Identified a parameter able to monitor in a simple and fast way the evolution of the state of the Phlegrean Caldera over time. This was highlighted by a team of INGV researchers. The study was published in Scientific Reports (Nature)
Predicting the evolution of a volcano's activity requires the joint interpretation of seismicity, ground deformations and variations affecting the emitted fluids (composition of fumaroles, total flows, etc.). A group of researchers from the National Institute of Geophysics and Volcanology (INGV - Bologna section and Vesuvius Observatory, Naples), University of Granada (Spain), University of Aberdeen (UK) and CNRS (France), has identified a parameter, defined by the authors background seismicity, able to monitor, in a simple and fast way, the evolution over time of the state of the Campi Flegrei caldera. The study Clues on the origin of post-2000 earthquakes at Campi Flegrei caldera (Italy), has been published in Scientific Reports (Nature) - https://www.nature.com/articles/s41598-017-04845-9
"The interpretation of all the signals associated with these phenomena is particularly complex in the case of calderas," says Giovanni Chiodini, INGV researcher and first author of the article. “Sometimes, the succession of earthquakes associated with strong elevations of the ground and the increase in the vapors emitted by the volcano does not always anticipate an eruption. The opposite can also happen, i.e. that eruptions are preceded only by weak variations in geophysical and geochemical signals".
The relationship between hundreds of micro-earthquakes, which occurred in Campi Flegrei after 2000, with ground elevation and variations in the composition of the fumarolic vapors of the Solfatara, was investigated by researchers with a statistical approach.
"The seismological observable under examination was obtained by eliminating all the events that constituted an earthquake swarm from the recorded seismicity catalog (in practice, each swarm was considered as a single event), assuming that the physical process linked to the occurrence of the latter had a different genesis”, continues Chiodini.
The sum of the time series of the earthquakes thus selected, defined as background seismicity, shows a behavior very similar to the pattern of ground elevation and to that of the increase in concentration in the fumaroles of the gaseous species most sensitive to temperature.
In particular, "starting from 2008, the curves representing background seismicity and ground uplift are practically coincident", adds the INGV researcher. “The background seismicity, ground uplift and concentration increase in temperature-sensitive fumarolic species also show a time trend very similar to the simulated temperature increase in a virtual system subjected to repeated injections of very hot fluids ( of magmatic origin in our interpretation)”
Although seismicity, ground deformations and geochemical variations are measured with clearly independent methods, they show at Campi Flegrei, during the bradyseismic phenomenon, an absolutely coincident temporal pattern.
“The three phenomena would therefore refer to a single process that controls the current phase of unrest (attention) in the area. The direct consequence of these observations is that background seismicity, a simpler parameter to monitor than ground deformations and geochemical variations (which need complex processing and greater time commitment), could be an excellent estimator of the evolution in the time of the state of the Phlegraean Caldera. Obviously the background seismicity would be an additional parameter and not a substitute for the other parameters. Any deviation that could be detected with respect to the current correlations could be indicative that something has changed in the process that causes the volcano to unrest”, concludes Chiodini.
The research carried out has an essentially scientific value, with no immediate implications regarding the aspects of civil protection at the moment. It should be remembered that since December 2012 the Campi Flegrei, which are continuously monitored and studied by INGV, have been at the "yellow" alert level (attention).
Abstract
The inter-arrival times of the post-2000 seismicity at Campi Flegrei caldera are statistically distributed into different populations. The low inter-arrival times population represents swarm events, while the high inter-arrival times population marks background seismicity. Here, we show that the background seismicity is increasing at the same rate of (1) the ground uplift and (2) the concentration of the fumarolic gas species more sensitive to temperature. The seismic temporal increase is strongly correlated with the results of recent simulations, modeling injection of magmatic fluids in the Campi Flegrei hydrothermal system. These concurrent variations point to a unique process of temperature-pressure increase of the hydrothermal system controlling geophysical and geochemical signals at the caldera. Our results thus show that the occurrence of background seismicity is an excellent parameter to monitor the current unrest of the caldera.
Photo 1 - Overview of the Monitoring Room of the Vesuvius Observatory, Naples Section of INGV
Photo 2 - Intense degassing activity at the Pisciarelli fumarole, area east of the Solfatara