Another 4.8-magnitude earthquake shook the southern Spanish city of Granada on Tuesday, the second in three days, along with 348 tremors since August 14th. Why is there so much seismic activity in this part of Spain?
Granada has experienced a series of terremotos (earthquakes) across the province since August 14th.
According to Spain’s National Geographic Institute (IGN), 348 tremors have been recorded since then.
This isn’t the first time the Andalusian province has experienced them either – between 2020 and 2021 around 3,000 small earthquakes were detected there. Five of them reached magnitudes between 4.1 and 4.5.
There was another larger earthquake in 2010 with a magnitude of 6.3 and there have been others recorded throughout history.
READ ALSO: Spain’s Granada rocked by another earthquake
While other areas in Spain also have a track record of quakes – Murcia, Alicante, Málaga and Almería, Huelva and Cádiz in particular – the majority seem to occur in Granada most recently.
So why is Granada at greater risk from seismological activity?
The meeting of the Eurasian plates and the presence of fault lines
According to seismologists, the Granada Basin is one of the most earthquake-prone regions on the Iberian Peninsula and has also experienced some of the strongest earthquakes in recorded history.
The National Seismic Network describes the area as “highly dangerous” because it has “many faults capable of generating earthquakes”.
One of the reasons for this is because Granada lies within the Betic Cordillera, which is Spain’s youngest mountain range. It’s also where the African and Eurasian plates meet. Not only that but the plates are growing towards each other at a rate of 4 to 5 millimetres per year, according to Jesús Galindo-Zaldívar, a researcher at the University of Granada.
READ ALSO: What to do in the event of an earthquake in Spain
Seismic swarms and the Sierra Nevada
Granada is home to the Sierra Nevada mountain range – including the highest mountain on the Iberian Peninsula, Mulhacén, at 3,842 metres – as well lying above the conversion of several faults.
Activity on one fault triggers seismic activity on adjacent faults, the result is what seismologists call a seismic swarm.
Scientists have also discovered that the Sierra Nevada has been gradually rising for millions of years. In the last 8 million years, some areas have risen at least 2,000 metres. And this process is still ongoing, at a rate of around one millimetre per year.
This process creates tension over a long period of time and when it’s released, it comes out in the form of an earthquake or tremor and the mountains grow ever so slightly.
Nieves Sánchez Guitián, president of the Official College of Geologists explains: “A fault doesn’t necessarily release all its energy at once, but rather, in this case it’s clear that it’s the same site, the same fault, the same geological area”.
Scientists know all this because they have found marine sediments in the Sierra Nevada which were deposited there around 8 million years ago, meaning the area was once at sea level.
READ ALSO: What are the chances of a major earthquake happening in Spain?
Shallow quakes and sediment
A further reason why earthquakes have been felt so much in Granada is because they’re very shallow compared to many quakes.
Spain’s National Geographic Institute (IGN) has confirmed that the 348 events recorded since August 14th have all occurred less than 10 kilometres below the surface.
The shallower they are, the more intensely they’re felt on the surface.
Again this is likely due to the amount of sedimentary material within the Granada Basin, making the ground less solid than in very rocky areas.
