Present-day Movement and Tectonic Strain Rate Field of Active Crustal Blocks in China Continent

Abstract

China continent, constructed by many blocks, is a dynamical system with complicated geological structure, topography and physiognomy. Since Cenozoic, it takes on different tectonic deformation in different blocks and the relative movement between neighboring blocks does always exist, which may be the key inducement of the strong seismic activity at the inner of China continent (Zhang Peizhen, 1999). In terms of tectonic movement feature, the continent can be divided into several different scalar crustal and lithosphere blocks, which include 6 active block regions that are Qinghai-Tibet, Xingjiang, Northeast, North China, South China and South China Sea block region, two active plate boundary tectonic zones and 29 active blocks that are Lhasa, Tian Shan etc. (Deng Qidong, Zhang Peizhen et al., 2003). In this paper, based on the bi-cubic Bessel spline function method, we inverted the present-day movement field of active blocks in China continent by combining with GPS measurements, seismic moment tensors of earthquakes and fault slip rates in China and its neighboring areas, considering about the geological and geophysical parameters at the same time. Furthermore, we inverted the strain rate field, strain energy density rate field, then we calculated the shearing strain rate field, area strain rate field and analyzed the relationship between the strong seismic activity and strain rate fields. The results reveal that in the middle and west of China continent, tectonic activity is stronger, particularly along the boundary zone of Himalayan block, in ChuanDian area of Qinghai-Tibet block and Tian Shan area of Xingjiang block, shearing strain rate is larger, the shearing strain rate fields are in correspondence with the tendency of present-day tectonic movement; from the distribution of principal axes of tectonic stress field, we can infer that present-day movement of active blocks in China continent is mainly caused by posthumous movement. The continent of China deformation has not only the strike-slip faulting and block’s transverse slip feature but also the crustal shortening and thickening feature, it doesn’t support the continental eastward escape theory of high-rate of slip.