Seasonal driving sources and hydrological-induced secular trend of the vertical displacement in North China

Abstract

Study region: North China (NC) is an important social and economic center in China. Study focus: NC is suffering from obvious land deformation. The vertical time series of 20 Global Positioning System (GPS) stations are explored to determine the seasonal driving sources and hydrological-induced displacement trends together with the mass loading models. A method named SSA-ICA is developed to extract the source signal using singular spectrum analysis (SSA) in conjunction with independent component analysis (ICA). New hydrological insights: The independence of extracted components by SSA-ICA is significantly stronger than that by SSA alone through the mutual information evaluation, and the separation ability of source signals by SSA-ICA is greatly superior to SSA. The good agreements between SSA-ICA-derived independent reconstructed components (IRCs) and mass loading displacements confirm that the atmospheric loading (ATML) and hydrological loading (HYDL) are the primary driving sources of GPS seasonal displacement. Due to the phase biases, we adjust the phases of displacement time series from ATML and HYDL by referring to IRC1 and IRC2, respectively. The average weighted root-mean-squares (WRMS) reduction after phase adjustment is 12.14% higher than that before adjustment, significantly improving the consistency between GPS and mass loading measurements. Moreover, quantitative estimates of the secular displacement trends induced by hydrological mass changes suggest that extensive exploitation of groundwater causes severe land subsidence, especially in the east-central plain.

Keywords

• North China
• SSA-ICA
• Driving sources
• Phase biases
• Groundwater