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Antonio Aretxabala Díez, , Geologist. Professor of the School of Architecture of the University of Navarra.

Our earthquakes and our cultural heritage

Fri, 29 Mar 2013 13:25:00 +0000 Published in News Journal


The citizenship participates in the scientific and cultural discussion , in this lies the Navarrese treasure of social health. Yesterday, in the Planetarium of Pamplona, we witnessed a high level of social awareness that surprises for its high Degree of knowledge. Physicists, engineers, architects, geologists, biologists, students, workers of the former Potasas, citizens of Etxauri, of El Perdón.... A whole exchange of observations, ideas and brilliant proposals about the latest seismic events. Wisdom is in the street. The flow of information is changing, the university is no longer the only source, the unidirectionality of the movement of knowledge no longer flows only from it. Social networks educate, disseminate, everything works if you know how to use them.

One thing became very clear: nature in Navarre is one of our greatest treasures, and people love it very much, a treasure that both gives us and takes away from us, we act on our territory and talk about it as if we were its owners. Nature, also in Navarre, is already a social issue because we have made it social, when we say our natural heritage we express a profoundly modern attitude, it is true, but also one of arrogance and appropriation of a dynamic that we hardly understand and even less can control. The equation about the origin of the earthquakes that still spring up around Pamplona was one of the most commented points. The data provided by the people who lived in first person the withdrawal of the Potasas galleries and the subsequent evolution of the current seismicity, decades after those events, coincide with the data provided by the IGN. Now then, to concatenate facts that already seem clear is not only risky, but also brave, but at the same time revealing. The Earth always puts us back in our place. The Navarrese society had assumed that these galleries would close and compact, that everything would return to its original state, something unimportant for future generations, but...

The historic rains of this winter and spring, without known precedents, penetrated deep into the Sierra del Perdón, caused the dissolution of salts and the collapse of cavities and galleries that channeled the access of clean water from rain and snow to hitherto inaccessible areas; thus, so much movement, rumbling and vibration, accompanied by a tremendous rise in water levels, also trapped air that was compressed and literally exploded like a balloon.

The faults in the area, in deep zones were stimulated, their reaction showing epicenters at 2, 3 and up to 4 kms. deep already indicated that it was not the galleries that were collapsing, but something more important, so it was encouraged by a phenomenon of stress transfer to these faults greased with so much water and subjected to fluid pressure to shoot, in turn these to the adjacent ones and these to others, and that is how the seismic swarm began.

This phenomenon, through its own connections and resources, was also able to stimulate through the Belascoáin corridor faults that were already in the main trace of the most famous tectonic feature of the Basin: the Pamplona fault and its other associated faults such as the Etxauri fault. It is possible that it was precisely this fault that also pre-stressed, and already lubricated and stimulated, triggered early Saturday morning (4.2 ML), but its activity was already announced days before with premonitory and even more energetic earthquakes, such as the one on Thursday, March 21 in Ciriza (3.8 ML); the aftershocks in both areas are still going on. The hypocenter remains to be clarified, there are data between 5 and 40 kms.

Yesterday, the most awakened citizens wondered at the Planetarium, with all the honesty and brilliance that unprejudiced minds can grant to the scientific or observant human being, about the origin of this domino effect: where did it begin? Did it begin on February 14 because of the enormous rains, or did it begin in the eighties when dozens of kilometers of water channels entrance were abandoned to their fate towards the Keuper salts under the Perdón mountain range, who expected more than 600 liters in three months?

We have taken measures to construct our buildings from the development of seismic-resistant standards, but these have not been, are not and will never be enough, we have not taken precautions in intra-plate environments as we have done on the edges of them. The seismicity of Navarra, and especially that of the Pamplona basin, has its own personality, and as we get to know it, we see that it bears little resemblance to that of Granada or Lorca.

Pamplona, on March 10, 1903, was nothing more and nothing less than three hours suffering impacts, this comes to light when it thunders, we all remember then Santa Barbara. We have to think about it as soon as possible and plan accordingly. We can no longer assume that no damage will result from the reduction and changes in the water table like the one we are experiencing, it will not be the last hydroseismic episode we will experience.

I hope that with time governments will recognize that anthropogenic damage can become a reality; and worse if we continue to avoid contributing funds from research that we should dedicate to the understanding of this fragile interface, between the atmosphere and the hydrosphere, in which we live. We have taken possession of it, we have turned it into a natural heritage because we are so modern, but we hardly know it, we do not even know how it reacts, and even less how we can control it.