Time series analysis of ERS and ENVISAT InSAR data in Northern Mojave, California
Abstract
The Garlock fault is the only major left-lateral fault in Southern California and is viewed as a conjugate structure with respect to faults in the San Andreas system and the Eastern California Shear Zone (ECSZ). Previous results obtained with InSAR data analysis suggest that during the 1992-2000 decade, a prominent fault system in the ECSZ (the Blackwater - Little Lake fault system) accommodated strain at a rate exceeding its long-term (geologic) rate by a factor of at least 3. During the same period, the study also suggests that the Garlock fault accumulated strain at a slower rate than its geological rate, or even not at all in its eastern section. This intriguing observation raised a number of questions about the temporal behavior of faults in the northern Mojave and stress transfer between near-by structures. With an InSAR archive of almost 18 years, we revisit the northern Mojave Desert faults area to determine whether the rapid strain accumulation observed between 1992 and 2000 is actually occurring at a steady rate or whether its rate varies over the 1992-2000 time period. Because of the small magnitude of the signal, a careful treatment of errors due to atmospheric phase delay must be undertaken. We use the newly released North America Regional Reanalysis (NARR) global atmospheric model distributed by NOAA to estimate the radar phase delay produced by the stratified atmosphere. For each epoch of radar acquisition, a vertical profile of the air index of refraction is computed at each of the NARR grid nodes. The phase delay at each image pixel is then estimated by interpolation within the NARR grid and integration along the atmospheric column above the elevation of the pixel. A comparison between the model-derived and InSAR observed phase-topography dependence shows that, for Southern California, global models provide an effective way of correcting phase delay signal due to the stratified troposphere. The complete ERS/ENVISAT archive is processed and corrected using the approach above. Preliminary comparison of ERS and ENVISAT data seems to indicate that the transient rate observed during the 1992-2000 (ERS) period is slowing down during the following decade covered by ENVISAT data. This may suggest that the fast strain rate observed using the ERS data was a post-seismic process subsequent to the Landers, 1992 event.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.G42A..06P
- Keywords:
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- 1209 GEODESY AND GRAVITY / Tectonic deformation;
- 1242 GEODESY AND GRAVITY / Seismic cycle related deformations;
- 7230 SEISMOLOGY / Seismicity and tectonics