SCEC Award Number 22083 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title GNSS and InSAR Integration for 3-D Deformation Field and Time Series in California
Investigator(s)
Name Organization
Zheng-Kang Shen University of California, Los Angeles Zhen Liu National Aeronautics and Space Administration
Other Participants
SCEC Priorities 1a, 2a, 3e SCEC Groups Geodesy, SDOT, CXM
Report Due Date 03/15/2023 Date Report Submitted 03/25/2023
Project Abstract
 We have developed an algorithm to integrate GNSS and InSAR data for a 3-dimensional crustal deformation field at the Earth’s surface. In the algorithm discrete GNSS data points are interpolated to obtain a 3-dimensional continuous velocity field, which is combined with InSAR line-of-sight velocity data pixel-by-pixel using the least-squares method. Application of this method to California and western Nevada shows its capability of successfully restoring 3-dimensional continuous deformation field. Our result shows that the GNSS and InSAR data are generally consistent for the horizontal velocities at about 1 mm/yr or sub-mm/yr level. The vertical velocity field is determined with much more details than using GNSS data only, especially for regions experiencing localized tectonic/hydrological/anthropogenic deformation. Widespread subsidence is detected in the Central Valley and Sacramento Valley due to water withdrawal, reaching ~180 mm/yr in the southern Central Valley. Other regions with noticeable vertical deformation include the Los Angeles basin, Lancaster, and Imperial Valley, where hydrologic and/or volcanic processes caused subsidence up to 3-10 mm/yr. The San Francisco Bay area between the San Andreas-Sargent and Hayward fault is found uplifting at a rate up to 5 mm/yr, and the strict confinement of the uplift motion by the two fault systems suggests fault controlled vertical deformation. Strong uplift (up to 10 mm/yr) is also detected in the Southern Coastal Ranges between the Kettleman Hills-Lost Hills thrust and the San Andreas fault, possibly due to elastic response caused by drought and water withdrawal in the Central Valley.
Intellectual Merit Our project contributes directly to advancing two SCEC research objectives described in 4.2 Tectonic geodesy of SCEC2022RFP: 1) “Developing a Community Geodetic Model (CGM) for use by the SCEC community in system-level analyses of earthquake processes over the full range of length and timescales”, and 2) “Developing methods to integrate and update these dense spatio-temporal datasets” (i.e. GNSS and InSAR). The 3-D velocity field we have developed for California and western Nevada provides an essential dataset in studying physical processes of tectonic, hydrological, and anthropogenic activities and earthquake hazards for the region. A unified and well-constrained 3-D deformation field that combines the complementary strength of InSAR and GNSS datasets will be part of the key product of the CGM group to support the SCEC’s mission for such studies. The method we have developed for GNSS/InSAR data combination is creative, and the approach of optimal estimation of the GNSS data errors is original. Detailed 3-D deformation field we have obtained has revealed abundant deformation patterns not known before and in much detail, particularly in vertical direction. They include, for example: a) severe and widespread subsidence in Central Valley and Sacramento Valley, b) fault controlled uplift in the San Francisco Bay area, and c) fault controlled and drought related uplift in the central Coastal Ranges. These features will be incorporated in the SCEC consensus GNSS/InSAR integrated CGM model.
Broader Impacts Results of this project have been shown as a poster at the 2022 SCEC annual meetings, and discussed with colleagues of SCEC Tectonic Group. Shen has processed campaign GPS data observed in California to derive station velocities and coseismic and postseismic displacements, and contributed the solution to the SCEC CGM project. He has also participated workshops organized by the Tectonic Group of SCEC for coordination of the CGM project. Liu has been actively participating and contributing to the development of SCEC CGM InSAR consensus model. These include providing independently processed and analyzed InSAR velocities and displacement time series as one input model for deriving CGM InSAR consensus model, participating bi-weekly CGM InSAR group discussion, contributing to product cal/val and uncertainty comparison, benchmark test and outreach effort etc. The first CGM model viewer has been developed for broader community engagement as part of the effort. The group has made the provisional version of the CGM-viewer available for the community comment and feedback (http://moho.scec.org/cgm-viewer/).
Exemplary Figure Figure 4. Combined GNSS and InSAR 3-D velocity field. A and B are amplitudes of the horizontal and vertical components, respectively. White frames in B enclose significant subsidence regions within which the GNSS vertical data are not used for SAR orbital ramp estimation. Note that the subsidence rate in southern part of Central Valley is much higher but capped in color scale. C, D, and E are perpendicular, tangential, and vertical velocity components along profiles shown in A. Red squares are the GNSS data, and light-pink and blue lines are the combined solutions with and without accounting for fault creep effect, respectively. The pink lines on the San Andreas fault mark the creep sections along the fault.

Credit: Shen, Z-K, and Z. Liu, GNSS and InSAR Integration for 3-D Deformation Field and Time Series in California, 2022 SCEC Report.
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