Exposure of Chilean Tailings to Earthquake Hazards from Potentially Seismogenic Crustal Faults

Abstract

Eighty-two percent of sand tailings dam incidents in Chile since 1915 have been seismically induced, including that which led tothe 1965 El Cobre disaster. Subduction earthquakes (magnitudes 7.5+, return periods 10s−100s of years) have been traditionallyregarded as representing the principal seismic hazard in the country and characteristically produce moderate, but widespread,damage. In contrast, much shallower earthquakes may be generated by potentially seismogenic crustal faults (PSCFs); these haverelatively lower maximum magnitudes (7.0−7.5) and longer return periods (100s−1000s of years), yet are capable of producingextensive local damage within 5 km of the fault rupture. To our knowledge, a systemic study of the exposure of tailings storagefacilities (TSFs) to earthquakes that could be generated by PSCFs has not been undertaken in Chile. Our study has filled this gapthrough integrating two publically available data sets: the 2016 national tailings database of SERNAGEOMIN and the catalogue ofPSCFs published by the South America Risk Assessment Project of the Global Earthquake Model. There are 696 registered TSFsof varying size, age, operational status and construction type distributed throughout central and northern Chile. Of these, 91 liewithin 5 km of a PSCF and 17 have been authorized to store volumes of tailings >106 m3. In order to constrain the exposure of TSFsmore robustly, a deterministic seismic hazard assessment along each major PSCF is now being undertaken. The completeness ofthe study is limited by the fact that it is anticipated that most PSCFs have poorly known fundamental fault parameters (e.g., sliprates and recurrence times), which have only been investigated systematically over the last 10 years. Despite that, recent largeearthquakes nucleated on previously unidentified PSCFs have raised awareness of their potential hazard. Our main conclusion isthat complete seismic risk assessments of TSFs in Chile must incorporate PSCFs.