The Pisagua earthquake, which took place on 1st of April 2014 offshore the coast of Chile, broke part of the so-called northern Chile seismic gap, the last segment of the South American plate boundary that had not ruptured in the last century. For this reason, the region has been monitored closely with various instruments for several years now. The Integrated Plate boundary Observatory Chile (IPOC), in which GFZ is the coordinating partner, comprises broadband seismometers, accelerometers, GNSS (Global Navigation Satellite System) stations, and strain meters, amongst others. Evaluation of the data from these instruments enabled not only the development of a model for the spatial and temporal evolution of the main shock and the largest aftershock (white contour lines in the left panel), but also derivation of the long-term coupling state of the tectonic plates (background coloring). Furthermore, statistical analysis of the foreshock activity (blue dots) revealed a decrease of its b-value, which describes the ratio of the frequency between larger and smaller quakes (lower right panel). These observations lead to the conclusion that gradual weakening of the central part of the seismic gap, accentuated by the foreshock activity in a zone of intermediate seismic coupling, was instrumental in causing failure of the plate boundary. This insight distinguishes the Pisagua earthquake from most great earthquakes. Finally, it is noteworthy that the earthquake ruptured only part of the previously-locked segment; the remaining locked part now poses a significant and increased seismic hazard, with the potential to host an earthquake of magnitude larger than 8.5.
| Nature | DOI: /10.1038/nature13681 |