Vertical evacuation as a tsunami risk mitigation measure in Chile

CIGIDEN has studied in detail the possible effects of earthquakes and tsunamis on the coastal edge of Chile, making crosses between variables of intensity of these threats with evacuation conditions. The scenarios analyzed account for the need to advance regulations and standards that allow vertical evacuation to be incorporated into the mitigation options that the authority may consider. In this document, we summarize some background that shows the state of the art of the potential for tsunami evacuation in coastal cities, making, by way of example, a diagnosis for Viña del Mar. To this end, we contextualize the threat of tsunamis presented by the central coast of Chile, analyzing the current evacuation strategies in the area, contrasting them with the alternative of evacuating vertically.

The results of this diagnosis motivated a review of international experience with vertical evacuation, which is complemented by recent experiences of the impact of tsunamis on buildings designed under Chilean regulations. Based on the research carried out, recommendations were made regarding the criteria that should be considered before implementing vertical evacuation plans at the national level.

First, morphological characteristics should be taken into account: (1) the site of sites for the construction of vertical evacuation buildings; (2) the minimum amount of evacuation area to be provided of at least 0.93 m2 per person in accordance with FEMA recommendations (2008); (3) an adequate number of accesses with appropriate characteristics (visibility from the outside, dimensions) should be envisaged; and (4) an internal circulation system suitable for operation should be included.

Second, the characteristics of occupation and management: (1) the free access of the population during an emergency should be ensured; (2) trained personnel must be in place to guide the population; (3) a tax subsidy or reduction programme should be established in the case of private buildings used as shelters; (4) a regular review programme is required
for these buildings; and (5) citizen linkage and participation strategies should be established to promote the good use and care of these infrastructures.

Third, structural considerations of buildings must be verified to ensure proper performance against the effects of the earthquake and tsunami. Finally, the fourth aspect to consider is the assessment of the geotechnical response conditions of the soil. The recommendations presented above aim to contribute to discussions regarding the definition of criteria, regulations or standards that allow the implementation of vertical evacuation in Chile.