A document by Simone Masoch. Click on the document to view its contents.

In active volcanic systems, the elevated pressurization of fluids and the movement of melt materials have an enormous influence on the stress-state of rocks and their mechanical behavior. We use seismic ambient noise to evaluate the static seismic velocity variations related to long-term volcanic deformation, and the dynamic changes associated with the 2017 Casamicciola earthquake (Mw 3.9), in the active volcanic complex of the Ischia Island (Italy). Our study reveals a significant dynamic velocity reduction mostly related to the near-surface damage, with a permanent drop near the red zone, that we posit to be related to the documented landslides and the subsidence observed immediately after the earthquake. We also report a positive long-term linear trend of velocity variations, sensitive to a generalized contraction of the Ischia Caldera that we revealed with geodetic modeling. Our results suggest a depressurization of the shallow hydrothermal system, through degassing along faults or sills.

Continuous seismic data analysis identifies signals related to physical processes within the Earth or on its surface. Characterizing seismic signals yields insights into source processes and Earth’s structural features. Global seismic network analysis of long-period (25–100 s) surface waves has detected seismic events not identified through high-frequency body wave analysis. However, detecting long-lasting monochromatic signals with narrow spectral peaks, which carry valuable information about geological and environmental processes, remains challenging on a global scale. We developed a coherence-based method to characterize long-period monochromatic signals on a global scale. In addition to signals originating from the Gulf of Guinea, Vanuatu islands, and a submarine volcano, we observed a previously unidentified signal originating from the Canadian Arctic, likely associated with glacier dynamics. Our approach explores long-period monochromatic seismic signals in continuous seismic data, providing a foundation for future studies to characterize the physical processes generating these signals on Earth’s surface.