Tidal and hydrological periodicities of seismicity reveal new risk scenarios at Campi Flegrei caldera

Simona Petrosino,Paola Cusano,Paolo Madonia

doi:10.1038/s41598-018-31760-4

Simona Petrosino, Paola Cusano + Show 1 more

Open Access

https://doi.org/10.1038/s41598-018-31760-4

Copy DOI

Abstract

The volcano-tectonic seismicity occurring at Campi Flegrei caldera during its present unrest phase, started in 2005, is distributed into time-clustered events emerging from a background composed of earthquakes with higher inter-arrival times. Here, we show that clustered seismicity is cyclically recurrent at time scales from semidiurnal to annual, matching tidal and hydrological periodicities. These results suggest that volcano-tectonic seismicity at Campi Flegrei caldera is driven by both variations in the deep magmatic feeding system and exogenous phenomena, as rainfall or global inflation/deflation cycles of the Earth’s crust, controlled by the lunisolar interaction. Consequently, the role of exogenous triggers in the evolution of the present unrest phase should be properly considered in the elaboration of volcanic risk scenarios, presently limited to the study of surface indicators of deep phenomena.

Highlights

External forcing of seismic and volcano-seismic activity by hydromechanical coupling of instable, shallow fault and hydro-magmatic systems with infiltrating rainwater has been documented in various geological settings[1,2], as well as synchronization between tides and hydrothermal seismicity[3,4,5,6]
The Campi Flegrei caldera (CFc) uplift episodes have been accompanied by VT seismicity often occurring in swarms; these earthquakes generally concentrates in few hours or even minutes and they are usually located beneath the Solfatara-Pozzuoli area, at depth up to 4 km[14,15] (Fig. 1)
After performing an inter-event time (IET) analysis on the 2005–2016 CFc seismicity, we found a bi-modal distribution which corresponds to two ensembles divided by a time-interval of about 1 day

Summary

Introduction

External forcing of seismic and volcano-seismic activity by hydromechanical coupling of instable, shallow fault and hydro-magmatic systems with infiltrating rainwater has been documented in various geological settings[1,2], as well as synchronization between tides and hydrothermal seismicity[3,4,5,6]. The possible effects of exogenous processes in the evolution of a restless volcano from unrest to eruptive conditions do not commonly deserve the necessary attention, which is instead focused on the interpretation of the surficial manifestations of deep processes This approach could be critical when dealing with restless calderas, whose eruptions can be preceded only by small unrest signals[7,8]. A strongly accelerating ground uplift rate was recorded between April 2012 and January 2013, inducing the Italian Civil Protection to raise the volcanic alert level from “background” to “attention”[12] This episode was accompanied by an anomalous seismic swarm, occurred on September 7th 2012 and lasted about 1.5 hours, consisting of about 200 earthquakes with hypocentres located outside the area normally affected by seismicity (Fig. 1) and very close to the northern edge of the inferred inflating magmatic reservoir[12]. A good correlation among ground deformation, seismicity and geochemical characters of surface hydrothermal degassing was found, and it was interpreted as the effect of recurrent injections of magmatic fluids into the 2 km-deep hydrothermal reservoir[10,12,13]

Methods

Results

Conclusion