ALBERT

Description: The magnitude-8.8 Maule (Chile) earthquake of 27 February 2010 ruptured a segment of the Andean subduction zone megathrust that has been suspected to be of high seismic potential. It is the largest earthquake to rupture a mature seismic gap in a subduction zone that has been monitored with a dense space-geodetic network before the event. This provides an image of the pre-seismically locked state of the plate interface of unprecedentedly high resolution, allowing for an assessment of the spatial correlation of interseismic locking with coseismic slip. Pre-seismic locking might be used to anticipate future ruptures in many seismic gaps, given the fundamental assumption that locking and slip are similar. This hypothesis, however, could not be tested without the occurrence of the first gap-filling earthquake. Here we show evidence that the 2010 Maule earthquake slip distribution correlates closely with the patchwork of interseismic locking distribution as derived by inversion of global positioning system (GPS) observations during the previous decade. The earthquake nucleated in a region of high locking gradient and released most of the stresses accumulated in the area since the last major event in 1835. Two regions of high seismic slip (asperities) appeared to be nearly fully locked before the earthquake. Between these asperities, the rupture bridged a zone that was creeping interseismically with consistently low coseismic slip. The rupture stopped in areas that were highly locked before the earthquake but where pre-stress had been significantly reduced by overlapping twentieth-century earthquakes. Our work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future great earthquakes, which thus might be anticipated by geodetic observations.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Moreno, Marcos -- Rosenau, Matthias -- Oncken, Onno -- England -- Nature. 2010 Sep 9;467(7312):198-202. doi: 10.1038/nature09349.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Telegrafenberg, Potsdam 14473, Germany.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20829792" target="_blank"〉PubMed〈/a〉

Description: On 1 April 2014, Northern Chile was struck by a magnitude 8.1 earthquake following a protracted series of foreshocks. The Integrated Plate Boundary Observatory Chile monitored the entire sequence of events, providing unprecedented resolution of the build-up to the main event and its rupture evolution. Here we show that the Iquique earthquake broke a central fraction of the so-called northern Chile seismic gap, the last major segment of the South American plate boundary that had not ruptured in the past century. Since July 2013 three seismic clusters, each lasting a few weeks, hit this part of the plate boundary with earthquakes of increasing peak magnitudes. Starting with the second cluster, geodetic observations show surface displacements that can be associated with slip on the plate interface. These seismic clusters and their slip transients occupied a part of the plate interface that was transitional between a fully locked and a creeping portion. Leading up to this earthquake, the b value of the foreshocks gradually decreased during the years before the earthquake, reversing its trend a few days before the Iquique earthquake. The mainshock finally nucleated at the northern end of the foreshock area, which skirted a locked patch, and ruptured mainly downdip towards higher locking. Peak slip was attained immediately downdip of the foreshock region and at the margin of the locked patch. We conclude 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 final failure, distinguishing the Iquique earthquake from most great earthquakes. Finally, only one-third of the gap was broken and the remaining locked segments now pose a significant, increased seismic hazard with the potential to host an earthquake with a magnitude of 〉8.5.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Schurr, Bernd -- Asch, Gunter -- Hainzl, Sebastian -- Bedford, Jonathan -- Hoechner, Andreas -- Palo, Mauro -- Wang, Rongjiang -- Moreno, Marcos -- Bartsch, Mitja -- Zhang, Yong -- Oncken, Onno -- Tilmann, Frederik -- Dahm, Torsten -- Victor, Pia -- Barrientos, Sergio -- Vilotte, Jean-Pierre -- England -- Nature. 2014 Aug 21;512(7514):299-302. doi: 10.1038/nature13681. Epub 2014 Aug 13.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉GFZ Helmholtz Centre Potsdam, German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany. ; School of Earth and Space Sciences, Peking University, Beijing 100871, China. ; Centro Sismologico National, Universidad de Chile, Facultad de Ciencias Fisicas y Matematicas, Blanco Encalada 2002, Santiago, Chile. ; Institut de Physique du Globe de Paris, 1, rue Jussieu, 75238 Paris cedex 05, France.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25119049" target="_blank"〉PubMed〈/a〉