Spatial heterogeneity of nonlinear signals, background noise and vertical velocities in GNSS vertical time series across the Tibetan Plateau: A systematic analysis of multi-source loading corrections

Summary This study quantifies the spatial heterogeneity of nonlinear signals, background noise, and vertical velocities in GNSS vertical time series across the Tibetan Plateau (TP), using multi-source loading corrections to isolate tectonic deformation. We analyzed 20 years of GNSS data (2002–2021) from CMONOC and NGL networks, processed via GipsyX and referenced to ITRF2014. Non-tidal atmospheric (NTAL), oceanic (NTOL), and hydrological (HYDL) loading effects were applied utilizing operational models from GFZ and GRACE mascon data (CSR/JPL/GSFC), followed by common mode error (CME) filtering. The findings highlight significant spatial heterogeneity: Monsoon-dominated southern TP exhibits 10–20 per cent RMS reduction after non-tidal atmospheric-oceanic (AO) loading corrections, while northern TP shows minimal improvement (<10 per cent), highlighting non-atmospheric noise dominance. Integration of AO and GRACE-modeled hydrological (AOG) loading corrections outperform soil moisture-based models (AOH), achieving 25–35 per cent RMS reduction in glacier-covered Himalayas by resolving cryospheric mass loss. Spectral and principal component analysis (PCA) analyses confirm AOG’s superiority in suppressing interannual signals (PC1 variance: 62.7 per cent vs. AOH’s 60.3 per cent), particularly in monsoon-ENSO-affected regions. Noise modeling demonstrates high spatiotemporal correlations (63.1 per cent WN + FN in raw data), with flicker noise (FN > 5.2 mm) linked to seismic activity in southeastern TP and power-law noise (PL > 3.5 mm) to permafrost dynamics in the north. Post-AOG_CME processing simplifies noise structures (WN + GGM dominance: 32.9 per cent), reducing velocity uncertainties by 26.9 per cent and revealing a residual + 1.2 mm/yr uplift in the southern inner TP, indicative of mid-crustal flow. Persistent uncertainties (>0.55 mm/yr) along the Himalayan thrust front correlate with deep lithospheric boundaries. Our findings demonstrate the necessity of integrating GRACE-derived corrections with CME filtering to accurately delineate tectonic signals within the intricate suture zones of the TP, offering crucial insights into plateau-wide geodynamic processes.