A quantitative research for present-time crustal motion in Fujian Province, China and its marginal sea

Based on the Chinese mainland GPS network (1994–1996), Fujian GPS network (1995–1997), cross fault deformation network (1982–1998), precise leveling network (1973–1980) and focal mechanism solutions of the recent several tens years, we synthetically and quantitatively studied the present-time crustal motion of the southeast coast of Chinese mainland—Fujian and its marginal sea. We find that this area with its mainland together moves toward SE with a rather constant velocity of 11.2±3.0 mm/a. At the same time, there is a motion from the Quanzhou bay pointing to hinterland, with a major orientation of NW, extending toward two sides, and with an average velocity of 3.0±2.6 mm/a. The faults orienting NE show compressing motions, and the ones orienting NW show extending motions. The present-time strain field derived from crustal deformation is consistent with seismic stress field derived from the focal mechanism solutions and the tectonic stress field derived from geology data. The principal stress of compression orients NW (NWW)—SE (SEE). Demarcated by the NW orienting faults of the Quanzhou bay and Jinjiang—Yongan, the crustal motions show regional characteristics: the southwest of Fujian and the boundary of Fujian and Guangdong are areas of rising, the northeast of Fujian are areas of sinking. The horizontal strain rate and the fault motion of the former are both greater than the later. The side-transferring motion of Hymalaya collision zone and the compression of the west pacific subduction zone affect the motion of the research area. The amount of motion affected by the former is larger than the later, but the former is homogeneous and the later is not, which indicates that the events of strong earthquakes in this region relate more directly with western pacific subduction zone.