Current Ground Deformation Along the East Coastal Region of China Derived from GPS Observations (2010-2014)

This study investigated the current ground deformation that occurred along the east coastal region of China. Continuous measurements (2010-2014) from over 100 permanent GPS stations were analyzed. The GIPSY-OASIS software package (V6.3) is employed to obtain single receiver phase-ambiguity-fixed PPP solutions within a global reference frame (IGS08). To determine the magnitude and direction of local ground displacement over time, a Stable East China Reference Frame (SEChinaRF) was established using long-history data from five permanent GPS stations, which are evenly distributed along the China’s east coast and have continuously operated for at least 7 years. The realization of the SEChinaRF is defined in terms of a 14-parameter Helmert transformation from the International GNSS (Global Navigation Satellite System) Reference Frame of 2008 (IGS08). The PPP daily solutions achieved 2-4 mm horizontal accuracy and 7-8 mm vertical accuracy within SEChinaRF. The local reference frame is able to identify ground deformations at the level of 1mm/year. This study indicates that substantial land subsidence has been occurring in the Tianjin area with a steady subsidence rate of up to 45 mm/year during the past four years (2010-2014). The primary driving factor that caused the land subsidence was determined to be the excessive extraction of groundwater. Moderate subsidence (< 1 cm/year) was also observed in the east coastal regions such as Shanghai, Shandong and Guangdong. The GPS stations in eastern China also recorded significant co-seismic and post-seismic displacements induced by the 2011 Tohoku-Oki earthquake (MW 9.0) in Japan. This study indicated that the magnitude and direction of the co-seismic and post-seismic displacement depended on both the distance and azimuth to the earthquake source. The maximum co- and post-seismic (within 3 days after the mainshock) in China was recorded by a station in Changchun, which showed 21 mm horizontal displacement toward southeast. The post-seismic deformation is still occurring in the northeastern China region with a horizontal velocity of approximately 3 mm/year toward the earthquake epicenter. No considerable vertical co- and post-seismic displacements were observed.