Modelling inter-event times from central volcanoes at São Miguel Island (Azores)

Central volcanoes can produce a wide spectrum of volcanic eruptions, with different magmatic compositions, styles, sizes, and recurrence periods. On volcanic islands, the eruptive record of central volcanoes is often incomplete, due to the small subaerial area, irregular topography, and high erosion rates typical of these islands, generating large uncertainties about the past eruptive activity and making the estimation of eruptive parameters, recurrence times and probabilities of future eruptions very challenging.São Miguel Island (Azores archipelago) is one of these cases, where most eruptions of the three active central volcanoes (Sete Cidades, Fogo, and Furnas) are undated or poorly reconstructed. Based on the known stratigraphy, Sete Cidades volcano erupted at least 36 times in the last 15 ky, producing 24 trachytic events, almost all explosive, and 12 basaltic flank eruptions; Fogo volcano erupted at least 21 times also in the last 15 ky, producing 16 trachytic explosive eruptions and 5 basaltic flank eruptions; while Furnas volcano erupted at least 22 times over the last 17 ky, all trachytic explosive events.Here, we model eruptive event times based on the generation of synthetic catalogues that follow the known stratigraphic sequence and include the uncertainty of eruption ages. The completeness of the eruptive records of each volcano was assessed by plotting the cumulative number of eruptions in time and identifying breaks in slope, which may indicate changes in the recording rate of events, as well as possible changes in the eruptive behaviour. In the parts of catalogues after the first break-in-slope we also checked the stationarity to identify the portions of the catalogues that could be modelled by renewal models. Fitting the stationary portion of data with several renewal models allowed to identify which statistical model best describes how eruptive events occur in time. This study presents a statistical analysis where data uncertainties are accounted for to model eruptive inter-event times, estimate recurrence periods and probabilities of future eruptions. This approach is crucial for a more robust long-term assessment of volcanic hazard, providing important clues to forecast the eruptive behaviour of central volcanoes, even in cases of low-activity systems or volcanic islands, where eruptive catalogues are frequently incomplete. In the case of São Miguel this approach allowed to estimate recurrence periods and the probability of a future event for each of the three active central volcanoes of the island.