Integrating Community Research into a Consensus Geodetic Model: A Community Velocity Field Exercise for the SCEC Community Geodetic Model (CGM)

Ekaterina Tymofyeyeva, Michael Floyd, Kathryn Materna, Zhen Liu, Zheng-Kang Shen, Gareth J. Funning, Molly Zebker, Eric J. Fielding, Mradula Vashishtha, & William E. Holt

Submitted August 30, 2026, SCEC Contribution #15588, 2026 SCEC Annual Meeting Poster #TBD

The SCEC Community Geodetic Model (CGM) is a unified representation of crustal deformation across California, integrating GNSS and InSAR observations to constrain interseismic strain accumulation, fault slip rates, and other deformation processes. As the diversity, density, and temporal span of contributed geodetic data and models have grown — spanning multi-track Sentinel-1, ALOS-2, OPERA DISP, NISAR, GNSS, and multiple published statewide velocity and strain-rate fields — the central challenge has shifted from producing any single model to rigorously comparing and subsequently integrating many models, establishing best-practice algorithms and approaches. Contributed models encode different assumptions, reference frames, uncertainty treatments, and spatial-temporal sampling, and cannot be meaningfully understood or fused without a coordinated community exercise.

We present the starting point for a new SCEC Technical Activity Group (TAG) that will address this gap through a Community Velocity Field Exercise: a structured intercomparison of contributed statewide velocity and strain-rate fields over California, followed by prototyping of a reproducible framework for integrating those inputs into a single consensus 3-D CGM. We describe the proposed contribution template (common statewide grid; standardized metadata for reference frame, time window, transient handling, and uncertainty definitions), the quantitative comparison metrics (RMS difference maps, per-region statistics over creeping segments, basins, and fault zones), and two integration paths — classical inverse-variance-weighted combination and hierarchical Bayesian approaches with explicit uncertainty propagation — that will be benchmarked against each other during the exercise.

We introduce the candidate contributed models identified so far, including the Shen and Liu (2025) InSAR/GNSS combination, SIO/UCSD products (e.g., Xu et al., 2021; Lindsey et al., 2014), UCR InSAR (Lin and Funning, 2017), the Holt et al. / Kim et al. (2026) strain-rate field, CGM v2.0.0. We look forward to incorporating additional models from groups outside of this TAG. The poster outlines the one-year workplan and quarterly milestones, and describes coordination with parallel TAGs. We invite feedback from the SCEC community on the exercise design, model integration techniques, and comparison metrics, and welcome additional groups interested in contributing statewide velocity or strain-rate fields to future iterations.

Key Words
Community Geodetic Model

Citation
Tymofyeyeva, E., Floyd, M., Materna, K., Liu, Z., Shen, Z., Funning, G. J., Zebker, M., Fielding, E. J., Vashishtha, M., & Holt, W. E. (2026, 08). Integrating Community Research into a Consensus Geodetic Model: A Community Velocity Field Exercise for the SCEC Community Geodetic Model (CGM). Poster Presentation at 2026 SCEC Annual Meeting.

Related Projects & Working Groups
Community Earth Models (CEM)