Using 3-year Sentinel-1 C-band synthetic aperture radar(SAR) data, we observed prominent ground subsidence around the construction site of the Milashan Tunnel, which is on top of the northern SangriCuona Rift(SCR) in southern Tibet. The most deformed area extends ～7 km in the north-south direction and ～6 km in the east-west direction, with a peak subsidence rate of over 10 mm/a in the line of sight direction of both the descending and ascending satellites. Aside from the long-term ground subsidence arising directly from underground water outflow and rock excavation, a regional aseismic fault slip episode is also evident. The aseismic slip event began in May 2016 and ended in July 2016. The surface aseismic displacements can be explained by normal faulting with mainly down-dip movement and a modest right-lateral strike-slip component on a nearly north-south trending fault. The aseismic deformation triggered by the Milashan Tunnel construction demonstrates the sensitive response of crustal-scale tectonics to human activity, which poses high seismic hazards for the heavily populated region.
Global Positioning System data processing is affected by many non-tectonic factors, including the common-mode errors （CME） in station-position time series. The characteristics and origins of CME are still not clear, due to uneven distribution of global GPS networks and the lack of reliable data of the position time series. In this work, data from 241 continuous GPS stations were reprocessed in a consistent way and the results were compared with those generated at Jet Propulsion Laboratory （JPL）. Improvements of residual positions were obtained for many low-quality stations, especially those located in Asia and Australia.
