Tidal Modulation of Hydrothermal Tremor: Examples From Ischia and Campi Flegrei Volcanoes, Italy

Simona Petrosino,Stéphanie Dumont

doi:10.3389/feart.2021.775269

Abstract

Volcano dynamics results from an interplay between internal and external processes spanning different time scales. Unravelling how such processes interact may provide key insights into the mechanisms that may lead to the destabilization of the volcanoes and eruption, a critical information to forecast hazards. Studies dealing with tidal influence on volcanoes fall within this context, yet the cause-effect relationship between tides and eruptions is still poorly understood. In the present study, we investigate the tidal influence on two nearby volcanoes, Ischia and Campi Flegrei (Italy), characterized by intense hydrothermal activity. We analyze the seismic tremor of hydrothermal origin recorded by four seismic stations between January and June 2020 by using Singular Spectrum Analysis. We detect up to five long term tidal periodicities ranging from ∼5 to ∼29 days. The results indicate that the seismic tremor is modulated by Earth tides at both volcanoes. In addition, differences in phase and amplitude modulation between the response of both hydrothermal systems to tidal forcing reveal specific features related to the tremor source and to properties of the surrounding medium. These phenomena indicate an interplay between solid Earth and the dynamics of these two volcanoes. Similar approaches on hydrothermal systems at volcanoes would contribute to better characterize the hydrothermal circulation and their evolving conditions that may represent a precursor of a new phase of activity.

Highlights

IntroductionTidal influence has been evidenced at many volcanoes through the analysis of geological, geophysical, and geochemical time-series acquired during unrest and eruptive phases such as earthquake rates, frequency of explosive and/or eruptive events, volcanic tremor, gas, and lava fluxes (Dzurisin, 1980; McNutt and Beavan, 1987; Sottili et al, 2007; Sottili and Palladino, 2012; Girona et al, 2018; Dumont et al, 2020, 2021; Sahoo et al, 2021; Sottili et al, 2021)
The results indicate that the seismic tremor at both volcanoes is partly modulated by Earth tides; this modulation in phase and amplitude seems to vary with the nature of hydrothermal activity and underlying medium
We explore the tidal influence on hydrothermal activity at Ischia and Campi Flegrei using seismic tremor data and the Singular Spectrum Analysis (SSA) technique

Summary

Introduction

Tidal influence has been evidenced at many volcanoes through the analysis of geological, geophysical, and geochemical time-series acquired during unrest and eruptive phases such as earthquake rates, frequency of explosive and/or eruptive events, volcanic tremor, gas, and lava fluxes (Dzurisin, 1980; McNutt and Beavan, 1987; Sottili et al, 2007; Sottili and Palladino, 2012; Girona et al, 2018; Dumont et al, 2020, 2021; Sahoo et al, 2021; Sottili et al, 2021). By inducing a global mass reorganization on Earth on different time and space scales for both solid and fluid envelopes (Nakiboglu and Lambeck, 1980), solid Earth and ocean tides participate in changing the stress, strain, or pore-fluid pressure conditions that may be critical in dynamical systems such as volcanoes and faults (Jupp et al, 2004; Scholz et al, 2019; Dumont et al, 2022) This is illustrated by studies that have shown a correlation between the onset of volcanic eruptions and the lunar cycle for instance, e.g., Mauk and Johnston (1973); Dzurisin, (1980), or a sensitivity to Earth tides that appears with migration of magma towards the surface or when the systems get closer to a critical state (Berrino and Corrado, 1991; De Lauro et al, 2013; Girona et al, 2018; Miguelsanz et al, 2021). Such a response of volcanoes to tidal forcing has not been systematically reported, leaving many questions unsolved

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