1830 m a.s.l. and in other nearby reliefs at just over 1980 m.

That is, during the last eight million years the mountain massif has risen a minimum of 2000 m and elevation rates of up to 1 mm/year, which continue today. But the process of geological elevation does not occur progressively and silently, it occurs "match by match", as Simeone would say:

This is earthquake by earthquake. Tectonic uplift is the product of the sum over time of the individual finite displacements that occur during each earthquake. The displacements in depth (< 10 km) of the normal faults during earthquakes of magnitude 4.5 - 5.5, which historically characterize the Granada plain, do not usually exceed a few meters, which translates to 2-4 cm on the surface (DinSar Data).

Since NW-SE Africa-Eurasia convergence rates in the Western Mediterranean are 2-4 mm/year, it takes quite a few years for metric strains to accumulate. When this happens, the Sierra Nevada grows a few millimeters and the Vega de Granada sinks another few millimeters.

The Sierra Nevada relief is located on the first shock line of the collision between the plates, there will continue to be earthquakes and it will continue to rise. The teenage growth spurt has passed, but from time to time we will have scares, some of greater importance.