Earthquakes present a major threat to Chile's population and built environment. Some of the world's largest earthquakes occur in a subduction zone that extends along the country's 3000 km coastline. There the floor of the Pacific Ocean is being pushed beneath the continental edge of South America, giving rise to major earthquakes and volcanoes. The largest earthquake ever recorded, magnitude 9.5 in 1960, ruptured the subduction zone along the southern third of the country south of Concepción. More than ten earthquakes greater than magnitude 8.2 have occurred in Chile over the past century, including recent events of magnitude 8.8 in 2010 (Maule, February 27), 8.2 in 2014 (Iquique, April 1), and 8.3 in 2015 (Illapel, September 16) (Figure 1).

The experience during the Maule earthquake in 2010 made it obvious that significant improvements to the infrastructure in Chile for earthquake monitoring and reporting were required both to meet the nation's needs in hazard response and to serve the global seismological community as a natural laboratory to study major earthquake and tsunami processes. With support from this NSF award, the IRIS Consortium collaborated with the University of Chile to install ten modern "Global Reporting Observatories" (GRO-Chile) at 300 km intervals along the length of Chile (Figure 2) to provide an initial backbone for a new national monitoring network. The instrumentation and installation procedures for these stations are based on the experience gained with the USArray Transportable Array stations of the NSF-funded EarthScope project in the United States. Each of the GRO-Chile stations is equipped with an extensive complement of geophysical sensors – broadband seismometers and accelerometers to capture the full spectrum of ground motions; barometric pressure and infrasound sensors to record atmospheric disturbances; and meteorological sensors to record weather conditions – along with power and telemetry systems to provide real-time relay of all data to a central data collection center in Santiago (Figure 3). With funding from the government of Chile, an additional 75 seismic, 100 GPS geodetic, and 120 strong motion stations have been added to complete the observational component of the new national network. The University of Chile also worked with the USGS National Earthquake Information Center to develop modern procedures for data processing and analysis and with Chilean disaster response agency (Oficina Nacional de Emergencia del Ministerio del Interior, ONEMI) to enhance the earthquake alerts and tsunami warnings to the public. As a result of these improvements, accurate earthquake locations are now available within minutes of their occurrence and the national response to the significant earthquakes in 2014 and 2015 was substantially better than for any previous events.

In addition to its broader impacts in terms of enhanced earthquake safety in Chile, these improvements in technical capability have produced significant advances in the quality and quantity of data available for scientific research on the process of earthquake generation in subduction zones. Significant improvements in resolution of the spatial and temporal distribution of small and large earthquakes are possible because of the denser spacing of stations. Finer details of the time-history of displacements during large earthquakes can be derived from the higher fidelity of recorded ground motions. The enhanced data can also be used to produce higher quality images of the structure of the Earth's interior in this complex zone of interaction between oceanic and continental plates. Improvements in our understanding of earthquakes in the subduction zone beneath Chile have special relevance for earthquake safety in the United States because of potential for large earthquakes produced by similar processes in the Cascadia region of the Pacific Northwe...

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