Abstract
Volcanoes are complex systems whose dynamics is the result of the interplay between endogenous and exogenous processes. External forcing on volcanic activity by seasonal hydrological variations can influence the evolution of a volcanic system; yet the underlying mechanisms remain poorly understood. In the present study, we analyse ground tilt, seismicity rates and rainfall amount recorded over 6 years (2015–2021) at Vesuvius and Campi Flegrei, two volcanic areas located in the south of Italy. The results indicate that at both volcanoes the ground deformation reflects the seasonality of the hydrological cycles, whereas seismicity shows a seasonal pattern only at Campi Flegrei. A correlation analysis on shorter time scales (days) indicates that at Vesuvius rain and ground tilt are poorly correlated, whereas rain and earthquakes are almost uncorrelated. Instead, at Campi Flegrei precipitations can affect not only ground deformation but also earthquake rate, through the combined action of water loading and diffusion processes in a fractured medium, likely fostered by the interaction with the shallow hydrothermal fluids. Our observations indicate a different behavior between the two volcanic systems: at Vesuvius, rain-induced hydrological variations poorly affect the normal background activity. On the contrary, such variations play a role in modulating the dynamics of those metastable volcanoes with significant hydrothermal system experiencing unrest, like Campi Flegrei.
Highlights
In the recent years an increasing number of observations has been showing how rainfall-induced stress variations play a role in modulating ground deformation and seismic activity
In the present paper we investigate and compare the possible links among rainfall, ground deformation and seismicity at two of volcanoes currently characterized by different activity: Vesuvius, which is in a quiescent state, and Campi Flegrei, a caldera experiencing unrest
The results indicate that, at both Vesuvius and Campi Flegrei ground deformation is sensitive to the input of meteoric water, the two volcanic systems respond in a different way to rain-induced hydrological variations
Summary
In the recent years an increasing number of observations has been showing how rainfall-induced stress variations play a role in modulating ground deformation and seismic activity. At Vesuvius a correlation between rainfall and seismicity has not yet been observed; modulation of seismic activity on short (daily) time scales has been interpreted to be linked to a number of possible mechanisms related with the cooling/warming diurnal cycle of the volcanic edifice and/or with the daily oscillation of the geomagnetic field (Mazzarella and Scafetta, 2016). At a stressed caldera like Campi Flegrei the rainfall can modulate ground deformation on different time scales and earthquake rate. These observations suggest that the Campi Flegrei dynamics is the result of a complex interplay between endogenous and exogenous processes. It is important to remark that correlation tests a relationship between two variables, but it does not imply causation
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