Results of the Crustal Deformation by GPS Survey and Horizontal Strain Rate Fields in the Three Gorges Area

Bernese GPS Software 4.2 is used to analyze GPS data from six repeated surveys occupied by the GPS network of the Three Gorges Reservoir Induced Earthquake Monitoring System from 1998 to 2003.The result shows that the crustal deformation in the Three Gorges Reservoir area is less active with a marginally measurable rate of 0 and 3mm/a(±0.1~±2.0mm/a)with respect to stable South China. Whereas, The vertical subsidence is about 10mm to 35mm alongshore after impoundment.We have simulated present-day GPS velocity solution with a bi-cubic spline interpolation function to estimate the horizontal strain rate fields before impoundment.The result shows that the tectonic deformation background of the Three Gorges area is slight (the horizontal strain rate is about 10^-9/a to 10^-10/a).