Fluids supplied by stored magma at depth are causal factors of volcanic unrest, as they can cause pressurization/heating of hydrothermal systems. However, evidence for links between hydrothermal pressurization, CO₂ emission and volcano seismicity have remained elusive. Here, we use recent (2010−2020) observations at Campi Flegrei caldera (CFc) to show hydrothermal pressure, gas emission and seismicity at CFc share common source areas and well-matching temporal evolutions. We interpret the recent escalation in seismicity and surface gas emissions as caused by pressure-temperature increase at the top of a vertically elongated (0.3–2 km deep) gas front. Using mass (steam) balance considerations, we show hydrothermal pressurization is causing energy transfer from the fluids to the host rocks, ultimately triggering low magnitude earthquakes within a seismogenetic volume containing the hydrothermal system. This mechanism is probably common to other worldwide calderas in similar hydrothermal activity state.

储存的岩浆在深度提供的流体是火山活动的原因，因为它们会引起热液系统的增压/加热。然而，有证据表明CO ₂与水热加压之间存在联系排放和火山的地震活动性仍然难以捉摸。在这里，我们使用Campi Flegrei火山口（CFc）的最新观测（2010-2020年）来显示CFc的热液压力，气体排放和地震活动具有共同的震源区和相称的时间演化。我们将地震活动和地表气体排放量的最近升高解释为由于垂直延长（深0.3–2 km）的天然气锋顶部的压力-温度升高而引起的。使用质量（蒸汽）平衡考虑因素，我们显示出热液加压导致能量从流体传递到主体岩石，最终在包含热液系统的地震成因区内引发了低级地震。这种机制可能是处于类似热液活动状态的全球其他火山口所共有的。