The effect of large reservoirs impoundment to the spatial and temporal variations of regional crustal deformation in Hubei Province, China

The total capacity of Three Gorges Reservoir (TGR) and Danjiangkou Reservoir (DJR) is large and has significant seasonal fluctuations, which give rise to crustal instability. In this research, we focus on studying the temporal and spatial variation of crustal deformation in Hubei Province caused by reservoir impoundment of TGR and DJR. The Digital Elevation Model, historical hydrological information, GPS monitoring data and load-induced deformation model are combined to monitor the crustal deformation. The modeled results indicate that in the trapezoidal area between the TGR and DJR, the average vertical deformations at different latitudes have different variation tendencies. The vertical deformation modulus and fluctuation amplitude are larger at the latitude of 33°N/32.5°N from 2003 to 2006 and at the latitude of 31°N/32.5°N from 2008 to 2014, while the latter are much larger than the former. Moreover, from 2008 to 2014, the frequency and the intensity of seismic activities are all enhanced significantly in this region. The modeled results at the GPS sites are consistent with the vertical displacement of GPS monitoring results in trends and the waveform. It can be inferred that the seasonal deformation is elastic. The horizontal deformation components have the same variation trends with that at each GPS monitoring station, which demonstrates that the whole region is moving toward the southeast. The spatial variation of crustal deformation demonstrates that the impoundment of TGR in 2003 causes significant vertical displacements, with the maximum modulus of 32 mm downward located in Xiangjiang River's estuary. When the water storage increases, the maximum value will become larger, and the location will move toward the upstream. Besides, the earthquakes occurred more frequently in the region with maximum deformation modulus.