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

¿Urbanización fallada? La Falla San Ramón como nuevo escenario de riesgo sísmico y la sostenibilidad de 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.Santiago de Chile, habitada por cerca de 7 millones de personas, se ubica a los pies del flanco occidental de la Cordillera Principal de Los Andes, uno de los cordones montañosos más activos de nuestro planeta. La zona oriente de Santiago ha experimentado una expansión urbana sin precedentes en las últimas cuatro décadas, generando un aumento de la exposición de sus habitantes a riesgos socio-naturales de origen geológico, entre ellos la posibilidad de terremotos corticales asociados a la Falla San Ramón. El presente trabajo explora este nuevo escenario de amenaza sísmica, utilizando cartografía especializada a partir de cinco estados de avance claves para la ciudad, impulsados por políticas urbanas nacionales e instrumentos de planificación intercomunal desde 1960 hasta la actualidad. Los resultados muestran que esta urbanización acelerada ha alcanzado un 55% de la traza en superficie de la falla, lo cual no ha sido considerado en las regulaciones. Se concluye en la necesidad de avanzar en los vacíos normativos a través de la articulación de la amenaza sísmica natural con el medio urbano, como base para la reducción del riesgo de desastres y un desarrollo sostenible que considere además las inequidades de la urbe