Since the settlement of the archipelago, in the fifteenth century, 31 destructive earthquakes and 28 volcanic eruptions have been registered in the Azores. Major earthquakes occurring in historical times have reached magnitudes .7, often triggering landslides and even small tsunamis. In the same period, subaerial volcanic eruptions have ranged from Hawaiian to sub-Plinian, sometimes with a hydromagmatic character, while submarine eruptions have been Azorean to Surtseyan in style. The temporal and spatial distributions of major historical events are presented and their impacts summarized.The instrumental seismic activity registered since 1980 is discussed taking into account the main volcano-tectonic structures. These seismological data allow us to improve the characterization of the present-day boundary between the Eurasia and Nubia lithospheric plates, herein defined as the East Azores Volcano-Tectonic System. The seismological data also suggest that the location of the Azores Triple Junction is to the west of Faial Island, at about 388 50 0 N, 308 25 0 W, in agreement with proposals made by other authors using aeromagnetic data. A natural seismic gap, centred in the São Jorge structural alignment, is recognized and is interpreted as a zone of stress accumulation with the potential to generate a high-magnitude earthquake similar to that of 1757.

Abstract. The Azores are an active volcanic region that offers exceptional conditions for nature-based tourism, one of the main axes of economic growth in the archipelago. A future volcanic eruption may have long-term consequences to this economic sector. Therefore, it is fundamental to assess its vulnerability to volcanic hazards in order to try to mitigate the associated risk. This study proposes a new approach to assessing the economic impact of explosive eruptions on the tourism sector. We considered two eruptive scenarios for Fogo volcano (São Miguel Island), the most probable (Volcanic Explosivity Index, VEI, 4 sub-Plinian eruption) and the worst-case (VEI 5 Plinian eruption), both producing tephra fallout and pyroclastic density currents. The results of numerical simulations were overlaid with tourism-related buildings and infrastructure of Vila Franca do Campo municipality to identify the elements at risk. The loss present value method was used to estimate the benefits generated by the accommodation units over 30 years for different economic scenarios. The assessment of the economic impact using 2018 indicators reveals that in a near-total-destruction scenario, the economic loss is approximately EUR 145 million (considering a 2 % discount rate). This approach can also be applied to other volcanic regions, geologic hazards and economic sectors.

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Volcano Observatories (VOs) around the world are required to maintain surveillance of their volcanoes and inform civil protection and aviation authorities about impending eruptions. They often work through consolidated procedures to respond to volcanic crises in a timely manner and provide a service to the community aimed at reducing the potential impact of an eruption. Within the International Airways Volcano Watch (IAVW) framework of the International Civil Aviation Organisation, designated State Volcano Observatories (SVOs) are asked to operate a colour coded system designed to inform the aviation community about the status of a volcano and the expected threats associated. Despite the IAVW documentation defining the different colour-coded levels, operating the Aviation Colour Code (ACC) in a standardised way is not easy, as sometimes, different SVOs adopt different strategies on how, when, and why to change it. Following two European VOs and Volcanic Ash Advisory Centres (VAACs) workshops, the European VOs agreed to present an overview on how they operate the ACC. The comparative analysis presented here reveals that not all VOs in Europe use the ACC as part of their operational response, mainly because of a lack of volcanic eruptions since the ACC was officially established, or the absence of a formal appointment as an SVO. We also note that the VOs, which do regularly adopt ACC, operate differently depending on the frequency and styles of eruptions, the historical eruptive activity, the nature of the unrest, the monitoring level, and also on the agreement they may have with the local Air Transport Navigation providers. This study shows that even though the ACC system was designed to provide a standard, its usage strongly depends on the evaluation of the actors responding to the volcano emergencies. Some common questions have been identified across the different (S)VOs that will need to be addressed by ICAO in order to have a more harmonised approach and usage of the ACC.

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