Risk perception and social vulnerability to earthquakes in Grenoble (French Alps)

The city of Grenoble (French Alps) is characterized by a rather low seismicity as well as a tectonic context prone to the occurrence of major earthquakes (M = 6). The population is therefore not used to experiencing earthquakes: this can lead to a low culture of risk, which may imply a rather high vulnerability of the population. Consequently, it is necessary to better evaluate vulnerability and to find ways of reducing it. Social vulnerability is usually evaluated through surveys focusing on residential population. When these studies are carried out by geographers, they sometimes take into account a spatial dimension by mapping the results. Here, a temporal dimension is also integrated and residents as well as users of the city, i.e. users with any activity as working, shopping, having leisure time, etc. are surveyed. The method consists in building a social and spatial representative sample through three dimensions: social (age), temporal (hour of the day) and spatial (place of residence or activity). For this reason the household travel survey was used to build the sample. The risk perception survey shows that only 16% of the sample feel exposed to earthquakes. The youngest, most qualified, the students and working people seem to better know the adequate safety measures to be taken in case of an earthquake. Besides classic statistical analyses, the answers to the questionnaire were synthesized into a vulnerability index. Once more, the most qualified are characterized by a lower vulnerability. The cartography of the survey results provides interesting conclusions for authorities in charge of risk mitigation, who could then concentrate their preventive information campaign on certain districts or social groups. Among other conclusions, these maps highlight the gap between the physical vulnerability of buildings and the confidence of the population in their resistance in case of an earthquake.