Séisme Offshore d’Illapel, Chili, Mw 8.2 à 8.4

Read in french INSU/CNRS web page on the Sept 2015 Illapel earthquake: http://www.insu.cnrs.fr/node/5444

Reports of 2013 and 2014 activities and results

New "Reports" page giving access to detailed description of activities and results.

Une équipe internationale étudie l'aléa sismique de Santiago du Chili

Le potentiel sismique du chevauchement ouest andin, identifié en 2010 comme la structure majeure responsable de la surrection de la chaîne des Andes était jusqu'à maintenant très mal connu. Une équipe internationale, associant des chercheurs de l'Université du Chili, de l'Institut de Physique du Globe de Paris et de l'IRSN en France, des Universités de San Diego et de Waco aux USA, révèle que le segment de ce chevauchement, localisé au cœur même de Santiago, capitale du Chili, a rompu deux fois, depuis environ 18000 ans, lors de séismes d’une magnitude pouvant atteindre Mw7.5. Cette étude, soutenue en partie par l'ANR MegaChile, a été publiée cette semaine dans la revue GEOLOGY et montre que la capitale Chilienne est soumise a un risque sismique majeur. 

Page CNRS-INSU sur le sujet.

Probing large intra-plate earthquakes at the west flank of the Andes, G. Vargas, Y. Klinger, T.K. Rockwell, S.L. Forman, S. Rebolledo, S. Baize, R. Lacassin, and R. Armijo .  Geology, publié en ligne le 17 octobre, 2014. doi: 10.1130/G35741.1  PDF (open access CC-BY license)

Megathrust ruptures in North Chile

NEW publication :
Ruiz, S, Metois, M, Fuenzalida, A, Ruiz, J, Leyton, F, Grandin, R, Vigny, C, Madariaga, R, Campos, J,Intense foreshocks and a slow slip event preceded the 2014 Iquique Mw 8.1 earthquake, SCIENCE, 345, 6201, 1165-1169, 2014. 

A great earthquake, with magnitude between 8.0 (Geoscope-Scardec) and 8.2 (USGS) has occurred on 1 April 2014 in northern Chile (local time, or 2 April 2014 UTC). The main event was followed 24 hours later by a magnitude 7.6 earthquake. These earthquakes have broken the subduction interface that marks the separation between the Nazca oceanic plate and the South American continental plate

Seismo-tectonic context of the April 2014 earthquakes. The epicenter of the mainshock (magnitude 8.2) is indicated in red. The orange dots represent the location of epicenters of the magnitude 7.6 earthquake and aftershocks occurring within 10 days of the mainshock (from USGS). Color lines show the location and length of past earthquakes (from Bejar et al., 2010). The Arica gap is defined by the inferred rupture of the 1877 earthquake (with significant uncertainty on the extent of 19th century earthquake ruptures).

Two seismic gaps were  identified since several decades in northern and in central/southern Chile, and seemed to be ready for a forthcoming rupture : the Arica gap to the North, which was the site of a magnitude 8.8 earthquake in 1877, and the Concepción gap, where another massive earthquake occurred in 1835. This latter gap ruptured in 2010 (Maule earthquake), which likely corresponds to the end of a full ~175 years cycle in the area. On the other hand, the Arica gap seems to start to break in a more progressive manner. It first ruptured in its deeper part, and for a short length, in 2007 during the Tocopilla earthquake (magnitude 7.7). The April 2014 earthquakes also broke a part of the Arica gap, this time over a length of 150 km to 200 km, and closer to the surface. Importantly, The subduction segment that has just broken in Chile was showing an unusually high level of seismic activity in the few last months. This seismic unrest was characterized by a series of "seismic swarms", with the very last crisis dating back from March 2014 only.

These earthquakes have contributed to an increase in the stress acting on the neighboring segments of the mega-thrust, to the north and to the south of the segment that has just broken. The probability that earthquakes of similar type, with magnitudes exceeding 8.0 or more, in the next days, weeks or years, is therefore rather high. Currently, it is impossible to exclude the possibility that another "giant" earthquake, with magnitude 8.5 up to 9.0, could break the whole remaining segments of the Arica gap, to the north up to Peru, and to the south down to the Mejillones peninsula (located to the north of the city of Antofagasta).

MegaChile researchers are deeply involved in the study of the April 2014 earthquakes within the framework of the Associated Laboratory "Montessus de Ballore", which gathers ENS, IPGP, and the University of Chile. A joint IPGP-ENS team is currently participating to a survey in the field in order to measure the precise location of GPS markers, within a survey program coordinated by the Geophysics Department of the University of Chile. More actions (seismology, geodesy,  tectonics) are under way.

Read more on IPGP special page, GEOSCOPE pages for the main earthquake (M8) and for the  magnitude 7.6 event, INSU-CNRS special pages : " page séisme au Chili " and " un point plus complet sur les informations scientifiques " (both in french)

Project Kick-Off

The MegaChile project is funded by the Agence Nationale de la Recherche (ANR). It will last from november 2012 to the end of 2015. MegaChile is chaired by two partners - the Laboratoire de Géologie from the ENS Ulm and the Institut de Physique du Globe de Paris (IPGP) - that host most of the researchers involved in the project. The project has strong links with the Laboratoire International Associé (LIA) Montessus de Ballore (CNRS-INSU), and with the University of Chile in Santiago.

The project kick-off meeting took place at the ENS on January 28th with the presence of 17 researchers. A draft report summarizing the presentation and the discussions that occurred during the meeting, is available as a PDF document. Keynote PDFs of presentation of the four Work Packages are available from the Private zone of this web site.