Misleading urbanization? The San Ramon fault as a new seismic risk scenario and the sustainability of Santiago, Chile

Santiago, capital city of Chile inhabited by ca. 7 million persons (INE, 2018), is located at the foot of the western flank of the main Andes Cordillera, which is one of the most active mountain chains worldwide. The eastern border of the city, located at the piedmont of the mountain front, experienced an accelerated urbanization in the last four decades with respect to the previous four centuries, with subsequent increased risk associated to geological hazards among of them the possibility for crustal earthquakes along the active San Ramon thrust fault system. Here, we explore this new seismic risk scenario by comparing first order urban mapping at different stages of the horizontal expansion of the city, including the location of the geological structure, with urban policies developed since 1960. Our results show that -at present- urbanization reached 55% of the San Ramon fault trace, evidencing that this active geological structure has not been considered in urban regulations developed for the metropolitan region. We conclude the necessity to unravel normative and knowledge gaps in order to relate the natural geological hazard with the urban planning, as an opportunity to progress toward a sustainable development of the mega-city of Santiago