Mapping Active Surface Deformation in Fusagasugá and Silvania, Colombia, Using Sentinel-1 SBAS-InSAR and Campaign GNSS Observations

The municipalities of Fusagasugá and Silvania in Cundinamarca, Colombia, include rural mountainous terrain and infrastructure exposed to hydrometeorological and geological hazards, yet spatially continuous ground-deformation measurements remain limited. We mapped surface deformation using ascending and descending Sentinel-1 Small Baseline Subset Interferometric Synthetic Aperture Radar (SBAS-InSAR) observations acquired during 2020–2021 and compared local InSAR time series with four-epoch campaign GNSS measurements at four sites. The InSAR analysis identifies spatially coherent line-of-sight (LOS) deformation in San Antonio, San Luis Bajo, and El Bermejal. At P2 in San Antonio, the full-period linear trends of the coherence-weighted local InSAR time series are +4.7 mm/year for the ascending geometry and −17.8 mm/year for the descending geometry; descending LOS velocities reach approximately −31 mm/year at El Bermejal. At San Antonio, inversion of paired ascending and descending LOS velocities, assuming negligible north–south motion, yields dE=−18.3 mm/year (18.3 mm/year westward) and dU=−8.4 mm/year (8.4 mm/year downward). GNSS-to-LOS comparisons show substantial discrepancies at P2 and P4 and inconclusive agreement at P3; campaign GNSS is therefore treated as complementary point-scale evidence rather than as independent validation of the InSAR time series. The resulting deformation maps provide a screening basis for prioritizing follow-up geodetic, geomorphological, and geotechnical investigations rather than constituting landslide-susceptibility, hazard, risk, or early-warning products.