A study on annual accumulation of strain energy density significance by using GPS measurements in North China

Global Positioning System (GPS) data in three measurement campaigns from 1995 to 1999 are used to study tectonic activity and earthquake hazards in North China. These GPS data were firstly processed together with the data from 13 Global IGS stations using the GAMIT software to get the baseline solutions. Then GPS velocity field in north China with respect to Eurasia was obtained in ITRF97 frame based on these baseline solutions and their variance-covariance matrix using the GPS network adjustment software Power ADJ developed by Wuhan University. Using the GPS velocity field, we estimate the annual accumulations of strain rate field and strain energy density field. These fields show that (1) Most stations move eastward or southeastward at a rate of (3-12mm/a) ± 3.4mm/a with respect to Eurasia. (2) Tangshan-Hejian-Xingtai is an active seismotectonic compression border. Datong-Taiyuan is an active extension border with slight dextral rotational; (3) Beijing-Tianjing-Bohai and Xingtai regions are higher shear-strain-rate region. Zhangjiakou-Beijing-Tianjin-Bohai and Jinan regions exhibite higher annual accumulation of strain energy density than other regions in North China, showing more amount of the energy storage. The Bohai region is also located in exchanging zone for positive to negative surface strain rate, it maybe the earthquake risk region in the future.