The Present-Day Crustal 3D Movement and Geodynamic Mechanisms in Hainan Island

The characteristics of the present-day crustal three dimensional (3D) movement with GNSS data during 1999-2018 and the precise leveling data during 1970s-2018 in Hainan Island and its adjacent area are analyzed. Based on the data and the horizontal movement field in the region of Southeast Asia, we discuss how the horizontal velocities in Hainan and the continental margin of the South China block (SCB) are affected by the Eurasian plate, the India-Australia plate and the Philippine Sea plate. The results show the movement of Hainan Island is the same as SCB. The horizontal velocities of the continental margin in South China are different in the east and the west along the boundary of the Northeastern Coast block and Yangtze Block. In Hainan Island, the 3D movement is different in two regions divided by Baisha fault. The movement of SCB is affected by Indo-European collision and extrusion. The movement of the continental margin is affected by both the Pacific Ocean plate, the Philippine Sea plate, the expansion of the South China Sea (SCS), the hot materials underplating and subsequent lithospheric extension. The effect on the regional movement by the Australia plate is smaller, but it can cause co-seismic step to SCB when there had a giant earthquake in Sumatra which is caused by the convergence of the Australia with the Sunda Plate in the NE direction.