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Etude des propriétés mécaniques et de la déformation transitoire dans les zones de subduction à partir de l'analyse de l'activité sismique, le cas du Chili

Abstract : The subduction zones are the most seismically active places in the world and are also the seat of megathrust-earthquakes such as the one that stroke Chile in 1960 with a magnitude estimated at 9.5. The last major ruptures in Chile have revealed complex seismic-aseismic interactions. In order to study these interactions, we investigated on at two seismic crises: the seismic swarm of April 2017; the preparatory phase of the Iquique earthquake (M w 8.1) from April 1 st , 2014. The seismic swarm took place near the city of Valparaiso in an area known to have experienced mega-earthquakes in the past: in 1730 and in 1906. In order to study the dynamics of this swarm we have built a rich catalog of more than 2000 earthquakes composing the sequence. An intense seismic activity began on April 22 nd , two days before the main earthquake of the sequence M w 6.9 and was accompanied by a gradual slip along the interface that we observed both in the GPS data and using repeating-earthquakes. Our analysis suggest that the swarm was driven by aseismic slip. The second study concerns an earthquake of mag-nitude 8.2 which occurred on April 1 st 2014 near the city of Iquique and broke one-third of the seismic gap in northern Chile. This earthquake was preceded by a sequence of precursor seismic swarms that appeared to have been accompanied by stable slip in the subduction interface as well. By building a more complete earthquake catalog, we were able to thoroughly analyze the preparation of the Iquique earthquake. We show, following a statistical approach, the occurrence of a large-scale seismic quiescence in the region of the mainshock. We link this quiescence to a downdip transient-slip potentially related to fluid channeling along the subduction interface.
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Florent Aden-Antoniów. Etude des propriétés mécaniques et de la déformation transitoire dans les zones de subduction à partir de l'analyse de l'activité sismique, le cas du Chili. Sciences de la Terre. Université Sorbonne Paris Cité, 2019. Français. ⟨NNT : 2019USPCC011⟩. ⟨tel-02533627⟩

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