Objectives North China is an important social and economic area in China but suffers from severe surface deformation. Monitoring the surface displacement effectively and timely can provide data basis for understanding the deformation mechanism and predicting disasters. However, the surface vertical displacement in North China shows significant seasonal fluctuations. Hence, this paper aims to analyze the spatiotemporal feature of seasonal vertical displacement and determine the driving sources.
Methods Firstly, the vertical time series of 20 global navigation satellite system (GNSS) stations from January 2011 to November 2019 are decomposed by independent component analysis. Secondly, the first six independent components (ICs) are derived and compared with the vertical displacements caused by environmental loadings.
Results The results show that GNSS-IC1 presents obvious annual variation, as well as a relative uniform spatial response, which is highly consistent with the displacement time series derived from atmospheric loading, and the average correlation coefficient at all stations is 0.60. GNSS-IC2 and GNSS-IC3 are both the mixed signals constrained by annual and intra-annual periods, while the spatial responses reflect locally clustered characteristics, which corresponds to the distribution of water resources in North China. After combining GNSS-IC2 and GNSS-IC3 as GNSS-IC2/3, the average correlation coefficient between GNSS-IC2/3 and the hydrological loading displacement time series at all stations is 0.50.
Conclusions The temporal component of each IC is generally less clustered by different time cycles and the spatial response shows distinct localized characteristics. Atmospheric and hydrological loadings are the primary driving sources of seasonal vertical displacement in North China. However, the seasonal displacements induced by other effects, including non-tide ocean loading and thermal expansion effect of bedrock and observation pillar, are not extracted and need further analysis.