Vers une vision intégrée du cycle sismique en zone de subduction: exemple de l’Equateur
IPGP - Îlot Cuvier
Séminaires communs Tectonique-Sismologie
Université Côte d’Azur, IRD, CNRS, Observatoire de la Côte d’Azur, Geoazur
Rapid subduction at the Ecuador-Colombia margin has generated one of the largest seismic sequence observed by modern seismology since the great 8.5-8.8 1906 earthquake. Seismological and GPS networks progressively installed since 2008 revealed the pattern of strain accumulation at the megathrust and a diversity of stress release modes. Interseismic coupling models show three different areas: (1) in northern Ecuador, high coupling north of latitude 0.5°N extending several hundreds of kilometers along strike to a ~35 km depth has been the locus of the Mw 7.7 1958 and Mw 8.2 1979 earthquakes (2) high coupling between latitudes 0.5°S to 0.5°N confined between 15 and 35 km depth experienced the Mw 7.8-7.9 earthquake and was ruptured again by the Mw 7.8 April 16 2016 Pedernales earthquake (3) south of latitude 0.5°S, weak interseismic coupling occurs, extends over ~1000 km until central Peru with small (50x50 km) shallow (<20 km) patches of high interseismic coupling. Shallow Slow Slip Events (SSE), synchronous to Seismic Swarms organized into families of repeating earthquakes occur regularly. Their locations appear to delimit the updip limit of high interseismic coupling and seismic rupture in central Ecuador, while the largest ones south of 0.5°S appear to entirely release previously accumulated strain at a shallow locked patches. Aseismic slip following the Mw 7.8 2016 Pedernales earthquake appear to occur preferentially at areas that previously underwent SSE. This finding enlightens the patchiness of the frictional anatomy of the plate interface at the Ecuador subduction zone.