Contrasting seismic risk for Santiago, Chile, from near-field and distant earthquake sources

More than half of all the people in the world now live in dense urban centres. The rapid expansion of cities, particu-larly in low-income nations, has enabled the economic and social development of millions of people. However, many of thesecities are located near active tectonic faults that have not produced an earthquake in recent memory, raising the risk of losingthe hard-earned progress through a devastating earthquake. In this paper we explore the possible impact that earthquakes canpose to the city of Santiago in Chile from various potential near-field and distant earthquake sources. We use high resolution stereo satellite imagery and derived digital elevation models to accurately map the trace of the San Ramón Fault, a recentlyrecognised active fault located along the eastern margins of the city. We use scenario based seismic risk analysis to compare andcontrast the estimated damage and losses to the city from several potential earthquake sources and one past event, comprising i)rupture of the San Ramón Fault, ii) a hypothesised buried shallow fault beneath the centre of the city, iii) a deep intra-slab fault,and iv) the 2010 Mw 8.8 Maule earthquake. We find that there is a strong magnitude-distance trade-off in terms of damage and losses to the city, with smaller magnitude earthquakes on more local faults, in the magnitude range 6-7.5, producing 9 to17 times more damage to the city and estimated fatalities compared to the great magnitude 8+ earthquakes located offshore onthe subduction zone. Our calculations for this part of Chile show that unreinforced masonry structures are the most vulnerableto these types of earthquake shaking. We identify particularly vulnerable districts, such as Ñuñoa, Santiago and Macul, wheretargeted retrofitting campaigns would be most effective at reducing potential economic and human losses. Due to the potency of near-field earthquake sources demonstrated here, our work highlights the importance of also identifying and consideringproximal minor active faults for cities in seismic zones globally, in addition to the more major distant large fault zones that aretypically focused on in the assessment of hazard.