Resolve 3-dimensional deformation field in southern California using GNSS and InSAR data

Zheng-Kang Shen, & Zhen Liu

Published August 15, 2021, SCEC Contribution #11473, 2021 SCEC Annual Meeting Poster #100

We have developed a 3D GNSS/InSAR integration algorithm and applied that to a compilation of GNSS and InSAR data in southern California. In the algorithm discrete GNSS data points are interpolated to obtain a 3D continuous velocity field, which is then combined with the InSAR line-of-sight (LOS) velocity data pixel by pixel using the least-squares method. Advantages of our method are: (1) The GNSS data points are optimally interpolated by balancing a trade-off between spatial resolution and solution stability. (2) A new algorithm is developed to estimate realistic uncertainties for the interpolated GNSS velocities, which are used as weights for GNSS data in GNSS-InSAR combination. (3) A Jackknife variance estimation approach is adopted to characterize the uncertainties associated with InSAR deformation map. (4) Each selected track of InSAR data is scaled based on the comparison between the InSAR and GNSS projected LOS values. (5) The ramps and/or offsets of the InSAR data are globally estimated with minimum data misfit.

We applied the approach to GNSS velocities and InSAR data of multiple satellites. For GNSS velocity interpolation, we used continuous GNSS solution produced by the MEaSUREs project. For InSAR LOS velocities, we processed data from multiple satellites (ERS-1,2, Envisat, Sentinel-1, ALOS-2) to derive InSAR time series and LOS velocities, which jointly measure crustal deformation in southern California from 1992-2019. Our result shows that the GNSS and InSAR data are generally consistent for the horizontal velocities at sub-millimeter per year level. The vertical velocity field is determined much better than using GNSS data only, especially for regions experiencing localized deformation. We observe a number of regions (e.g., the Brawley Seismic Zone, Coso Geotherm area, Colorado River Reservation area, Death Valley, Imperial Valley, Los Angeles Basin, Lancaster, Palm Springs, southern Great Basin, San Gabriel Valley, San Diego, Searles Lake, and southernmost Nevada) displaying ~3-8 mm/yr subsidence, possibly resulted from groundwater withdrawal or volcanic deflation. The southern Sierra Nevada is found to uplift at a rate of ~2-4 mm/yr, probably related to droughts. ~1-3 mm/yr uplift is also detected in the southern Anza-Borrego Desert region near the California-Mexico border. We are working on adding more InSAR data to cover the entire southern and partly central California regions, and will report the updated result at the Annual Meeting.

Key Words
GNSS, InSAR, Combination, Southern California

Citation
Shen, Z., & Liu, Z. (2021, 08). Resolve 3-dimensional deformation field in southern California using GNSS and InSAR data. Poster Presentation at 2021 SCEC Annual Meeting.

Related Projects & Working Groups
Tectonic Geodesy