Strange but not unprecedented. The earthquake recorded early Monday morning in Alava, with its epicenter in the town of Iruña de Oka, was in fact the largest magnitude (4) recorded so far in the Basque Country, as confirmed 20 minutes Luis Cabañas, seismologist at the National Geographic Institute (IGN).
However, this expert indicates that there is evidence that two earthquakes of intensity 5 occurred in Alava in the years 1916 and 1929, classified by their effects on the buildings and the people who felt them, given that their magnitude could not be recorded due to the lack of seismic observatories in the area at that time. They performed in the Alava villages of Villavezana and Salvatierrarespectively.
This Monday morning, the ground in Alava shook again and noticeably at 12:10 a.m. Those who felt it spoke of “two very strong blows, like explosions.” Without causing damage or injuries, this earth movement was also noted in the capital, Vitoria-Gasteiz, as well as in the cities of Burgos or La Rioja.
Review of the IGN archives, The previous largest earthquake recorded in the Basque Country dates back to 1965: 3.8 and its epicenter was in Azilu, a council of the Alava municipality of Iruraiz-Gauna.
María Belén Benito, professor at the Polytechnic University of Madrid and expert in seismic risks and risks, consulted on the recent seismic activity, highlights the fact that A few hours before the earthquake in Iruña de Oka (Alava), another earthquake occurred in Fuengirola (Málaga) with a magnitude of 4.9. The latter, due to its great depth (75 kilometers), was less felt and less alarming, he indicates: “And that of Fuengirola was 30 times greater (each degree of magnitude multiplies the energy by 30) than that of Iruña de Oka. However, this one, of magnitude 4 but of shallow depth, meant a lot of unrest among the population“.
For IGN seismologist Luis Cabañas, what happened in Iruña de Oka, in Alava, is “surprising and unusual”, but he warns that “a magnitude 4 earthquake can occur anywhere on the peninsula because we have a fractured crust in which tensions accumulate.” And he adds that even if “history shows us areas where they are more frequent, nothing can be excluded.”
Professor María Belén Benito of the UPM agrees on the seismic potential of the entire peninsula. “The earth’s crust is sufficiently fractured that produce earthquakes of magnitude 4 or even 5 at any point. And in Andalusia more, between 6 and 7″.
Benito explains that the magnitude of an earthquake depends on the length of the surface of the tectonic faults and that the greatest seismic risk has been located in the Betic faults, in Andalusia, where earthquakes of magnitude 6.8 have recently occurred. The last, the most destructive, took place in 1834 in Granada and left a thousand dead. It was classified as intensity of 9 to be very destructive since at that time there were no instruments to measure size.”
Correlation between northern and southern earthquakes
In Spain Earthquakes tend to occur with greater frequency and magnitude in Andalusia, but also in the Levante, Murcia or Alicante, as well as in the Alboran Sea.. In fact, this Monday an earthquake of 2.6 was recorded in Murcia and this Tuesday two other earthquakes of magnitude 3.7 were recorded almost in a row in the Alboran Sea, in Melilla.
Regarding this rate of earthquakes in recent hours, both in the north and south of the peninsula, experts explain that It is “difficult” to establish a direct connection, because the epicenters are sufficiently distant to rule out the possibility that one could have fired on the others.
“The correlation between distant earthquakes is something that needs to be studied slowly. These are moderate, small earthquakes. It is difficult to establish the cause and effect link. Seismic movements are unpredictable and have no periodicity, even if some can trigger or accelerate other faults, I tend to think that it is pure chance”, estimates Cabañas, seismologist from IGN.
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