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Antonio Aretxabala Díez, , Geologist. Professor of the School of Architecture of the University of Navarra.
Chronicle of a seismicity foretold
Last March 22 was celebrated the international day of water, never better chosen date, nor wanting to have been done better, the head of climatology area of the AEMET, Antonio Mestre, explained that March will also be historic, until March 25, already exceeded twice the normal value for this period. In fact, he added that in some areas of Andalusia as Jaén or east peninsular, as well as in Navarra, areas currently immersed in crisis has fallen between four and five times more than normal. Not even the historical 1947 exceeds it.
Especially Navarra and Jaén have made history. On July 20, 2011, the scientist of the high school of Geosciences of Madrid of the CSIC Miguel de las Doblas suggested a novel hydroseismic model according to which the overexploitation of the Lorca aquifer could have decisively influenced the genesis of the Lorca earthquake that devastated the city on May 11 of the same year.
After the floods that devastated the Guadalentín valley at the end of September 2012 in the vicinity of Lorca, Miguel de las Doblas suggested in November 2012 that there could be a "rebound" effect in the overexploited aquifer that would be filled again abruptly and that could again affect the seismicity along the Alhama de Murcia fault. A headline read: "A scientist assures that the rains could provoke another earthquake: The researcher of the CSIC Miguel Doblas says that when the aquifer swells due to the flood, new tension is added to the fault".
In the report it is added that "The CSIC scientist has dared to assure that the recent floods in this area of Murcia could lead to a new earthquake in a short time deadline , because the "swelling" of the aquifer adds new tension to the fault", several newspapers repeated the news. No specialist gave credibility to this suggestion. Since a few weeks ago, and especially yesterday, seismic activity along the Alhama de Murcia fault in the vicinity of Lorca seems to have suddenly reactivated and it seems that the prediction made in November last year is coming true.
Hydroseismicity: an undeniable reality
Since Costain and other authors coined this concept in 1987, which highlights the cause-effect relationships between climate, rainfall (water) and shallow magnitude earthquakes, it has been demonstrated in the scientific bibliography worldwide that rainfall is capable of triggering seismic events: results from more than 30 programs of study conducted worldwide during the last quarter century, on all five continents, demonstrate that hydroseismicity is a viable hypothesis to explain interplate seismicity.
Water level rise in aquifers and fluid pressure diffusion, independent of the tectonic regime, is capable of triggering faults. It can no longer be assumed that variations in the level of deep aquifers have no impact on the seismic risk of an area. The evidence that climate has an influence on tectonic movements is increasing at each specialized congress : water from rain, rivers, lakes, or seas seeps through any fissure it finds in the porous crust, including fractures or faults.
In cortical sectors with the right combinations of connected/permeable fractures and groundwater, natural water surges in water recharge zones can be transmitted to depths of up to 10-20 km and produce earthquakes. The idea that climate change and seasonal variations in climate can influence earthquakes is by no means an eccentric hypothesis.
Although we all know that the power of seismicity comes from the movements of the plates at great depths, even these massive Structures can be influenced by what happens at the surface that can slow down or increase the occurrence of earthquakes. In addition, any element that increases or decreases the weight supported by the crust generates deformations and stresses. When this occurs above one of the many existing faults where the crust is already "prestressed", it can increase or decrease its potential for seismic slip. There is one very heavy substance whose movements are highly dependent on climatic conditions: water (Mcguire, 2012).
This time the politicians are ahead of the game
After what happened in Italy with the unjustified condemnation of scientists who did not know how to prevent the L'Aquila earthquake, we believe that a hypothesis such as that of hydroseismicity must be taken into account because it has the enormous advantage of being able to provide obvious preventive measures to mitigate the future recurrence of at least one subject of seismicity; it can also suggest a strict control of human activities to prevent them from causing the level of aquifers to vary abruptly: controlling uncontrolled abstractions or the filling of reservoirs.
In addition, and according to foreign scholars, the model hydroseismic has the potential to predict the recurrence of earthquakes in areas where its viability is proven, since in principle, after a massive water recharge in a river basin, an increase in seismicity can be anticipated (see the case of Lorca or Jaén). It is curious that the areas pointed out by Antonio Mestre today suffer from hydro? seismicity, the issue has already reached our leaders, it seems that finally, in some obvious issues politicians are ahead of scientists, the former have already realized.
Navarra has already won a first battle in the recognition of this hypothesis, when the region of Navarra is shaking because of the historic rains of a winter that has no equal in historical records, even the IGN has officially accepted the influence of water to explain part of the recent seismic series around Pamplona, it is possible that it was the Etxauri fault that generated the earthquake early last Saturday morning, its hydroseismicity is still waiting to be recognized and will do so, among other things keeps in its head a huge collapse by dissolution.
In Jaén, the more than 2000 earthquakes that have been suffering in the hill of Úbeda since October 2012 have also been explained by Miguel de las Doblas and the undersigned, the devastating effect of the recent and massive rainfall refilled the deep aquifers of the area after a drought and historical extractions, they had even been illegally exploited since 1995, not only for the intensive cultivation of olive groves which was their initial purpose; Green gardens with swimming pools could be seen in August, geraniums that would not envy those of Santillana del Mar grew with groundwater.
However, the hydroseismicity assumed by a large part of the population of Jaén is still not accepted institutionally, perhaps due to the numerous sectorial interests created, despite the fact that this hypothesis for Jaén has already been accepted by the most important geophysical organization in the world ("American Geophysical Union"), and that the inhabitants of this region can directly verify the infallible temporal correlations between an intense episode of rainfall and the recurrence of seismicity.
Something similar happens in Lorca where the hydro-seismic hypothesis of Miguel de las Doblas (corroborated a year later in Nature Geosciences by Avouac, 2012; and González et al..., 2012) does not obtain the slightest approval from researchers or local authorities, who remain determined to deny the obvious: the overexploitation of the Guadalentín aquifer and the subsequent rains have undeniable effects on the destabilization of the Alhama de Murcia fault that was already "pre-stressed" and therefore the water factor constitutes "the straw that breaks the camel's back", today we can almost say: we are facing one of the longings of human beings, to anticipate, even if for the moment only to a very specific subject , seismicity. It seems that in this country with so few resources at research, there is still some gray substance and room for scientific success.