InSAR and GPS time series analysis in areas with large scale hydrological deformation: separating signal from noise at varying length scales in the San Joaquin Valley

Kyle D. Murray, & Rowena B. Lohman

Published August 15, 2017, SCEC Contribution #7696, 2017 SCEC Annual Meeting Poster #210

Areas of large-scale subsidence are observed over much of the San Joaquin Valley of California due to the extraction of groundwater and hydrocarbons from the subsurface.These signals span regions with spatial extents of up to 100 km and have rates of up to 45 cm/yr or more. InSAR and GPS are complementary observation types that provide important constraints on crustal deformation models and aid our understanding of the relationship between subsurface fluid extraction and seismicity. However, current standard methods for generating InSAR-based displacement time series are suboptimal for the deformation observed in areas like the San Joaquin Valley because (1) the ground surface properties are constantly changing due largely to agricultural activity, resulting in low coherence in half or more of a SAR frame, and (2) the deformation signals are distributed throughout the SAR frames, and are comparable to the size of the frames themselves. Therefore, referencing areas of deformation to non-deforming areas and correcting for long wavelength signals (e.g. atmospheric delays, orbital errors) is particularly difficult.

We address these challenges by exploiting pixels that are stable in space and time, and use them for weighted spatial averaging and selective filtering before unwrapping. We then compare a range of methods for both long wavelength corrections and referencing via automatic partitioning of non-deforming areas, then benchmark results against continuous GPS measurements. Our final time series consists of nearly 15 years of displacement measurements from continuous GPS data, and Envisat, ALOS-1, Sentinel SAR data, and show significant temporal and spatial variations. We find that the choice of reference and long wavelength corrections can bias long-term rate and seasonal amplitude estimates, introducing variations of as much as 100% of the mean estimate. As we enter an era with free and open data access and regular observations plans from missions such as NISAR and the Sentinel constellation, our approach will help users evaluate the significance of observed deformation at a range of spatial scales and in areas with challenging surface properties.

Citation
Murray, K. D., & Lohman, R. B. (2017, 08). InSAR and GPS time series analysis in areas with large scale hydrological deformation: separating signal from noise at varying length scales in the San Joaquin Valley. Poster Presentation at 2017 SCEC Annual Meeting.

Related Projects & Working Groups
Stress and Deformation Over Time (SDOT)