A Study On The Current Crustal Stress Field In Qiongzhou Strait

Qiongzhou Strait is one of China’s four Straits and is the sea hub of from the southeast coast to the Beibu Gulf, which located between the Leizhou Peninsula and Hainan Island. If Cross-sea Bridge or undersea tunne was achieved, the transport facilities would be greatly facilitated and followed by regional economic development promoting, and has great significance to the implementation of the national "21st Century Maritime Silk Road" development strategy.Qiongzhou Strait has a complicated geological conditions, high seismic intensity, environmental impact and lots of environmental influence sensitive points, the construction of the Cross Sea Engineering Project is very difficult. At present, research is focused in the waters geophysical surveys, in-situ ground stress research is in a very low degree and the basic problems of active faults has not been fully identified, the reliable information and data is not sufficient for engineering solutions. Thus, conductiong in-situ stress field research in Qiongzhou Straits and obtain more accurate data of ground stress field distribution, is of great significance, it can provide scientific basis for site selection and construction of the sea-crossing project.On the basis of detailed geological data collection, combined with regional tectonic background and geophysical field characteristics, analyzed the features of active fractures and characteristics of the crustal structure in the study area, and ascertained the material parameters of the earth’s crust layersd and major faults, then established three-dimensional model of the crustal structure in Qiongzhou Strait and adjacent areas. Using the finite element method, combined with regional ground stress field characteristics and stress measurement data of the study area to determine the boundary conditions and load models for the present ground stress field numerical simulation study, obtained the stress field spatial distribution of the study area, and analysis of the effects of active faults on the initial stress field, discussed the relationship between the seismic activities and the ground stress field of study area.The main research work and results are as follows:(1) A three-dimensional model of the crustal structure in the study area was established. The model includes major faults in the study area, the sedimentary cover (Cenozoic) and the crystalline basement, and the interface were simulated; (2) using ANS YS software to conduct the area situ stress field numerical simulation. Results show that the maximum principal stress value maximum principal stress in the raised area is large, its orientation is near the east-west, the direction of principal compressive stress axis is horizontal in the shallow parts of the crust and change into vertical with the increase of depth, and the crystalline basement significantly affected by gravity. Differential stress gradient decreased with increasing depth gradient. (3)The differential stress and the maximum principal stress show low values in the fracture, and the orientation of\principal stress occured a certain degree of deflection in nearby place of fractures. Strong earthquakes in the study area occurs mainly in the area of high stress concentration, deep horizontal stress axis orientation of the subject throughout the study area nearly SN direction, which is closed to the focal mechanism solution results.