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

<p>Transient seismicity at active volcanoes poses a significant risk in addition to eruptive activity.<br>This risk is powered by the common belief that volcanic seismicity cannot be forecast, even on a long<br>term. Here we investigate the nature of volcanic seismicity to try to improve our forecasting capacity. To this<br>aim, we consider Ischia volcano (Italy), which suffered similar earthquakes along its uplifted resurgent<br>block. We show that this seismicity marks an acceleration of decades&#8208;long subsidence of the resurgent block,<br>driven by degassing of magma that previously produced the uplift, a process not observed at other<br>volcanoes. Degassing will continue for hundreds to thousands of years, causing protracted seismicity and<br>will likely be accompanied by moderate and damaging earthquakes. The possibility to constrain the future<br>duration of seismicity at Ischia indicates that our capacity to forecast earthquakes might be enhanced when<br>seismic activity results from long&#8208;term magmatic processes, such as degassing.</p>