Detection of Nonlinear Slow Deformation From Wrapped Phase Gradients in Low-Coherence Terrain
Zhen Li, & Jean-Philippe AvouacSubmitted August 30, 2026, SCEC Contribution #15382, 2026 SCEC Annual Meeting Poster #062
The temporal evolution of slow deformation reflects the redistribution of crustal stress and mass under tectonic and anthropogenic forcing and provides constraints on the driving processes. Quantifying this evolution requires sustained observations, yet decorrelation in vegetated terrain often prevents reliable phase unwrapping and limits conventional InSAR time series. A phase gradient, the wrapped phase difference between neighboring pixels, retains local deformation without unwrapping interferograms while suppressing atmospheric delays. Network-based phase-gradient stacking (NPG-Stacking; Xu and Wang, 2025) exploits this observable in low-coherence terrain, but temporal stacking reduces deformation to a mean rate or imposed temporal model and cannot resolve nonlinear behavior.
Here we combine adaptive phase linking over statistically homogeneous pixels with gradient-domain inversion. Phase linking estimates common-reference phases over distributed scatterers, enabling reconstruction of arbitrary interferograms and explicit network design. We estimate displacement at each epoch from wrapped spatial gradients. We prove that spatial differencing and temporal inversion commute, and derive an a priori criterion that determines whether network baselines allow unambiguous recovery of deformation.
We test the method using five C-band Sentinel-1 datasets. In forested Shikoku, velocities agree with GNSS at 97 stations with a 2.18 mm/yr discrepancy and resolve strike slip across the Median Tectonic Line. Far-field postseismic velocities following the 11 March 2011 Mw 9.0 Tohoku-Oki earthquake reach 3.4 mm/yr and agree with observations at 72 GEONET stations. The recovered time series resolves an acceleration in Delaware Basin subsidence at level of cm/yr, while two viewing geometries at Kumamoto distinguish decaying afterslip from persistent viscoelastic relaxation. Where the criterion is satisfied, results agree with GNSS. Together, these results make nonlinear crustal deformation quantitatively observable in terrain where C-band InSAR has yielded little usable signal, revealing its evolution under tectonic processes and industrial fluid operations.
Citation
Li, Z., & Avouac, J. (2026, 08). Detection of Nonlinear Slow Deformation From Wrapped Phase Gradients in Low-Coherence Terrain. Poster Presentation at 2026 SCEC Annual Meeting.
Related Projects & Working Groups
Tectonic Geodesy
