A new study analyzes the slow ground uplift of Campi Flegrei and the seismic activity that accompanies it, to measure its rapidity and understand its evolution
In the period 2000-2020, through the data acquired by the Global Positioning System (GPS) and by the seismic network, two superimposed trends of ground uplift and seismicity in the Campi Flegrei area were recognized and measured: an acceleration on a ten-year scale and periodic swings.
These are the results of the study "Data analysis of the unsteadily accelerating GPS and seismic records at Campi Flegrei caldera from 2000 to 2020”, recently published in the journal 'Scientific Reports' of Nature conducted by a team of researchers from the National Institute of Geophysics and Volcanology (INGV), the Scuola Normale Superiore of Pisa and the Universities of Buffalo, Tufts and Penn State (USA).
Since the 50s, the Campi Flegrei caldera has been affected by significant ground movements, including the slow uplift that has been going on for almost twenty years. This phenomenon is called bradyseism and is characterized by a sequence of deformation episodes accompanied by increases in seismic activity.
The objective of the study was to understand the rapidity of the bradyseismic phenomenon and its possible evolution. Furthermore, the scientists investigated the presence of periodicity phenomena in the episodes of ground deformation and the most intense seismicity.
To this end, the researchers mathematically analyzed the speed and acceleration of the caldera ground uplift, the number of seismic events and their cumulative energy also comparing the data recorded in the period 1983-2000 with those recorded in the period 2000-2020. This analysis allowed the recognition of two superimposed temporal trends: an acceleration on a ten-year scale and recurring oscillations of various frequencies.
"Our analyses", explains Flora Giudicepietro, researcher at the INGV Vesuvius Observatory and co-author of the study, "show an increase in the velocity of ground uplift and an increase in the frequency of occurrence of earthquakes since 2005. 90-97% of their increase was recorded after 2011 and 40-80% after 2018. soil is still continuing and in October 2022 at the Rione Terra di Pozzuoli station the vertical displacement compared to the values recorded in 2005 reached about 100 cm, as reported in the Bulletins periodically issued by the Vesuvius Observatory".
A further result of the study concerned the recurrence times of the periodic oscillations of the signals.
“The recorded velocities exhibit consistent swings between uplift signals and the number of seismic events”, explains Andrea Bevilacqua, researcher of the Pisa Section of INGV and first author of the study. “We have observed seven major swings since 2000, one about every 2,8 to 3,5 years, with minor swings at about halfway between these intervals. From the signals, a longer period cycle has also been identified, equal to 6,5-9 years”.
The detailed study of acceleration on a ten-year scale has also allowed further estimates.
“In order to estimate the acceleration properties on a decadal scale, we applied a representative model of the dynamics leading to failure in brittle elastic materials subjected to constant stress”, continues Andrea Bevilacqua. “This allowed us to calculate theoretical limit times for this acceleration, potentially representative of a critical state of the system, in the order of 10 or 20 years depending on whether we consider the seismic activity data or the ground deformation respectively . It is important to underline that the model is valid in the hypothesis that the trends observed in the last two decades continue in the same way in the future”.
"The estimate of the ten-year acceleration recorded since 2005", concludes Augusto Neri, INGV researcher and co-author of the study. "is a particularly relevant aspect that emerged from the analysis. It should be clarified that the estimated time limits do not correspond to absolute probabilities of the occurrence of eruptive events due to the simplified nature of the model adopted and, above all, because the ten-year acceleration observed so far in the data could change in the future, both slowing down and accelerating more . However, the results of the study represent a further stimulus to keep our guard up on the future evolution of the Flegrea caldera".
The published research has an essentially scientific value, without immediate implications regarding the aspects of civil protection at the moment.
Link: https://www.nature.com/articles/s41598-022-23628-5
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Fig 1 - GPS monitoring network of Campi Flegrei.
Fig. 2- (a) Overview of ground uplift recorded at the center of the Campi Flegrei caldera from 1983 to 2020. Data combine leveling (landmark 25A) and GPS data (RITE station in Rione Terra). (b) Overview of the earthquakes recorded in Campi Flegrei from 1983 to 2020. In both figures, the data recorded from 2000 to 2020 analyzed in the study are highlighted in blue (from the INGV periodic Bulletins for Campi Flegrei http://www.ov.ingv.it).
Fig. 3 - Synoptic panel comparing (a,c) the count of seismic events and (b,d) the displacement of the ground from 2000 to 2020. In the plots (a,c) the results concerning all the earthquakes in the catalog are in orange, and those that exclude swarms are in red. In plots (b,d) the ground uplift recorded at the RITE station is in red, and the horizontal displacement at the ACAE station is in blue. The plots (a,b) concern the cumulative data, while the (c,d) their speeds. In all plots the main peaks are highlighted with vertical black lines, dashed for the two less evident, while the secondary ones with dashed gray lines.