Southern California 3-D Velocity and Strain Rate Field from Joint Inversion of GNSS and InSAR Data

Mradula Vashishtha, Jeonghyeop Kim, & William E. Holt

Submitted September 8, 2024, SCEC Contribution #13921, 2024 SCEC Annual Meeting Poster #078

Southern California exhibits complex deformation patterns and fault systems. We combine the strengths of GNSS and InSAR using the joint inversion to overcome their spatial and directional limitations respectively.

We employ a physics-based approach based on solutions of the force balance equations on a sphere using the weak formulation in finite elements. We obtain basis function responses to force couples phi_phi, theta_theta, phi_theta in the horizontal and for Ur/r for the vertical basis function response. For the spherical case the vertical response is weakly coupled to the horizontal. Basis functions provide the response in vertical and horizontal velocity, the horizontal strain rates and rotation rates about the vertical axis. Solutions can also be expressed in terms of the input force couples, which are the vertical derivative of horizontal shear stress (VDoHS).

The joint inversion aims at finding the best-fit linear combination of horizontal and vertical basis functions that can predict the input horizontal GNSS and ascending and descending InSAR data. We obtain the InSAR data from Xu et al. 2021 and GNSS data from MIDAS (Blewitt et al. 2016) and Yuehua et al. 2023. We then apply a damped weighted least squares problem solved using Ridge regularization and Akaike Bayesian Information Criterion.

We present the interseismic kinematic solution for Southern California. The joint inversion yields a high resolution 3-D velocity field and strain rate field prediction throughout Southern California. We also obtain high resolution predictions of the patterns of VDoHS throughout southern California. The patterns and magnitudes of strain rates and VDoHS will enable us to determine the locking depth and slip rates on the major strike slip and dip slip structures. Moreover, the vertical velocity field shows strong correlations with groundwater changes in basins, having both natural and anthropogenic sources for the changes.

Key Words
Community Earth Models (CEM), Stress and Deformation Over Time (SDOT), Tectonic Geodesy, GNSS, InSAR

Citation
Vashishtha, M., Kim, J., & Holt, W. E. (2024, 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.

Related Projects & Working Groups
Tectonic Geodesy