SCEC Award Number 24177 View PDF
Proposal Category Individual Research Project (Single Investigator / Institution)
Proposal Title A Statewide California 3-D Velocity and Strain Rate Field from Joint Inversion of GNSS and InSAR Data
Investigator(s)
Name Organization
William Holt Stony Brook University Mradula Vashishtha Stony Brook University
SCEC Milestones A3-3, A3-5, A3-6 SCEC Groups CEM, Geodesy, SDOT
Report Due Date 03/15/2025 Date Report Submitted 03/16/2025
Project Abstract
 We develop a joint inversion algorithm for continuous surface 3-D velocities and associated horizontal strain rate fields. We employ a physics-based approach based on solutions of the force balance equations on a sphere using the weak formulation in finite elements. The goal of this inversion is to find the best-fit linear combination of these basis functions that predict both GNSS and InSAR measurements. We then apply a damped weighted least squares inversion using Ridge regularization and Akaike Bayesian Information Criterion. We present the interseismic kinematic solution for Statewide California. The joint inversion yields a high resolution 3-D velocity field and strain rate field prediction throughout California. We also obtain high resolution predictions of the patterns of the vertical derivative of horizontal shear stress (VDoHS) rates throughout California. The patterns and magnitudes of strain rates and VDoHS rates enable us to determine the locking depth and slip rates on San Jacinto Fault and the southern part of San Andreas. Moreover, the vertical velocity field shows strong correlations with groundwater changes in basins, having both natural and anthropogenic sources for the changes.
SCEC Community Models Used Community Geodetic Model (CGM), Community Stress Model (CSM)
Usage Description The community fault model was used to infer expected fault strike. The force rates (VDoHS) were projected onto these expected strike directions to enable estimates of force rate peak widths perpendicular to the faults. These fault strike directions were also used to rotate the strain rate tensor to get peak shear strain rate magnitudes and widths across the faults. The shear strain rate and force rate peak magnitudes and peak widths are used to infer fault locking depths and fault slip rates.
Intellectual Merit We have calculated a statewide California estimate of the time-averaged 3-D velocity field, strain rate field, rotation rates, and VDoHS rates. We have also calculated the locking depth and slip rates of southern San Andreas and San Jacinto Faults. The VDoHS rates have helped us gain new insights on SCEC Earth System Science Goal “(i) understanding the distribution of forces that load the fault network”. Our work is an ongoing effort to achieve SCEC Milestones A3-6, A3-5 and A3-3.
Broader Impacts Our goal is to contribute our final Statewide California model products, together with the algorithm, to the SCEC CGM. We also plan to participate in the Community Velocity Model exercise (SCEC Proposal 25203) to do a comparative study with other groups working on different methods for jointly inverting GNSS and InSAR archived in the CGM. This funding supported PhD student Mradula Vashishtha who presented results at both SCEC annual meeting in September 2024 and also at the AGU meeting in Washington DC in December 2024.
Project Participants PhD student Mradula Vashishtha, Stony Brook University.
Exemplary Figure Figure 5d. Shear component of the vertical derivative of horizontal stress (VDoHS) rates (vector field) obtained from the Joint Inversion of GNSS and InSAR data. The underlying field of shear strain rates is color contoured. The VDoHS, together with shear strain rates, can be used to derive the locking depth and slip rates on major faults.
Credit: Vashishtha, M., Kim, J., & Holt, W. E. (2024a, 09). Southern California 3-D Velocity and Strain Rate Field from Joint Inversion of GNSS and InSAR Data. Poster Presentation at 2024 SCEC Annual Meeting. SCEC Contribution 13921
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