Magma Degassing as a Source of Long‐Term Seismicity at Volcanoes: The Ischia Island (Italy) Case

Transient seismicity at active volcanoes poses a significant risk in addition to eruptive activity.
This risk is powered by the common belief that volcanic seismicity cannot be forecast, even on a long
term. Here we investigate the nature of volcanic seismicity to try to improve our forecasting capacity. To this
aim, we consider Ischia volcano (Italy), which suffered similar earthquakes along its uplifted resurgent
block. We show that this seismicity marks an acceleration of decades‐long subsidence of the resurgent block,
driven by degassing of magma that previously produced the uplift, a process not observed at other
volcanoes. Degassing will continue for hundreds to thousands of years, causing protracted seismicity and
will likely be accompanied by moderate and damaging earthquakes. The possibility to constrain the future
duration of seismicity at Ischia indicates that our capacity to forecast earthquakes might be enhanced when
seismic activity results from long‐term magmatic processes, such as degassing.