A Field of Annual Accumulation of Strain Energy Density and its Tectonic Activity in North China by GPS Measurements

Global Positioning System (GPS) observations from three measurement campaigns from 1995 to 1999 are used in a study of the tectonic activity and earthquake hazards in North China. These GPS data were firstly processed together with about 13 Global IGS stations using the GAMIT software to get the baseline solutions, then crustal horizontal motion in ITRF97 frame and with respect to Eurasia were obtained based on these baseline solutions and their variance-covariance matrix using the GPS network adjustment software PowerADJ developed by Wuhan University. Using the GPS velocity field we estimate the annual accumulation of strain rate field and annual accumulation of density of strain energy field. These resulting fields show the following: (1) most stations move at a rate of (3–12 mm/a)±3.4mm/a east-southeastwards with respect to Eurasia. (2) Tangshan-Hejian-Xingtai is an active seismotectonic compression border. Datong-Taiyuan is an active extension border with slight dextral rotation. (3) Beijing–Tianjin–Bohai Bay region and Xingtai region are of higher shear strain rate than other regions. Zhangjiakou–Beijing–Tianjin–Bohai Bay region and Jinan region are of much higher annual accumulation of strain energy density than other regions in North China, these regions are of higher amount of the energy storage. The Bohai Bay region is also located in a transition zone from positive to negative surface strain rate, it may be a region of earthquake risk in the future.