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Study of mechanical properties and transient deformation at subduction zones from analysis of seismic activity, the case of Chile.


IPGP - Îlot Cuvier


Soutenances de thèses


Florent Aden-Antoniow

Sismologie (SIS)

Subduction zones are the most seismically active regions in the world. They are also the seat of megathrust-earthquakes such the chilean earthquake of 1960, magnitude 9.5. The last major ruptures in Chile have revealed complex seismic-aseismic interactions. In order to study these interactions, we investigated two seismic crises: the seismic swarm of April 2017 and 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 which is known to have experienced mega-earthquakes in the past (in 1730 and in 1906). In order to study the dynamics of this swarm, we 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. This seismic activity was accompanied by a gradual slip along the interface that we observed both in the GPS data and by detecting repeating-earthquakes. Our analysis suggests that the swarm was driven by aseismic slip. The second study concerns an earthquake of magnitude 8.2 which occurred on April 1 st 2014 near the city of Iquique. This event broke one-third of the seismic gap in northern Chile. It was preceded by a sequence of precursor seismic swarms that appeared to have been accompanied by stable slip in the subduction interface. By building a more complete earthquake catalog (>30000 events), we were able to thoroughly analyse the preparatory phase of the Iquique earthquake. Following a statistical approach, we observe the occurrence of a large-scale seismic quiescence in the region of the mainshock before its nucleation. We link this quiescence to a downdip transient-slip potentially related to fluid channeling along the subduction interface.