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  Thèse de Sandro Vaca

Links between earthquakes and slow deformations in Ecuador
Encadrant (et co-encadrant) : 
Jean Battaglia (LMV, Clermont-Ferrand, France)
Jean-Mathieu Nocquet (Géoazur, Nice, France)
Résumé: 

In the Ecuadorian margin, the convergence of Nazca and South-American plates was the source for the occurrence of strong earthquakes in the last century. Nowadays, the relation between the mechanisms for the stress accumulation and its later release, as the source of those earthquakes, is better described and understood thanks to the installation of the “ADN” seismic and geodetic networks (French-Ecuadorian Project), at the end of 2008.

The studies on subductions zones around the world show that the stress accumulation and its release is more complex than this one predicted by the simple seismic-cycle model, which postulate that the stress is continuously saved, before a sudden release generating a strong earthquake. In particular the slow slip events (SSE) occurrence (duration of days or months), discovered in the 90’s in Canada and Japan, shows that the seismogenesis in the subductions zone are more complex than the scientist though.

The first observations on this kind of phenomena in the Ecuadorian margin showed the existence of SSEs in the northern of Ecuador (Esmeraldas region) and central margin (La Plata Island). These SSEs modify the stress state and trigger abundant seismicity such as the 2010 SSE episode near to La Plata Island (Vallée et al, 2013). In this case the associated seismicity did not present a main shock and was distributed in clusters of similar events (seismic swarm forming family events). So, most of this study, as was done on other subductions zones, is addressed to detect and describe this type of sequences based on the analysis of the associated seismic-signals since 2008 for the Ecuadorian margin (i.e. seismic swarms, tremors, etc). The required analysis includes technics of correlation of continuous waveforms, location and waveform inversion. Also, the spatio-temporal evolution of the seismicity could be compared with the displacements detected with the geodesy and determines the seismic and aseismic relations. Additionally, this study aims to complement with the focal mechanisms determination by using waveform inversion method, to better characterize the geometry and rupture mechanisms of the seismic sources.

The eventual occurrence of a seism of magnitude > 5.5 in the interface zone is also considered in the subject, because it will give information about the characteristics of the coupling in the source and also will allow correlate the seismic and GPS data to better characterize the seismic source.

Date de soutenance: 
Monday 03 July 2017 - 14:00