InSAR Analysis of the 2006 Slow Slip Event in the Guerrero-Oaxaca Zone using NARR
Abstract
Aseismic slip, called Slow Slip Event (SSE), have been observed in the last decade by GPS in subduction zones. The SSE occurring in the Guerrero-Oaxaca Mexican subduction zone are among the largest recorded SSE in the world. They are monitored by 14 permanent GPS stations located in along a N-S transects between Mexico city and Acapulco and another E-W transect along the coast. This network allowed to detect recurrent transient motions, observed about each four years since 1998. This result bring new constrains about subduction dynamic and the seismic gap segment observed on the subduction zones. Nonetheless, improving the coverage of geodetic measurement in this area is essential to better determine the spatial distribution of the slip and, then, the released energy during these events. SAR interferometry (InSAR) has the potential to increase spatial density of geodetic measurements. However detecting SSE by InSAR remains a challenge because the related ground deformations are distributed over long distance (hundreds of km) with small gradient and, in the Guerrero zone, crossing zones of low phase coherence. Here, we present a new approach to improve INSAR measurement of such events with application on an SSE that occurred between April 2006 and December 2006, because it is the best documented event by GPS in the area and because ESA archive radar images covers this event. We investigate ENVISAT images along four descending tracks and two ascending tracks crossing the Guerrero zone. We first process interferograms along the descending track 255 (about 500 km × 100 km) covering the permanent GPS network. We compute 32 interferograms based on 12 Envisat images acquired between November 2004 and March 2007. Starting from the topography-corrected interferograms, the first step aims to correct them from atmospheric perturbations, which are the main limiting factor. Among these perturbations, one can distinguish the tropostatic delay, due to troposphere stratification, usually considered as constant at the frame scale (100 km × 100 km) and delays induced by the turbulent phenomena in atmosphere. Our approach focuses on the correction for tropostatic delay that induced a correlation between phase and elevation. For that purpose, we use NARR (North American Regional Reanalysis), a meteorological model of re-analysis of atmospheric data. This model allows us to calculate the tropostatic delay on a grid with nodes separation of 32km. This correction is an important issue, not only to decrease the atmospheric phase screen, but also to reduce the phase variance and then to help to unwrap the phase. We show that NARR provides a good estimation of the tropostatic delay whose variations are of the same order of magnitude that the amplitude of the delay (10-3 rad/m) between Mexico and the coast. To complete the analysis, a correction of the interferograms for interseismic signal occurring before April 2006 and after December 2006 is needed. Finally, a stacking of the corrected interferogram is performed in order to reduce turbulent atmospheric perturbation.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.G51A0602C
- Keywords:
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- 1200 GEODESY AND GRAVITY;
- 1207 Transient deformation (6924;
- 7230;
- 7240);
- 1209 Tectonic deformation (6924);
- 1220 Atmosphere monitoring with geodetic techniques (6952);
- 1294 Instruments and techniques