Fluid migrations and volcanic earthquakes from depolarized ambient noise

S Petrosino,L De Siena

doi:10.1038/s41467-021-26954-w

S Petrosino, L De Siena

Open Access

https://doi.org/10.1038/s41467-021-26954-w

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Abstract

Ambient noise polarizes inside fault zones, yet the spatial and temporal resolution of polarized noise on gas-bearing fluids migrating through stressed volcanic systems is unknown. Here we show that high polarization marks a transfer structure connecting the deforming centre of the caldera to open hydrothermal vents and extensional caldera-bounding faults during periods of low seismic release at Campi Flegrei caldera (Southern Italy). Fluids pressurize the Campi Flegrei hydrothermal system, migrate, and increase stress before earthquakes. The loss of polarization (depolarization) of the transfer and extensional structures maps pressurized fluids, detecting fluid migrations after seismic sequences. After recent intense seismicity (December 2019-April 2020), the transfer structure appears sealed while fluids stored in the east caldera have moved further east. Our findings show that depolarized noise has the potential to monitor fluid migrations and earthquakes at stressed volcanoes quasi-instantaneously and with minimum processing.

Highlights

Ambient noise polarizes inside fault zones, yet the spatial and temporal resolution of polarized noise on gas-bearing fluids migrating through stressed volcanic systems is unknown
Our results show that polarized noise detects both the extensional faults and the transfer structure at the caldera during periods of low seismic release
The depolarization of the transfer structure marks both injections at the start of seismic unrest and lateral fluid migrations leading to earthquakes

Summary

Introduction

Ambient noise polarizes inside fault zones, yet the spatial and temporal resolution of polarized noise on gas-bearing fluids migrating through stressed volcanic systems is unknown. We show that high polarization marks a transfer structure connecting the deforming centre of the caldera to open hydrothermal vents and extensional caldera-bounding faults during periods of low seismic release at Campi Flegrei caldera (Southern Italy). Numerical modelling[22], and deformation inversions[27] infer the existence of NE-SW-trending transfer structure, feeding volcanic activity connecting primary deformation source and degassing vents[28,29] Both extensional faults and transfer structure were likely crucial for developing volcanic unrests monitored during the last thirty-six years. Our results show that polarized noise detects both the extensional faults and the transfer structure at the caldera during periods of low seismic release. The results detect structures and processes leading to hazard at Campi Flegrei caldera, offering a new technique to monitor fluid-derived processes across highly-stressed volcanoes in real time

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