Transient deformation during the Milashan Tunnel construction in northern Sangri-Cuona Rift, southern Tibet, China observed by Sentinel-1 satellites.

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 Sangri-Cuona 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.