Quantifying the effect of non-seasonal non-tidal loadings on background noise properties of GPS vertical displacements in mainland China

Abstract

Global positioning system (GPS) vertical displacements measuring the elastic response of Earth’s crust to tectonic motion have been used to produce vertical velocity estimates. These accurate estimates require minimal contamination by non-tectonic deformations, mainly including atmospheric-oceanic-hydrologic mass loadings. However, the variability of background noise properties in GPS time-series caused by the removal of these loading deformations remains unclear. In this study, we investigate how the non-seasonal parts of two types of combined non-tidal loading deformations (i.e., atmospheric plus non-tidal oceanic loadings (AO) or AO plus hydrological loadings (AOH)) affect the background noise properties. The study region is focused on the mainland China, and the data are 258 GPS vertical land motion time-series from the Crustal Movement Observation Network of China (CMONOC). Before and after the loading correction, we found that the more satisfactory background noise model is white plus power-law noise. The AO correction achieves significant improvement in white noise estimates and drastically reduces power-law noise content. Meanwhile, the estimated spectral index shows the worse stationarity of background noise properties but can be alleviated by additional hydrological loading correction. Besides, the exploited GPS imaging method reveals the spatial heterogeneity of the background noise amplitude, spectral index, and velocity uncertainty.