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This work analyses the issue of the acceptable level of risk in the civil protection field from a behavioural perspective. Choosing the acceptable level of risk for a community is a task that political decision-makers are charged with. However, it so happens that politicians do not manage to accomplish this. The reasons for this and some possible solutions have been broached by Di Bucci and Savadori (2018). Starting from that paper, this work aims at proposing some preliminary reasoning on the so-called L'Aquila trial, which involved scientists and Civil Protection officers after the 6 April 2009 Abruzzo earthquake (Italy). Behavioural sciences provide a key to understanding what happened through heuristics and biases that affected all the actors in this story, including the local population, the media, and judiciary, in the frame of coming to no practical decision about the acceptable level of risk. The conclusion is that scientific, technical, and professional communities could and should foster the awareness of people, the media, and political decision-makers (and judiciary), and allow the communities and their decision-makers to take on participated and shared decisions on their acceptable level of risk. These should include the consequences of their decisions and, in a broader perspective, the residual risks that, in a general appraisal, they will decide to accept. [ABSTRACT FROM AUTHOR]

Over the past few years the assessment of the earthquake potential of large continental faults has increasingly relied on field investigations. State-of-the-art seismic hazard models are progressively complementing the information derived from earthquake cat- alogues with geological observations of active faulting. Using these observations, however, requires full understanding of the relationships between seismogenic slip at depth and surface deformation, such that the evidence indicating the presence of a large, potentially seismogenic fault can be singled out effectively and unambiguously. We used observations and models of the 6 April 2009, Mw 6.3, L'Aquila, normal faulting earthquake to explore the relationships between the activity of a large fault at seismogenic depth and its surface evidence. This very well-documented earthquake is representative of mid-size yet damaging earthquakes that are frequent around the Mediterranean Basin, and is somehow paradigmatic of the nature of the associated geologic evidence along with observational difficulties and ambiguities. Thanks to available high-resolution geologic, geodetic and seismological data aided by analogue modeling, we reconstructed the full geometry of the seismogenic source in relation with surface and sub-surface faults.We find that the earthquake was caused by seismogenic slip in the range 3-10 km depth, and that the slip distribution was strongly controlled by inherited discontinuities. We also contend that faulting was expressed at the surface by pseudo-primary breaks resulting from coseismic crustal bending and by sympathetic slip on secondary faults. Based on our results we propose a scheme for hierarchizing normal faults through which all surface occurrences related to faulting at depth can be interpreted in the frame of a single, mechanically coherent model. Appreciating such complexity is crucial to avoid severe over- or under-estimation of the local seismogenic potential. [ABSTRACT FROM AUTHOR]