A new study, the result of collaboration between Sapienza, Ingv and Cnr, has found some variations in the level of groundwater in central Italy, attributable to distant earthquakes, which even occurred on other continents.
The "hunt" for the seismic precursor continues, this time with one more element. As already documented in recent years in numerous studies, there is an association between the triggering of earthquakes and variations in the circulation of groundwater. What is not yet adequately known is how this phenomenon also affects teleseisms, distant earthquakes that have occurred on other continents, the effects of which are felt thousands of kilometers from the epicenter.
Shedding light on the unexpected relationship between seismicity and groundwater is a new study, the result of a collaboration between the Sapienza Department of Earth Sciences, the National Institute of Geophysics and Volcanology and the National Research Council. The results, published in the journal Scientific Reports, represent a further step towards a possible future identification of seismic precursors in waters.
For five years, the researchers monitored the level of an aquifer in Popoli, in Abruzzo, where they observed, in addition to the signs left by seismic events that occurred in the immediate vicinity, anomalous behavior of the water, the triggering engine of which was on the other side of the Earth: 18 strong oscillations have been identified as an "impulsive" response of groundwater to earthquakes of magnitude greater than 6.5 that occurred all over the world, even more than 18.000 kilometers away from the observation site.
"From the hydrogeological and seismic investigation it emerged that the seismic waves responsible for the perturbations are the Rayleigh waves which travel on the earth's surface, reaching enormous distances – explains Carlo Doglioni of Sapienza and president of Ingv. Now that we have identified the perturbations caused by distant earthquakes, we have one more tool to distinguish them from the precursory signals induced by nearby earthquakes".
The study also attests to a correlation between the distance of the earthquake and its magnitude with the extent of the oscillation of the water table: evidence that confirms the importance of these factors in controlling the behavior of groundwater in a given site, and not Alone. “The nature of the aquifers – explains Marco Petitta of the Sapienza Department of Earth Sciences – certainly plays a fundamental role in the response of water to seismic activity. Contrary to what happens for porous aquifers, intensely fractured carbonate aquifers, such as the one we monitored in Abruzzo, are much more sensitive to deformation events. Precisely this aspect becomes essential in identifying a water-sensitive site to seismicity".
The phenomenon, also recently highlighted by a similar study conducted in China, still remains a subject of in-depth study by the research team. Meanwhile, the results of the study open up new ways on the criteria to be taken into account in choosing the site to be monitored and represent a guide in the field of hydrogeological monitoring applied for seismic purposes.
