Abstract: Trans-Bohai passage sea area lacks basic data on measured in-situ stress. Conducting in-situ measurements in this area is challenging and carries significant risks. To obtain firsthand data on the current in-situ stress field characteristics, a comprehensive in-situ stress measurement technology is employed. This technology primarily relies on hydraulic fracturing in-situ stress measurement, supplemented by methods such as hollow inclusion, inelastic strain recovery, differential strain, and acoustic anisotropy. Three-dimensional in-situ stress measurement and research are conducted in the sea area of the study region. A linear regression equation is established, and a regression fitting curve is obtained. The results reveal certain patterns: as the test depth increases in the Bohai strait, the maximum horizontal principal stress σ_H , minimum horizontal principal stress σ_h , and vertical principal stress σ_v  all increase linearly with the increase of test depth. In the southern part of the strait, the in-situ stress state follows the relationshipσ_H＞σ_h＞σ_v  , indicating a thrust stress state. The stress field direction is NE, with the maximum horizontal principal stress exceeding the vertical principal stress, suggesting dominance of tectonic forces in the region. In the northern part of the strait, the stress state is σ_H＞σ_v ＞σ_h , which is conducive to strike-slip fault activity. The stress field direction remains NE, and tectonic forces dominate in the region. Throughout the entire engineering region, there is minimal difference in each component value of the in-situ stress. These values are significantly lower than the lower limit of the active stress value of faults in the area, indicating that the study area is currently in a stable state. These findings align with the general principles of in-situ stress measurement. The testing process adheres to the requirements of in-situ stress testing, and the obtained data can be used to analyze the regional in-situ stress state.

Key words: trans-Bohai strait passage, 3D in-situ stress in the sea area of engineering region, comprehensive measurement technology