Preliminary Study of Block Rotation in North China Area Using GPS Measurements

Repeated GPS surveys in North China provide a direct measurement of current crustal motions. GPS surveys have been carried out in this region in 1992, 1995, and 1996 respectively. The horizontal crustal deformation and tectonic activity have been studied using GPS measurements. The GPS velocity fields are estimated and used to estimate the North China sub-plate and its intra-block rotation motions. Sub-plate and blocks rotations are discussed in detail by the study of GPS measurements, geology structural, and seismicity and paleomagnetic measurement. The current rotation pattern of Ordos block, Taihang block, Jiluxi block and Jiaoliao block all rotate in counterclockwise in ITRF96 frame. The relative motion of blocks for GPS data shows that activities of blocks agree with the activities of seismic and geological structure as a whole. Block Euler model using GPS data shows concord with active faults data, as well as Cenozoic paleomagnetic data. The Euler model of the sub-plate of North China also agrees with the NNR-NUVEL-1A model, which shows that North China sub-plate is of rigid characteristic. Chinese continent is bounded on the Eurasin plate, Indian plate and the Pacific plate, Its tectonic motion and deformation result in these interactive plates. Indian plate moves about 50mm every year to Eurasian plate in the southwest of Chinese continent, which results in an intensive push and press force northward in the western part of China. The Pacific plate subducted under the Eurasian plate, which caused a push and press force in SWW direction in the eastern part of China. From east to west in the Chinese continent, the principal compressive stress axis of tectonic stress field was deflected into NEE direction with nearly NS direction. Most of areas in the eastern part of China rotate clockwisly from the beginning of Oligocene. However, the Qinghaitibet plateau uplifted quickly and extended outside with the future colliding of the Eurasian plate and indian plate from Neogene, which resulted in an intensive push and press action in the NEE direction in the southern part of western boundary of the North China sub-plate. Thus there was a set of push and press forces acted on the western boundary of the Ordos block, these forces's magnitude decrease progressively from south to north, and their direction deflected into NEE direction with nearly EW direction from west to east. Considering the rigid characteristic of Ordos block and its adjacent blocks constrains, these forces resulted in counterclock rotating of Ordos block, Taihang block and Jiluxi block.