| Authors: |
Mariana ENEVA, David ADAMS, Giacomo FALORNI, Jessica MORGAN |
| Keywords: |
satellite radar interferometry, InSAR, PSInSAR, SqueeSAR, subsidence, surface deformation, geothermal, Imperial Valley, Salton Trough, Hudson Ranch, Salton Sea geothermal field, Heber, East Mesa, Brawley, San Andreas fault, Imperial fault, Superstition Hi |
| Conference: |
Stanford Geothermal Workshop |
Session: |
Geophysics |
| Year: |
2013 |
Language: |
English |
| Geo Location: |
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| Abstract: |
The InSAR (interferometric synthetic aperture radar) approach is being used in Imperial Valley of southern California to detect and characterize the surface deformation in existing geothermal fields, possible future geothermal developments, and around faults in their vicinities. The data are from the Envisat satellite, collected over the period 2003-2010. The specific InSAR technique used is SqueeSARTM, developed at TRE. It identifies permanent and distributed scatterers (PS and DS), which play the role of numerous benchmarks throughout the study area. Deformation time series are obtained at all individual scatterer locations and are used to estimate annual deformation rates. The technique is particularly suitable for vegetated and rural areas, thus providing unprecedented results for the agricultural lands of Imperial Valley, where conventional InSAR methods have not worked before. Significant subsidence is observed within two bowls on the territory of the CalEnergy units of the Salton Sea geothermal filed. Distinct, although lesser subsidence, is also seen around the new Hudson Ranch development nearby (Energy Source, LLC), for which the satellite data (2003-2010) are from pre-production times. Subsidence is seen at East Mesa and Heber as well, with the latter field also displaying uplift in some parts. The InSAR results are compared with annual leveling data collected at the CalEnergy units of the Salton Sea geothermal field and at Heber. In addition, it has been observed that differential movements clearly mark both sides of Superstition Hills and Imperial faults, as well as the southern portion of the San Andreas. These surface displacements are attributed to the ongoing regional extension due to the relative movements of the North American and Pacific plates, as well as to localized tectonic deformation associated with fault networks, pull-apart basins, and rotational blocks. In some cases (e.g., East Mesa) the geothermal activities also significantly contribute to the observed surface movements. InSAR thus provides unprecedented information on surface deformation in Imperial Valley, as long as a suitable technique, such as SqueeSARTM, is used to tease out signals despite the presence of extensive agriculture. No ground-based measurements can provide the spatial and temporal detail achieved in this analysis. Such observations can be effectively used for pre-production reservoir assessment, for feedback to mitigate any environmental impact that might occur at existing fields, and for ongoing exploration to help identify suitable drilling targets. |
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