Departamento de Geologia and Laboratório de Tectonofísica e Tectónica Experimental, Faculdade de Ciências da Universidade de Lisboa, Portugal

Formalised elicitation of expert judgements has been used in recent years to help tackle several problematic societal issues, including volcanic crises and pandemic threats. We present an expert elicitation exercise for Piton de la Fournaise volcano, La Réunion island, held remotely in April 2021. This involved twenty-eight experts from nine countries who considered a hypothetical effusive eruption crisis involving a new vent opening in a high-risk area. The tele-elicitation presented several challenges, but is a promising and workable option for application to future volcanic crises. Our exercise considered an “uncommon” eruptive scenario with a vent outside the present caldera and within inhabited areas, and provided uncertainty ranges for several hazard-related questions for such a scenario (e.g. probability of eruption within a defined timeframe; elapsed time until lava flow reaches a critical location, and other hazard management issues). Our exercise indicated that such a scenario would probably present very different characteristics than the eruptions observed in recent decades, and that it is fundamental to include well prepared expert elicitations in updated civil protection evacuation plans to improve disaster response procedures.

The neotectonics of the islands of Faial, Pico and S. Jorge (Azores) is presented. Preliminary paleoseismology data from trench exposures across three active fault zones (Lomba do Meio, Lagoa do Capitão and Pico do Carvão faults) complement the information. Radiocarbon age constraints of paleoearthquakes suggest clustering of surface rupturing events. Slip rates deduced from paleoseismology analysis range from 0.10 to 0.40 cm/year and validate long-term slip rates obtained by neotectonic studies (using Pleistocene markers). The studied faults allowed a preliminary seismic hazard assessment: magnitudes of the largest paleoearthquakes, determined from slip per event range from Mw = 6.9 to 7.1, and maximum expected magnitudes, estimated from rupture length or rupture area, vary from Mw = 6.4 to 6.8. The former Mw estimates are in closer agreement with the magnitude of the major historic and instrumental seismic events in the archipelago, even though the used empirical relations between magnitude and rupture parameters may not be the most adequate due to the unique tectonic setting of Azores.