For months the seismic activity in the Flegrei fields shows no sign of stopping; As well as bradisism, that is, the raising (or lowering) of the soil that characterizes volcanic activity in the caldera. The causes of the two phenomena are obviously attributable to the supervulcan on which the area stands, but the specific mechanisms that determine the intensity and frequency of earthquakes and the movements of the soil are still to be discovered. Knowing them better the seismic dynamics would help to foresee the dangers that residents run greater forecast, and indicate potential strategies to reduce risks. This is the direction in which two new searches go, published on AGU Advances and on Science Advances.
A weak layer in the earth’s crust
The first of the two studies was born from a collaboration between the National Institute of Geophysics and Volcanology (Ingv), the University of Grenoble Alpes and the University of Bologna. And it was made thanks to an in-depth analysis of rocky samples extracted from a geothermal well about 3 kilometers deep, located towards the center of the Caldera, integrated with the study of high-resolution three-dimensional images of the subsoil and models that allowed to simulate the ascent of the magma with a deep tank, placed about 7-8 kilometers of depth.
“We have identified an important transition to about 2.5–2.7 km of depth, where a weakening of the crustal layers is observed. Below this threshold, the crust appears more porous and permeable than expected, and therefore less resistant, favoring the accumulation of magmatic fluids”, explains Lucia Pappalardo, ingv and co -author of the study. “These fluids, trapped, gradually increase in volume and pressure, triggering soil deformations and seismic activity”.
The simulations made by the researchers have shown that in the past on several occasions, small magma intrusions have reached this transition area between deep carbonate rocks and superficial volcanic tuffs, causing its progressive weakening. “This research does not directly affect our short-term forecasts, but it is a fundamental piece to understand the behavior of the volcano and improve our ability to monitor it”, underlines Mauro Antonio di Vito, director of the Vesuvian Observatory (Ingv-Ov). “Only with an increasingly detailed knowledge of the volcanic system and its dynamic can we hope to anticipate critical signals and reduce the risks for people”.
Like a mocha, under Naples
Of different sign, however, the results of another research published in these days on Science Advances From a team of Stanford researchers led by Geophysics Tiziana Vanorio. The study, carried out by analyzing images obtained with the tomography, a sort of tac of the subsoil, and on laboratory analysis carried out on rocks of rocks taken in the caldera, has compared the bradisismic crisis of 1982-84 with the one in progress since 2022, demonstrating a common origin that differs from the most accredited ones, which bind the seismicity to the resalpice of magma and gas Volcanici.
According to their results, the culprit should be sought rather in a geothermal sand tank and porous rocks placed about 2-4 kilometers of depth, which slowly fills with water that filters from the rainfall on the ground above. Once full, the water of the tank would overheat as a result of the underlying magmatic chamber, and finding itself stopped by a layer of waterproof rock would generate strong pressure, thus causing earthquakes and raising the above soil. Results confirmed also during a series of laboratory experiments.
If the conclusions of the researchers are correct, therefore, the magma would not be the direct cause of the problems experienced in recent years in the Flegrei fields, but rather the water accumulated in the geothermal tank above. And this would offer the possibility of intervening to reduce the pressure, and thus prevent earthquakes and land deformations. “To solve the problem you could intervene on the water on the surface, or perhaps reduce the pressure by emptying the wells of the region from the water,” explains Vanorio.
In the city sleeping on the volcano at risk of collapse one in ten house