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PhD thesis - Deformation across the Andes by InSAR

par Anne SOCQUET - 20 janvier 2014

summary :

In the area extending from Antofagasta in North Chile to Arequipa in South Peru, a large subduction earthquake is pending since the end of the 19th century. In the metropolitan region of Lima, the last big earthquake occurred in 1746. These regions therefore constitute well-identified seismic gaps. The recent earthquakes in Chile in 2010 and in Japan in 2011 showed how important it is to know the interseismic loading to estimate the characteristics of the next earthquake. Indeed, the lateral variations of coupling allow identifying on one hand the coupled zones that will relax the accumulated stress during a future large earthquake and, on the other hand, the weakly coupled zones that should act as a barrier to the earthquake propagation.

Observing the surface deformation of the overriding plate allows retrieving the variations of the interseismic loading. However, in the case of the south American subduction, the deformation associated with the seismic cycle, elastic and reversible, is merged together with the internal deformation within the overriding plate. This scrambles the estimation of the interseismic loading on the subduction interface. On the other hand, characterizing the small permanent intraplate deformation is critical to test models of recent evolution of the Andean belt. It is therefore mandatory to perform a large scale mapping of the deformation, in order to determine what are the active structures in the upper plate, and how the lithospheric deformation is distributed on the various faults across the Andes.

So far, only GPS data allowed tackling these large-scale intracontinental deformation subjects. Now, ALOS2 and Sentinel satellites should acquire a dense SAR data flow in ScanSAR mode, along long strips of 400km wide. We therefore face a unique opportunity to easily cover large zones affected by intracontinental deformation. Our team has acquired lately a unique expertise in France to map tiny, space-time variations of the deformation in different tectonic contexts (subduction and large continental faults). Provided additional developments of our NSBAS software to adapt it to new satellital data, we think that multi-timescale SAR interferometry techniques applied to massive data sets are now ready to monitor large scale tectonic deformation.

This PhD subject is also based on continuous GPS networks ( 40 stations in Chile and Peru). These ground data should validate large-scale deformation measured with InSAR that, on the other hand, should provide us with a spatially continuous map of the deformation.

The scientific work during the PhD thesis will be separated into three parts :
1. The first step will be dedicated to the exploitation of existing Scan-SAR archive issued from Envisat and Alos satellites. In this goal, the PhD candidate should test ScanSAR modulus of ROI_PAC/GMTSAR and integrate them into our own processing chain NSBAS, that includes the following improvements : SLC images coregistration, tropospheric effects mitigation using ERA-Interim meteorological model, DEM errors correction and time series inversion. L-band data are prone to ionospheric effects, that we plan to reduce with different methods (band-splitting processing and image correlation).
2. The second step will be dedicated to the processing of the data flow issued from Sentinel and ALOS2 satellites, to be launched in 2014. Here again, an adaptation of our processing chain is required in order to integrate the new data formats.
3. Finally the PhD candidate will use his strain rate maps to constrain the interseismic coupling and visco-elastic models of the deformation through the Andes.

This PhD thesis should bring a significant and original contribution to our understanding of coupling mechanisms on the subduction interface, and of lithospheric deformation in this major orogene. Moreover it will permit methodological developments that should eventually allow processing routinely the data flow generated by the new generation of SAR satellites.

The access to satellital data will be made possible through existing projects between the PhD advisers and space agencies :
-  Envisat data : ESA AOE720 project, PI A. Socquet & MP Doin : « Survey of large surface deformation in the Chile-Peru Seismic Gap (South America), using ASAR interferometry »
-  ALOS data : ALOS-2 project, PI A. Socquet (id_20121031_00018582) « Monitoring crustal deformation in the Central Andes : Nazca – South America subduction and sub-Andean ranges »
-  Sentinel access : open access, participation top CEOS seismic Pilot where the Andes have been defined as a major interest area, which guarantees a data flow available over the area.

contacts : anne.socquet@ujf-grenoble.fr ; marie-pierre.doin@ujf-grenoble.fr ; ocavalie@geoazur.unice.fr

pour candidater : lien vers le site du CNES, rubrique "Sciences utilisatrices des moyens spatiaux" (SUMS)

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