Déformations post-sismiques après le séisme de Maule (Mw8.8, Chili, 2010) : mesures GPS et modélisation en éléments finis pour une asthénosphère viscoélastique

Abstract : The study of giant earthquakes on subduction zone represents a main interest. They are indeedsufficiently powerful to excite the mantle and trigger its viscoelastic relaxation, over a very largespatial (thousands of kilometers) and temporal (several decades) scale. Postseismic deformation,monitored by spatial geodesy, are a proxy to the geometrical and rheological characteristics of thesubduction interface, that will allow us to study the whole seismic cycle.On February 27th 2010 in the region of Maule, Chile, occurs the Mw 8.8 megathrust earthquake.Yet, the subduction of the Nazca plate beneath the continental South-American plate offers, forthe first time, the opportunity to measure continuously and densely the postseismic deformationfollowing the earthquake, over more than 1500 km. Otherwise, more than a decade of GPS repeatedmeasurements allowed to image a very heterogeneous coupling all along the Chilean interface. Thevisible imbrication between postseismic deformation and interseismic loading, supported by historicaland instrumental seismicity, highlights interactions between the segments. Viscoelastic modelsof seismic cycle appears to be the only way to understand these interactions.This PhD focused on two main axes, that will lead to the development of viscoelastic modelsof seismic cycle. The first part was dedicated to the study of postseismic deformation followingthe Maule earthquake. Therefore, we processed and analyzed very precisely GPS data in orderto extract the postseismic pattern and modeled it using the finite elements method. A combinedmodel of afterslip and viscoelastic relaxation in the asthenosphere and in a low viscosity channel,extending deep along the slab, can reproduce the complex deformation pattern, horizontaly and inverticaly. The amplitude and complexity of the near-field deformation result from aseismic slip onthe fault plane, while the great uplift of the Cordillera is reproduced by relaxation in the channel.The far field extension, up to 1600 km, entirely results from relaxation in the asthenosphere. Onthe other hand, the continuity of campaign measurements was the occasion to fill the ultimate gapof data, and thus estimate a continuous interseismic velocity field from the North of the Maulerupture zone up to North Chile. Finally, even if the final viscoelastic models of seismic cycle couldnot be processed yet, the present postseismic model already brings new insights on interactionsbetween the different segments of the Chilean interface, following the last Chilean earthquake.
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Emilie Klein. Déformations post-sismiques après le séisme de Maule (Mw8.8, Chili, 2010) : mesures GPS et modélisation en éléments finis pour une asthénosphère viscoélastique. Sciences de la Terre. Ecole normale supérieure - ENS PARIS, 2015. Français. ⟨NNT : 2015ENSU0046⟩. ⟨tel-01600011⟩

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